Co-reporter:J. Philipp Wagner, Marcus A. Bartlett, Wesley D. Allen, and Michael A. Duncan
ACS Earth and Space Chemistry - New in 2017 August 17, 2017 Volume 1(Issue 6) pp:361-361
Publication Date(Web):July 13, 2017
DOI:10.1021/acsearthspacechem.7b00068
Formaldehyde (H2CO+) and methanol (H3COH+) radical cations, well-known in mass spectrometry, potentially form from radiative ionization or ion–molecule reactions in the interstellar medium. For both ions, other tautomeric forms exist that are accessible via [1,2]hydrogen shifts involving reaction barriers in excess of 25 kcal mol–1. Here, we compute the tunneling rates of the isomerization processes connecting the hydroxymethylene radical cation (HCOH+) to its more stable formaldehyde isomer (H2CO+) and the methanol radical cation (H3COH+) to its methylene oxonium isomer (H2COH2+) using the Wentzel–Kramers–Brillouin method at the CCSD(T)/cc-pVQZ//B3LYP/cc-pVTZ level of theory. While the hydroxymethylene radical cation features a half-life of over 3500 years and thus represents a potentially observable molecule, the methanol radical cation is predicted to decay with a half-life of about 4 days and is thus not likely to be present in appreciable quantities in space. We discuss the potential relevance of the hydroxymethylene and methylene oxonium cations for interstellar carbohydrate formation because both species represent potentially reactive, cationic, carbon-centered radicals.Keywords: formaldehyde; isomers; methanol; radical cations; tunneling;
Co-reporter:T.B. Ward, P.D. Carnegie, M.A. Duncan
Chemical Physics Letters 2016 Volume 654() pp:1-5
Publication Date(Web):16 June 2016
DOI:10.1016/j.cplett.2016.04.065
Highlights
- •
Ti(H2O)Arn+ ions are produced in a supersonic beam via a pulsed discharge.
- •
The infrared spectra of these ions are measured via IR laser photodissociation.
- •
Inserted HTiOH+ is more stable, but we detect only the Ti(H2O)+ ion–molecule complex.
- •
The ground state of Ti(H2O)+ is a quartet, while that of Ti(H2O)Ar+ is a doublet.
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Argon binding induces an electronic spin-state switch.
Co-reporter:D. Leicht, T.C. Cheng, M.A. Duncan
Chemical Physics Letters 2016 Volume 643() pp:89-92
Publication Date(Web):January 2016
DOI:10.1016/j.cplett.2015.11.018
•Glyoxal cations are produced in a supersonic beam via a pulsed discharge and mass selected.•The infrared spectrum of the glyoxal cation is measured via infrared laser photodissociation and argon tagging.•The infrared spectrum of glyoxal cation indicates the presence of only the trans conformer.•Glyoxal cation is only stable in the trans conformation according to DFT calculations.Glyoxal radical cations are produced in a pulsed discharge/supersonic molecular beam source. These ions are argon tagged and studied with mass-selected infrared laser photodissociation spectroscopy in the 1500–3500 cm−1 region. Five vibrational resonances are detected, three of which are assigned to two CH stretches and the asymmetric CO stretch fundamentals. Additional bands are assigned to vibrational combinations based on anharmonic frequency calculations. DFT calculations of the internal rotation coordinate, and the comparison of the predicted versus experimental IR spectra, show that the radical cation has only one stable structure, the trans conformer.
Co-reporter:Scott T. Akin, Vicente Zamudio-Bayer, Kaining Duanmu, Georg Leistner, Konstantin Hirsch, Christine Bülow, Arkadiusz Ławicki, Akira Terasaki, Bernd von Issendorff, Donald G. Truhlar, J. Tobias Lau, and Michael A. Duncan
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 22) pp:4568-4575
Publication Date(Web):October 25, 2016
DOI:10.1021/acs.jpclett.6b01839
Cobalt–benzene cluster ions of the form Co3(bz)n+ (n = 0–3) were produced in the gas phase, mass-selected, and cooled in a cryogenic ion trap held at 3–4 K. To explore ligand effects on cluster magnetic moments, these species were investigated with X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy. XMCD spectra yield both the spin and orbital angular momenta of these clusters. Co3+ has a spin magnetic moment of μS = 6 μB and an orbital magnetic moment of μL = 3 μB. Co3(bz)+ and Co3(bz)2+ complexes were found to have spin and orbital magnetic moments identical to the values for ligand-free Co3+. However, coordination of the third benzene to form Co3(bz)3+ completely quenches the high spin state of the system. Density functional theory calculations elucidate the spin states of the Co3(bz)n+ species as a function of the number of attached benzene ligands, explaining the transition from septet to singlet for n = 0 → 3.
Co-reporter:S. T. Akin, S. G. Ard, B. E. Dye, H. F. Schaefer, and M. A. Duncan
The Journal of Physical Chemistry A 2016 Volume 120(Issue 15) pp:2313-2319
Publication Date(Web):April 1, 2016
DOI:10.1021/acs.jpca.6b02052
Cerium oxide cluster cations, CexOy+, are produced via laser vaporization in a pulsed nozzle source and detected with time-of-flight mass spectrometry. The mass spectrum displays a strongly preferred oxide stoichiometry for each cluster with a specific number of metal atoms x, with x ≤ y. Specifically, the most prominent clusters correspond to the formula CeO(CeO2)n+. The cluster cations are mass selected and photodissociated with a Nd:YAG laser at either 532 or 355 nm. The prominent clusters dissociate to produce smaller species also having a similar CeO(CeO2)n+ formula, always with apparent leaving groups of (CeO2). The production of CeO(CeO2)n+ from the dissociation of many cluster sizes establishes the relative stability of these clusters. Furthermore, the consistent loss of neutral CeO2 shows that the smallest neutral clusters adopt the same oxidation state (IV) as the most common form of bulk cerium oxide. Clusters with higher oxygen content than the CeO(CeO2)n+ masses are present with much lower abundance. These species dissociate by the loss of O2, leaving surviving clusters with the CeO(CeO2)n+ formula. Density functional theory calculations on these clusters suggest structures composed of stable CeO(CeO2)n+ cores with excess oxygen bound to the surface as a superoxide unit (O2–).
Co-reporter:A. D. Brathwaite, H. L. Abbott-Lyon, and M. A. Duncan
The Journal of Physical Chemistry A 2016 Volume 120(Issue 39) pp:7659-7670
Publication Date(Web):September 14, 2016
DOI:10.1021/acs.jpca.6b07749
Carbonyl and nitrogen complexes with Rh+ are produced in a molecular beam using laser ablation and a pulsed-nozzle source. Mass-selected ions of the form Rh(CO)n+ and Rh(N2)n+ are investigated via infrared laser photodissociation spectroscopy. The fragmentation patterns and infrared spectra provide information on the coordination and geometries of these complexes. The shifts in vibrational frequencies relative to the uncoordinated ligands give insight into the nature of the bonding interactions involved. Experimental band positions and intensities are compared to those predicted by density functional theory (DFT). Rh+ coordinates only four nitrogen molecules, whereas it can accommodate five carbonyl ligands. The fifth CO ligand resides in an axial site with bonding intermediate between coordination and solvation. The carbonyl stretch in Rh(CO)4+ (2160 cm–1) is blue-shifted with respect to the molecular CO vibration (2143 cm–1). Conversely, the N–N stretch in Rh(N2)4+ (2297 cm–1) is red-shifted with respect to the free N2 vibration (2330 cm–1). The opposite directions of these frequency shifts is explained by a combination of σ donation and electrostatic ligand polarization.
Co-reporter:Jonathan D. Mosley, Justin W. Young, Michael A. Duncan
International Journal of Mass Spectrometry 2015 Volume 378() pp:322-327
Publication Date(Web):15 February 2015
DOI:10.1016/j.ijms.2014.10.003
•Infrared spectroscopy is reported for the C7H9+ cation produced in a discharge of norbornene and hydrogen.•Computational studies reveal 11 isomers of C7H9+ and their relative energies; p-protonated toluene is the global minimum structure.•In addition to p-protonated toluene, the infrared spectrum of the 1,3-dimethyl cyclopentadienyl cation is identified for the first time. This structure is significantly less stable than protonated toluene, but is obtained by kinetic trapping in the cold supersonic beam conditions.Protonated toluene (C7H9+) is a well-known stable carbocation, usually formed by σ-protonation of the parent molecule. Here, the corresponding C7H9+ ion is formed with a pulsed discharge in a supersonic expansion from a norbornene precursor. The different molecular framework of this precursor makes it possible to access different structural configurations. Infrared photodissociation spectroscopy is employed to characterize the C7H9+ ions produced. Protonated toluene is most abundant, however, new bands in the fingerprint and CH stretching regions indicate that another isomer is also present. Computational chemistry makes it possible to identify the 1,3-dimethylcyclopentadienyl cation, a less stable isomer not detected previously.
Co-reporter:Antonio D. Brathwaite, Timothy B. Ward, Richard S. Walters, and Michael A. Duncan
The Journal of Physical Chemistry A 2015 Volume 119(Issue 22) pp:5658-5667
Publication Date(Web):May 8, 2015
DOI:10.1021/acs.jpca.5b03360
Copper-acetylene cation complexes of the form Cu(C2H2)n+ (n = 1–8) are produced by laser ablation in a supersonic expansion of acetylene/argon. The ions are mass selected and studied via infrared laser photodissociation spectroscopy in the C–H stretching region (3000–3500 cm–1). The structure and bonding of these complexes are investigated through the number of infrared active bands, their relative intensities and their frequency positions. Density functional theory calculations are carried out in support of the experimental data. The combined data show that cation−π complexes are formed for the n = 1–3 species, resulting in red-shifted C–H stretches on the acetylene ligands. The coordination of the copper cation is completed with three acetylene ligands, forming a “propeller” structure with D3 symmetry. Surprisingly, complexes with even greater numbers of acetylenes than this (4–6) have distinctive infrared band patterns quite different from those of the smaller complexes. Experiment combined with theory establishes that there is a fascinating pattern of second-sphere solvation involving the binding of acetylenes in bifurcated CH−π binding sites at the apex of two core ligands. This binding motif leads to three equivalent sites for second-sphere ligands, which when filled form a highly symmetrical Cu+(C2H2)6 complex. Solvent binding in this complex induces a structural change to planarity in the core, producing an appealing “core–shell” structure with D3h symmetry.
Co-reporter:Jonathon A. Maner; Daniel T. Mauney
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 22) pp:4493-4498
Publication Date(Web):October 29, 2015
DOI:10.1021/acs.jpclett.5b02240
Ag+(benzene) complexes are generated in the gas phase by laser vaporization and mass selected in a time-of-flight spectrometer. UV laser excitation at either 355 or 266 nm results in dissociative charge transfer (DCT), leading to neutral silver atom and benzene cation products. Kinetic energy release in translationally hot benzene cations is detected using a new instrument designed for photofragment imaging of mass-selected ions. Velocity-map imaging and slice imaging techniques are employed. In addition to the expected translational energy release, DCT of Ag+(benzene) produces a distribution of internally hot benzene cations. Compared with experiments at 355 nm, 266 nm excitation produces only slightly higher translational excitation and a much greater fraction of internally hot benzene ions. The maximum kinetic energy release in the photodissociation sets an upper limit on the Ag+(benzene) dissociation energy of 32.8 (+1.4/–1.5) kcal/mol.
Co-reporter:Antonio D. Brathwaite, Jonathon A. Maner, and Michael A. Duncan
Inorganic Chemistry 2014 Volume 53(Issue 2) pp:1166-1169
Publication Date(Web):December 31, 2013
DOI:10.1021/ic402729g
Scandium and yttrium carbonyl cations produced in the gas phase via laser vaporization are mass selected and studied with infrared laser spectroscopy in the C–O stretching region. Mass spectra, ion fragmentation behavior, and infrared spectra, complemented by computational chemistry, establish the coordination numbers and structures of these complexes. Sc+ does not form the eight-coordinate 18-electron complex but instead produces a 16-electron seven-coordinate species. However, Y+ forms the anticipated eight-coordinate structure. Density functional theory computations provide structures and corresponding vibrational spectra for these complexes. Sc(CO)7+ has a C3v capped octahedral structure, while Y(CO)8+ forms a D4d square antiprism. The C–O stretches at 2086 and 2087 cm–1 for Sc(CO)7+ and Y(CO)8+, respectively, are among the most red-shifted frequencies measured for any transition metal carbonyl cation.
Co-reporter:Timothy M. Ayers, Scott T. Akin, Collin J. Dibble, and Michael A. Duncan
Journal of Chemical Education 2014 Volume 91(Issue 2) pp:291-296
Publication Date(Web):November 8, 2013
DOI:10.1021/ed4003942
New experiments for the undergraduate laboratory are described using laser desorption time-of-flight (TOF) mass spectrometry to produce and analyze a variety of inorganic nanoclusters. Laser vaporization of solid powder samples of sulfur, phosphorus, and bismuth all produce gas-phase cluster ions with unusual mass spectral patterns. This experiment provides an introduction to TOF mass spectrometry and ultrasmall nanoclusters, as well as hands-on experience in vacuum systems, lasers, oscilloscopes, and pulsed electronics. New concepts in chemical bonding for inorganic materials are explored.Keywords: Analytical Chemistry; Gases; Hands-On Learning/Manipulatives; Inorganic Chemistry; Laboratory Instruction; Lasers; Mass Spectrometry; Physical Chemistry; Upper-Division Undergraduate;
Co-reporter:Jonathan D. Mosley;Dr. Justin W. Young;Dr. Jay Agarwal; Henry F. Schaefer III; Paul v. R. Schleyer; Michael A. Duncan
Angewandte Chemie 2014 Volume 126( Issue 23) pp:5998-6001
Publication Date(Web):
DOI:10.1002/ange.201311326
Abstract
In an attempt to produce the 2-norbornyl cation (2NB+) in the gas phase, protonation of norbornene was accomplished in a pulsed discharge ion source coupled with a supersonic molecular beam. The C7H11+ cation was size-selected in a time-of-flight mass spectrometer and investigated with infrared laser photodissociation spectroscopy using the method of “tagging” with argon. The resulting vibrational spectrum, containing sharp bands in the CH stretching and fingerprint regions, was compared to that predicted by computational chemistry. However, the measured spectrum did not match that of 2NB+, prompting a detailed computational study of other possible isomers of C7H11+. This study finds five isomers more stable than 2NB+. The spectrum obtained corresponds to the 1,3-dimethylcyclopentenyl cation, the global minimum-energy structure for C7H11+, which is produced through an unanticipated ring-opening rearrangement path.
Co-reporter:Kimberly N. Reishus, Antonio D. Brathwaite, Jonathan D. Mosley, and Michael A. Duncan
The Journal of Physical Chemistry A 2014 Volume 118(Issue 35) pp:7516-7525
Publication Date(Web):March 12, 2014
DOI:10.1021/jp500778w
Singly charged aluminum–benzene cation complexes are produced by laser vaporization in a pulsed supersonic expansion. The Al+(benzene)n (n = 1–4) ions are mass selected and investigated with infrared laser photodissociation spectroscopy. Density functional theory (DFT) is employed to investigate the structures, energetics and vibrational spectra of these complexes. Spectra in the C–H stretching region exhibit sharp multiplet bands similar to the pattern known for the Fermi triad of the isolated benzene molecule. In the fingerprint region, strong bands are seen corresponding to the ν19 C–C ring motion and the ν11 out-of-plane hydrogen bend. The hydrogen bend is strongly blue-shifted compared to this vibration in benzene, whereas the ν19 carbon ring distortion is only slightly shifted to the red. Computed structures and energetics, together with experimental fragmentation and vibrational patterns, indicate a primary coordination of three benzene molecules around the central Al+ cation. The n = 4 complex contains one second-sphere solvent molecule.
Co-reporter:Jonathan D. Mosley;Dr. Justin W. Young;Dr. Jay Agarwal; Henry F. Schaefer III; Paul v. R. Schleyer; Michael A. Duncan
Angewandte Chemie International Edition 2014 Volume 53( Issue 23) pp:5888-5891
Publication Date(Web):
DOI:10.1002/anie.201311326
Abstract
In an attempt to produce the 2-norbornyl cation (2NB+) in the gas phase, protonation of norbornene was accomplished in a pulsed discharge ion source coupled with a supersonic molecular beam. The C7H11+ cation was size-selected in a time-of-flight mass spectrometer and investigated with infrared laser photodissociation spectroscopy using the method of “tagging” with argon. The resulting vibrational spectrum, containing sharp bands in the CH stretching and fingerprint regions, was compared to that predicted by computational chemistry. However, the measured spectrum did not match that of 2NB+, prompting a detailed computational study of other possible isomers of C7H11+. This study finds five isomers more stable than 2NB+. The spectrum obtained corresponds to the 1,3-dimethylcyclopentenyl cation, the global minimum-energy structure for C7H11+, which is produced through an unanticipated ring-opening rearrangement path.
Co-reporter:Sijie Luo, Collin J. Dibble, Michael A. Duncan, and Donald. G. Truhlar
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 15) pp:2528-2532
Publication Date(Web):July 9, 2014
DOI:10.1021/jz501167s
We studied the Co4O4 subnanocluster and its MeCN-coated species using density functional theory, and we found that the Co4O4 core presents distinctive structures in bare and ligand-coated species. We propose a possible ligand-mediated ring → cube transformation mechanism during the ligand-coating process of the Co4O4 core due to the stronger binding energies of the MeCN ligands to the 3D distorted cube structure than to the 2D ring and ladder structures; theory indicates that three ligands are sufficient to stabilize the cube structure. Both ring and cube structures are ferromagnetic. Our finding is potentially useful for understanding the catalysis mechanism of Co4O4 species, which have important applications in solar energy conversion and water splitting; these catalysis reactions usually involve frequent addition and subtraction of various ligands and thus possibly involve core rearrangement processes similar to our findings.Keywords: catalysis; cluster structure; magnetism; metal oxides; nanoparticles;
Co-reporter:T.C. Cheng, S.T. Akin, C.J. Dibble, S. Ard, M.A. Duncan
International Journal of Mass Spectrometry 2013 Volumes 354–355() pp:159-164
Publication Date(Web):15 November 2013
DOI:10.1016/j.ijms.2013.05.031
•Fullerene films are excited with infrared lasers and ions (positive and negative) are detected with time-of-flight mass spectrometry.•The mechanism of infrared desorption and ionization is investigated with different samples and IR wavelengths.•Tunable IR studies provide desorbed ion infrared spectra of C60, revealing new vibrational combination bands.Infrared laser excitation/desorption of thin film samples or powders containing fullerenes was observed to produce efficient ionization of both the fullerene and other molecules mixed into the sample. Both cations and anions were produced. The ions produced by this IR laser desorption ionization (IR-LDI) process were detected with a time-of-flight mass spectrometer. The mechanism of this IR-LDI process was investigated with mass spectra under different conditions, delayed pulse acceleration experiments, and IR wavelength dependence studies, employing either a fixed frequency CO2 laser (10.6 μm) or an IR optical parametric oscillator (2000–4500 cm−1; 5.0–2.2 μm). The mechanism of fullerene IR-LDI was found to involve both direct emission of electrons from alkali-fulleride impurities in the sample and multiple photon-induced thermionic (delayed) emission of electrons from hot fullerenes. In both cases, the electrons produced are accelerated by the source fields resulting in electron impact ionization of, or electron attachment to, neutral species in the outgoing plume of desorbed material. The IR-LDI process is enhanced on resonance with fullerene vibrations, suggesting the possibility of a new kind of laser-thin film spectroscopy.
Co-reporter:A. D. Brathwaite and M. A. Duncan
The Journal of Physical Chemistry A 2013 Volume 117(Issue 46) pp:11695-11703
Publication Date(Web):March 13, 2013
DOI:10.1021/jp400793h
Group IV metal carbonyl cations of the form M(CO)n+ (M = Ti, Zr, Hf; n = 6–8) are produced in a supersonic molecular beam via laser vaporization in a pulsed nozzle source. The ions are mass selected in a reflectron time-of-flight spectrometer and studied with infrared laser photodissociation spectroscopy in the carbonyl stretching region. The number of infrared active bands, their relative intensities, and their frequency positions provide insight into the structure and bonding of these complexes. Density functional theory calculations are employed to aid in the analysis of the experimental spectra. The n = 6 species is found to be the fully coordinated complex for each metal, and all analogues have a D3d structure. This symmetric structure and the resulting simple spectra facilitate the investigation of trends in the bonding and infrared band positions of these complexes. The carbonyl stretching frequencies of the M(CO)6+ species are all red-shifted with respect to the gas phase CO vibration at 2143 cm–1, occurring at 2110, 2094, and 2075 cm–1 for titanium, zirconium and hafnium. The magnitude of the red shift increases systematically going from titanium to hafnium.
Co-reporter:Allen M. Ricks, Antonio D. Brathwaite, and Michael A. Duncan
The Journal of Physical Chemistry A 2013 Volume 117(Issue 6) pp:1001-1010
Publication Date(Web):April 9, 2012
DOI:10.1021/jp301679m
The vibrational spectra of vanadium carbonyl cations of the form V(CO)n+, where n = 1–7, were obtained via mass-selected infrared laser photodissociation spectroscopy in the carbonyl stretching region. The cations and their argon and neon “tagged” analogues were produced in a molecular beam via laser vaporization in a pulsed nozzle source. The relative intensities and frequency positions of the infrared bands observed provide distinctive patterns from which information on the coordination and spin states of these complexes can be obtained. Density functional theory is carried out in support of the experimental spectra. Infrared spectra obtained by experiment and predicted by theory provide evidence for a reduction in spin state as the ligand coordination number increases. The octahedral V(CO)6+ complex is the fully coordinated experimental species. A single band at 2097 cm–1 was observed for this complex red-shifted from the free CO vibration at 2143 cm–1.
Co-reporter:J. W. Young, T. C. Cheng, B. Bandyopadhyay, and M. A. Duncan
The Journal of Physical Chemistry A 2013 Volume 117(Issue 32) pp:6984-6990
Publication Date(Web):January 29, 2013
DOI:10.1021/jp312630x
Cluster ions of H7+/D7+ and H9+/D9+ produced in a supersonic molecular beam with a pulsed discharge source are mass selected and studied with infrared laser photodissociation spectroscopy. Photodissociation occurs by the loss of H2 (D2) from each cluster, producing resonances in the 2000–4500 cm–1 region. Vibrational patterns indicate that these ions consist of an H3+ (D3+) core ion solvated by H2 (D2) molecules. There is no evidence for the shared proton structure seen previously for H5+. The H3+ ion core vibrational bands are weakened and broadened significantly, presumably by enhanced rates of intramolecular vibrational relaxation. Computational studies at the DFT/B3LYP or MP2 levels of theory (including scaling) are adequate to reproduce qualitative details of the vibrational spectra, but neither provides quantitative agreement with vibrational frequencies.
Co-reporter:Biswajit Bandyopadhyay, Kimberly N. Reishus, and Michael A. Duncan
The Journal of Physical Chemistry A 2013 Volume 117(Issue 33) pp:7794-7803
Publication Date(Web):July 22, 2013
DOI:10.1021/jp4046676
Singly charged zinc-water cations are produced in a pulsed supersonic expansion source using laser vaporization. Zn+(H2O)n (n = 1–4) complexes are mass selected and studied with infrared laser photodissociation spectroscopy, employing the method of argon tagging. Density functional theory (DFT) computations are used to obtain the structures and vibrational frequencies of these complexes and their isomers. Spectra in the O–H stretching region show sharp bands corresponding to the symmetric and asymmetric stretches, whose frequencies are lower than those in the isolated water molecule. Zn+(H2O)nAr complexes with n = 1–3 have O–H stretches only in the higher frequency region, indicating direct coordination to the metal. The Zn+(H2O)2–4Ar complexes have multiple bands here, indicating the presence of multiple low energy isomers differing in the attachment position of argon. The Zn+(H2O)4Ar cluster uniquely exhibits a broad band in the hydrogen bonded stretch region, indicating the presence of a second sphere water molecule. The coordination of the Zn+(H2O)n complexes is therefore completed with three water molecules.
Co-reporter:Allen M. Ricks, Antonio D. Brathwaite, and Michael A. Duncan
The Journal of Physical Chemistry A 2013 Volume 117(Issue 45) pp:11490-11498
Publication Date(Web):October 21, 2013
DOI:10.1021/jp4089035
Ion–molecule complexes of vanadium and CO2, i.e., V(CO2)n+, produced by laser vaporization are mass selected and studied with infrared laser photodissociation spectroscopy. Vibrational bands for the smaller clusters (n < 7) are consistent with CO2 ligands bound to the metal cation via electrostatic interactions and/or attaching as inert species in the second coordination sphere. All IR bands for these complexes are consistent with intact CO2 molecules weakly perturbed by cation binding. However, multiple new IR bands occur only in larger complexes (n ≥ 7), indicating the formation of an intracluster reaction product whose nominal mass is the same as that of V(CO2)n+ complexes. Computational studies and the comparison of predicted spectra for different possible reaction products allow identification of an oxalate-type C2O4 anion species in the cluster. The activation of CO2 producing this product occurs via a solvation-induced metal→ligand electron transfer reaction.
Co-reporter:Miguel Castro, Raul Flores, and Michael A. Duncan
The Journal of Physical Chemistry A 2013 Volume 117(Issue 47) pp:12546-12559
Publication Date(Web):November 12, 2013
DOI:10.1021/jp406581m
The ligand versus solvent behavior of Ni+(C6H6)3,4 complexes was studied using density functional theory all-electron calculations. Dispersion corrections were included with the BPW91-D2 method using the 6-311++G(2d,2p) basis set. The ground state (GS) for Ni+(C6H6)3 has three benzene rings 3d−π bonded to the metal. A two-layer isomer with two moieties coordinated η3–η2 with Ni+, and the other one adsorbed by van der Waals interactions to the Ni+(C6H6)2 subcluster, i.e., a 2 + 1 structure, is within about 8.4 kJ/mol of the GS. Structures with 3 + 1 and 2 + 2 ligand coordination were found for Ni+(C6H6)4. The binding energies (D0) of 28.9 and 26.0 kJ/mol for the external moieties of Ni+(C6H6)3,4 are much smaller than that for Ni+(C6H6)2, 193.0 kJ/mol, obtained also with BPW91-D2. This last D0 overestimates somehow the experimental value, of 146.7 ± 11.6 kJ/mol, for Ni+(C6H6)2. The abrupt fall for D0(Ni+(C6H6)3,4) shows that such molecules are bound externally as solvent species. These results agree with the D0(Ni+(C6H6)3) < 37.1 kJ/mol limit found experimentally for this kind of two-layer clusters. The ionization energies also decrease for m = 2, 3, and 4 (580.8, 573.1, and 558.6 kJ/mol). For Ni+(C6H6)3,4, each solvent moiety bridges the benzenes of Ni+(C6H6)2; their position and that of one internal ring mimics the tilted T-shape geometry of the benzene dimer (Bz2). The distances from the center of the external to the center of the internal rings for m = 3 (4.686 Å) and m = 4 (4.523 Å) are shorter than that for Bz2 (4.850 Å). This and charge transfer effects promote the (Cδ−–Hδ+)int dipole−πext interactions in Ni+(C6H6)3,4; π–π interactions also occur. The predicted IR spectra, having multiplet structure in the C–H region, provide insight into the experimental spectra of these ions.
Co-reporter:A. D. Brathwaite, A. M. Ricks, and M. A. Duncan
The Journal of Physical Chemistry A 2013 Volume 117(Issue 50) pp:13435-13442
Publication Date(Web):August 8, 2013
DOI:10.1021/jp4068697
Mass selected vanadium oxide–carbonyl cations of the form VOm(CO)n+ (m = 0–3 and n = 3–6) are studied via infrared laser photodissociation spectroscopy in the 600–2300 cm–1 region. Insight into the structure and bonding of these complexes is obtained from the number of infrared active bands, their relative intensities and their frequency positions. Density functional theory calculations are carried out in support of the experimental data. The effect of oxidation on the carbonyl stretching frequencies of VO(CO)n+, VO2(CO)n+, and VO3(CO)n+ complexes is investigated. All of these oxide–carbonyl species have C–O stretch vibrations blue-shifted from those of the pure vanadium ion carbonyls. The V–O stretches of these complexes are also investigated, revealing the effects of CO coordination on these vibrations. The oxide–carbonyls all have a hexacoordinate core analogous to that of V(CO)6+. The fully coordinated vanadium monoxide–carbonyl species is VO(CO)5+, and those of the dioxide and trioxide are VO2(CO)4+ and VO3(CO)3+, respectively.
Co-reporter:Timothy C. Cheng ; Biswajit Bandyopadhyay ; Jonathan D. Mosley
Journal of the American Chemical Society 2012 Volume 134(Issue 31) pp:13046-13055
Publication Date(Web):July 18, 2012
DOI:10.1021/ja3038245
The structure of ions in water at a hydrophobic interface influences important processes throughout chemistry and biology. However, experiments to measure these structures are limited by the distribution of configurations present and the inability to selectively probe the interfacial region. Here, protonated nanoclusters containing benzene and water are produced in the gas phase, size-selected, and investigated with infrared laser spectroscopy. Proton stretch, free OH, and hydrogen-bonding vibrations uniquely define protonation sites and hydrogen-bonding networks. The structures consist of protonated water clusters binding to the hydrophobic interface of neutral benzene via one or more π-hydrogen bonds. Comparison to the spectra of isolated hydronium, zundel, or eigen ions reveals the inductive effects and local ordering induced by the interface. The structures and interactions revealed here represent key features expected for aqueous hydrophobic interfaces.
Co-reporter:J. D. Mosley, A. M. Ricks, P. v. R. Schleyer, J. I. Wu, and M. A. Duncan
The Journal of Physical Chemistry A 2012 Volume 116(Issue 39) pp:9689-9695
Publication Date(Web):September 11, 2012
DOI:10.1021/jp307631n
Protonated pyrrole cations are produced in a pulsed discharge/supersonic expansion source, mass-selected in a time-of-flight spectrometer, and studied with infrared photodissociation spectroscopy. Vibrational spectra in both the fingerprint and C–H/N–H stretching regions are obtained using the method of tagging with argon. Sharp vibrational structure is compared to IR spectra predicted by theory for the possible α-, β-, and N-protonated structures. The spectral differences among these isomers are much larger than the frequency shifts due to argon attachment at alternative sites. Though α-protonation predominates thermodynamically, the kinetically favored β-protonated species is also observed for the first time (in 3–4 times lower abundance under the conditions employed here). Theoretical investigations attribute the greater stability of α-protonated pyrrole to topological charge stabilization, rather than merely to the greater number of resonance contributors. The far-IR pattern of protonated pyrrole does not match the interstellar UIR bands.
Co-reporter:Rodrigo Garza-Galindo, Miguel Castro, and Michael A. Duncan
The Journal of Physical Chemistry A 2012 Volume 116(Issue 8) pp:1906-1913
Publication Date(Web):February 7, 2012
DOI:10.1021/jp2117533
The interactions of the iron monocation with water molecules and argon atoms in the gas phase were studied computationally to elucidate recent infrared vibrational spectroscopy on this system. These calculations employ first-principles all-electron methods performed with B3LYP/DZVP density functional theory. The ground state of Fe+(H2O) is found to be a quartet (M = 2S + 1 = 4, S is the total spin). Different binding sites for the addition of one or two argon atoms produce several low-lying states of different geometry and multiplicity in a relatively small energy range for Fe+(H2O)–Ar2 and Fe+(H2O)2–Ar. In both species, quartet states are lowest in energy, and sextets and doublets lie at higher energies from the respective ground states. These results are consistent with the conclusion that the experimentally determined infrared photodissociation spectra (IRPD) of Fe+(H2O)–Ar2 and Fe+(H2O)2–Ar are complicated because of the presence of multiple isomeric structures. The estimated IR bands for the symmetric and asymmetric O–H stretches from different isomers provide new insight into the observed IRPD spectra.
Co-reporter:Timothy C. Cheng, Ling Jiang, Knut R. Asmis, Yimin Wang, Joel M. Bowman, Allen M. Ricks, and Michael A. Duncan
The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 21) pp:3160-3166
Publication Date(Web):October 15, 2012
DOI:10.1021/jz301276f
H5+ is the smallest proton-bound dimer. As such, its potential energy surface and spectroscopy are highly complex, with extreme anharmonicity and vibrational state mixing; this system provides an important benchmark for modern theoretical methods. Unfortunately, previous measurements covered only the higher-frequency region of the infrared spectrum. Here, spectra for H5+ and D5+ are extended to the mid- and far-IR, where the fundamental of the proton stretch and its combinations with other low-frequency vibrations are expected. Ions in a supersonic molecular beam are mass-selected and studied with multiple-photon dissociation spectroscopy using the FELIX free electron laser. A transition at 379 cm–1 is assigned tentatively to the fundamental of the proton stretch of H5+, and bands throughout the 300–2200 cm–1 region are assigned to combinations of this mode with bending and torsional vibrations. Coupled vibrational calculations, using ab initio potential and dipole moment surfaces, account for the highly anharmonic nature of these complexes.Keywords: infrared spectroscopy; interstellar ions; ion spectroscopy; mass spectrometry; photodissociation; shared proton;
Co-reporter:B. Bandyopadhyay, M.A. Duncan
Chemical Physics Letters 2012 530() pp: 10-15
Publication Date(Web):
DOI:10.1016/j.cplett.2012.01.048
Co-reporter:C. J. Dibble, S. T. Akin, S. Ard, C. P. Fowler, and M. A. Duncan
The Journal of Physical Chemistry A 2012 Volume 116(Issue 22) pp:5398-5404
Publication Date(Web):May 18, 2012
DOI:10.1021/jp302560p
Cobalt and nickel oxide cluster cations, CoxOy+ and NixOy+, are produced by laser vaporization of metal rods in a pulsed nozzle cluster source and detected using time-of-flight mass spectrometry. The mass spectra show prominent stoichiometries of x = y for CoxOy+ along with x = y and x = y – 1 for NixOy+. The cluster cations are mass selected and multiphoton photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. Although various channels are observed, photofragmentation exhibits two main forms of dissociation processes in each system. CoxOy+ dissociates preferentially through the loss of O2 and the formation of cobalt oxide clusters with a 1:1 stoichiometry. The Co4O4+ cluster seems to be particularly stable. NixOy+ fragments reveal a similar loss of O2, although they are found to favor metal-rich fragments with stoichiometries of NixOx–1. The Ni2O+ fragment is produced from many parent ions. The patterns in fragmentation here are not nearly as strong as those seen for early or mid-period transition-metal oxides studied previously.
Co-reporter:B. Bandyopadhyay, T. C. Cheng, S. E. Wheeler, and M. A. Duncan
The Journal of Physical Chemistry A 2012 Volume 116(Issue 26) pp:7065-7073
Publication Date(Web):June 7, 2012
DOI:10.1021/jp304091h
Protonated benzene cluster ions, H(C6H6)2+ and H(C6H6)3+, are produced in a pulsed electrical discharge source coupled to a supersonic expansion. Mass-selected complexes are investigated with infrared photodissociation spectroscopy in the 1000–3200 cm–1 region using the method of argon tagging. The IR spectra of H(C6H6)2+–Ar and H(C6H6)3+–Ar contain broad bands in the high frequency region resulting from CH−π hydrogen bonds. Sharp peaks are observed in the fingerprint region arising from the ring modes of both the C6H7+ and C6H6 moieties. M06-2X calculations have been performed to investigate the structures and vibrational spectra of energetically low-lying configurations of these complexes. H(C6H6)2+ is predicted to have three nearly isoenergetic conformers: the parallel displaced (PD), T-shaped (TS), and canted (C) structures [Jaeger, H. M.; Schaefer, H. F.; Hohenstein, E. G.; Sherrill, C. D. Comput. Theor. Chem. 2011, 973, 47–52]. A comparison of the experimental dimer spectrum with those predicted for the three isomers suggests an average structure between the TS and PD conformers, which is consistent with the low energy barrier predicted to separate these two structures. No evidence is found for the C dimer even though it lies only 1.2 kcal/mol above the PD dimer. Although the trimer is also computed to have many low lying isomers, the IR spectrum limits the possible species present.
Co-reporter:Antonio D. Brathwaite and Michael A. Duncan
The Journal of Physical Chemistry A 2012 Volume 116(Issue 5) pp:1375-1382
Publication Date(Web):January 12, 2012
DOI:10.1021/jp211578t
Si(CO)n+ and Si(CO)n+Ar complexes are produced via laser vaporization with a pulsed nozzle source and cooled in a supersonic beam. The ions are mass selected in a reflectron time-of-flight mass spectrometer and studied with infrared laser photodissociation spectroscopy near the free molecular CO vibration (2143 cm–1). Si(CO)n+ complexes larger than n = 2 fragment by the loss of CO, whereas Si(CO)n+Ar complexes fragment by the loss of argon. All clusters have resonances near the free molecular CO stretch that provide distinctive patterns from which information on their structure and bonding can be obtained. The number of infrared-active bands, their frequency positions, and relative intensities indicate that larger species consist of an asymmetrically coordinated Si(CO)2+ core with additional CO ligands attached via van der Waals interactions. Density functional theory computations are carried out in support of the experimental spectra.
Co-reporter:J. D. Mosley, T. C. Cheng, A. B. McCoy, and M. A. Duncan
The Journal of Physical Chemistry A 2012 Volume 116(Issue 37) pp:9287-9294
Publication Date(Web):September 4, 2012
DOI:10.1021/jp3072298
Pulsed discharges containing methanol or ethanol produce ions having the nominal formula [C,H3,O]+, i.e. m/z = 31. Similar ions resulting from electron impact ionization in mass spectrometers are long recognized to have either the CH2OH+ protonated formaldehyde or CH3O+ methoxy cation structures. The H2OCH+ oxonio-methylene structure has also been suggested by computational chemistry. To investigate these structures, ions are expanded in a supersonic beam, mass-selected in a time-of-flight spectrometer, and studied with infrared laser photodissociation spectroscopy. Sharp bands in the O–H and C–H stretching and fingerprint regions are compared to computational predictions for the three isomeric structures and their vibrational spectra. Protonated formaldehyde is the most abundant isomer, but methoxy is also formed with significant abundance. The branching ratio of these two ion species varies with precursors and formation conditions.
Co-reporter:A.M. Knight, B. Bandyopadhyay, C.L. Anfuso, K.S. Molek, M.A. Duncan
International Journal of Mass Spectrometry 2011 Volume 304(Issue 1) pp:29-35
Publication Date(Web):15 June 2011
DOI:10.1016/j.ijms.2011.03.005
Indium oxide cations of the form InnOm+ are produced by laser vaporization in a pulsed nozzle source and detected with time of flight mass spectrometry. The In2O+ and In3O+ ions have high relative intensities in the mass spectra of clusters sampled directly from the source. Cluster cations are mass-selected and photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. The elimination of indium cation is the dominant loss channel for all cluster cations. However, certain other clusters, i.e., In2O+, In2O2, In3O+ and In3O2+ are produced as fragments from several cluster sizes and are thus identified as particularly stable. Density functional theory calculations are employed for selected species to determine their structures and relative stabilities. The Wade–Mingos electron counting rules are found to be inappropriate for these systems because their bonding is primarily ionic.Graphical abstractHighlights► Indium oxide cluster cations are produced in a laser vaporization source and analyzed with time-of-flight mass spectrometry. ► Cluster ions are mass-selected and photodissociated at 355 nm. Prominent photofragments are In+, In2O+, In2O2, In3O+ and In3O2+. ► Density functional theory finds linear structures for many small clusters and confirms the relative stabilities of prominent photofragments.
Co-reporter:A.M. Ricks, Z.E. Reed, M.A. Duncan
Journal of Molecular Spectroscopy 2011 Volume 266(Issue 2) pp:63-74
Publication Date(Web):April 2011
DOI:10.1016/j.jms.2011.03.006
Metal carbonyl cations of the form M(CO)n+ are produced in a molecular beam by laser vaporization in a pulsed nozzle source. These ions, and their corresponding rare gas atom “tagged” analogs, M(CO)n(RG)m+, are studied with mass-selected infrared photodissociation spectroscopy in the carbonyl stretching region and with density functional theory computations. The number of infrared-active bands, their frequency positions, and their relative intensities provide distinctive patterns allowing determination of the geometries and electronic structures of these complexes. Cobalt penta carbonyl and manganese hexacarbonyl cations are compared to isoelectronic iron pentacarbonyl and chromium hexacarbonyl neutrals. Gold and copper provide examples of “non-classical” carbonyls. Seven-coordinate carbonyls are explored for the vanadium group metal cations (V+, Nb+ and Ta+), while uranium cations provide an example of an eight-coordinate carbonyl.Graphical abstractBack-bonding is the most important factor determining the C–O stretching frequencies of metal carbonyls, and cations are less efficient at this than neutrals.Highlights► Metal carbonyl cations are produced in a molecular beam by laser vaporization. ► Ions are mass-selected and studied with IR photodissociation spectroscopy. ► C–O stretching frequencies are measured for M(CO)n+ cations for n = 1–9. ► C–O frequencies for cations are compared to those for neutrals. ► Stable coordination numbers vary from two to eight for different metals.
Co-reporter:S. Ard ; C. J. Dibble ; S. T. Akin ;M. A. Duncan
The Journal of Physical Chemistry C 2011 Volume 115(Issue 14) pp:6438-6447
Publication Date(Web):March 4, 2011
DOI:10.1021/jp200691k
Subnanometer vanadium oxide clusters in the 10−30 atom size range are produced in the gas phase with laser vaporization, coated with gas-phase ligands, and then captured in solution using a laser vaporization flow reactor. Acetonitrile (MeCN) and tetrahydrofuran (THF) ligands form complexes efficiently with the oxide clusters, rendering them soluble in solutions of these same ligands and other solvents. The structures and compositions of clusters captured in solution are investigated with laser desorption time-of-flight (LD-TOF) mass spectrometry, UV−visible and IR spectroscopy, and density functional theory computations. MeCN forms oxide clusters having the exact stoichiometries found previously to be stable in the gas phase (V3O6, V4O9, and V5O12), in a simple ligand-addition process. THF produces similar oxide cores, but with terminal oxygens displaced. Infrared spectra are consistent with the presence of terminal oxygens for the MeCN complexes and their absence for the THF species. In either case, DFT computations show that the vanadium oxide cores are minimally perturbed by ligand addition. Solutions of both samples exhibit visible photoluminescence with only minor dependence on the ligand, indicating that the core oxide is the source of the emission.
Co-reporter:Allen M. Ricks, Laura Gagliardi, and Michael A. Duncan
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 14) pp:1662-1666
Publication Date(Web):June 22, 2011
DOI:10.1021/jz2006868
The UO4+ and UO6+ cations are produced in a supersonic molecular beam by laser vaporization and studied with infrared laser photodissociation spectroscopy using rare gas atom predissociation. The argon complexes UO4+Ar2 and UO6+Ar2 are mass-selected in a reflectron time-of-flight spectrometer and excited with an IR-OPO laser system in the range of the O–U–O and O–O stretching vibrations. These same systems are studied with computational quantum chemistry. UO4+ is found to have a central UO2 core, with an additional η2 coordinated oxygen molecule. Charge transfer/oxidation gives the system the character of a UO22+, O2– ion pair. UO6+ has this same core structure, with an additional weakly bound oxygen molecule in an η1 coordination configuration. The O–U–O stretch is sensitive to the local environment and approximates the vibration of the isolated uranyl cation in these systems.Keywords: computational chemistry; infrared spectroscopy; oxides; photodissociation;
Co-reporter:P. D. Carnegie, B. Bandyopadhyay, and M. A. Duncan
The Journal of Physical Chemistry A 2011 Volume 115(Issue 26) pp:7602-7609
Publication Date(Web):May 28, 2011
DOI:10.1021/jp203501n
Singly and doubly charged manganese–water cations, and their mixed complexes with attached argon atoms, are produced by laser vaporization in a pulsed nozzle source. Complexes of the form Mn+(H2O)Arn (n = 1–4) and Mn2+(H2O)Ar4 are studied via mass-selected infrared photodissociation spectroscopy, detected in the mass channels corresponding to the elimination of argon. Sharp resonances are detected for all complexes in the region of the symmetric and asymmetric stretch vibrations of water. With the guidance of density functional theory computations, specific vibrational band resonances are assigned to complexes having different argon attachment configurations. In the small singly charged complexes, argon adds first to the metal ion site and later in larger clusters to the hydrogens of water. The doubly charged complex has argon only on the metal ion. Vibrations in all of these complexes are shifted to lower frequencies than those of the free water molecule. These shifts are greater when argon is attached to hydrogen and also greater for the dication compared to the singly charged species. Cation binding also causes the IR intensities for water vibrations to be much greater than those of the free water molecule, and the relative intensities are greater for the symmetric stretch than the asymmetric stretch. This latter effect is also enhanced for the dication complex.
Co-reporter:A. D. Brathwaite, Z. D. Reed, and M. A. Duncan
The Journal of Physical Chemistry A 2011 Volume 115(Issue 38) pp:10461-10469
Publication Date(Web):August 24, 2011
DOI:10.1021/jp206102z
Copper carbonyl cations of the form Cu(CO)n+ (n = 1–8) are produced in a molecular beam via laser vaporization in a pulsed nozzle source. Mass-selected infrared photodissociation spectroscopy in the carbonyl stretching region is used to study these ions and their argon “tagged” analogues. The geometries and electronic states of these complexes are determined by the number of infrared-active bands, their frequency positions, and their relative intensities compared to the predictions of theory. Cu(CO)4+ has a completed coordination sphere, consistent with its expected 18-electron stability. It also has a tetrahedral structure similar to that of its neutral isoelectronic analog Ni(CO)4. The carbonyl stretch in Cu(CO)4+ (2198 cm–1) is blue-shifted with respect to the free CO vibration (2143 cm–1), providing evidence that this is a “non-classical” metal carbonyl.
Co-reporter:Allen M. Ricks ; Laura Gagliardi
Journal of the American Chemical Society 2010 Volume 132(Issue 45) pp:15905-15907
Publication Date(Web):October 22, 2010
DOI:10.1021/ja1077365
Uranium and uranium dioxide carbonyl cations produced by laser vaporization are studied with mass-selected ion infrared spectroscopy in the C−O stretching region. Dissociation patterns, spectra, and quantum chemical calculations establish that the fully coordinated ions are U(CO)8+ and UO2(CO)5+, with D4d square antiprism and D5h pentagonal bipyramid structures. Back-bonding in U(CO)8+ causes a red-shifted CO stretch, but back-donation is inefficient for UO2(CO)5+, producing a blue-shifted CO stretch characteristic of nonclassical carbonyls.
Co-reporter:B. Bandyopadhyay, T.C. Cheng, M.A. Duncan
International Journal of Mass Spectrometry 2010 Volume 297(1–3) pp:124-130
Publication Date(Web):1 November 2010
DOI:10.1016/j.ijms.2010.07.010
Cluster ions containing hydronium and multiple nitrogen molecules, e.g., H3O+(N2)n (n = 1–4) are produced in a supersonic molecular beam using a pulsed discharge source. Ions are mass analyzed and size-selected using a reflectron time-of-flight mass spectrometer. Selected ions are investigated with infrared laser photodissociation spectroscopy in the 2000–4000 cm−1 region. Photodissociation occurs by the loss of a single nitrogen molecule from each cluster. The infrared spectra contain free-OH vibrations, hydrogen bonding O–H vibrations, combination bands between the latter vibrations and the low-frequency intermolecular stretches, and an N–N stretch in the n = 4 clusters. The n = 1 cluster has partially resolved rotational structure, confirming that its structure is that of end-on addition of N2 to one of the hydrogens of hydronium. The hydrogen bonding bands have broad linewidths and are significantly red-shifted from the free-OH vibrations. The red-shift decreases when more nitrogens are added, as the shared-proton interaction is distributed over the three hydrogen binding sites. Proton sharing in this system is highly biased toward the water moiety, but the nitrogen interaction is significant enough to induce significant vibrational shifts compared to other weakly bound complexes with hydronium (e.g., argon).Hydronium nitrogen cluster ions are studied in the free-OH and hydrogen bonding regions with infrared photodissociation spectroscopy.
Co-reporter:Zach D. Reed
Journal of The American Society for Mass Spectrometry 2010 Volume 21( Issue 5) pp:739-749
Publication Date(Web):2010 May
DOI:10.1016/j.jasms.2010.01.022
Manganese carbonyl cations of the form Mn(CO)n+ (n = 1−9) are produced in a molecular beam by laser vaporization in a pulsed nozzle source. Mass selected infrared photodissociation spectroscopy in the carbonyl stretching region is used to study these complexes and their “argon-tagged” analogues. The geometries and electronic states of these complexes are determined by comparing their infrared spectra to theoretical predictions. Mn(CO)6+ has a completed coordination sphere, consistent with its predicted 18-electron stability. It has an octahedral structure in its singlet ground state, similar to its isoelectronic analogue Cr(CO)6. Charge-induced reduction in π back-bonding leads to a decreased red-shift in Mn(CO)6+ (υCO = 2106 cm−1) compared with Cr(CO)6 (υCO = 2003 cm−1). The spin multiplicity of Mn+(CO)n complexes gradually decreases with progressive ligand addition. MnCO+ is observed as both a quintet and a septet, Mn(CO)2+ is observed only as a quintet, while Mn(CO)3,4+ are both observed as triplets. Mn(CO)5+ and Mn(CO)6+ are both singlets, as are all larger complexes.
Co-reporter:Timothy C. Cheng, Biswajit Bandyopadyay, Yimin Wang, Stuart Carter, Bastiaan J. Braams, Joel M. Bowman and Michael A. Duncan
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 4) pp:758-762
Publication Date(Web):February 1, 2010
DOI:10.1021/jz100048v
We report experimental and calculated infrared spectra of the highly fluxional cations H5+ and D5+. These cations have been postulated to exist in the interstellar medium and to play a central role in the deuterium fractionation. The experiments produce these ions in a pulsed discharge supersonic nozzle ion source and utilize mass-selected photodissociation spectroscopy in the 2000−4500 cm−1 region. Vibrational bands apparently broadened by rapid predissociation are detected throughout this region for both isotopologues. The calculated spectra make use of an ab initio potential energy surface and a new dipole moment surface and are based on results from fixed-node quantum diffusion Monte Carlo and variational vibrational calculations. The successful assignment of the experimental spectra requires a proper treatment of the delocalized anharmonic shared-proton mode and indicates a major breakdown of the harmonic approximation. Several calculated intense spectral features associated with this mode in the far-infrared region could guide future observational searches of these cations.Keywords (keywords): D5+; diffusion Monte Carlo; H5+; infrared spectroscopy; vibrational dynamics;
Co-reporter:G. E. Douberly, R. S. Walters, J. Cui, K. D. Jordan and M. A. Duncan
The Journal of Physical Chemistry A 2010 Volume 114(Issue 13) pp:4570-4579
Publication Date(Web):March 16, 2010
DOI:10.1021/jp100778s
Infrared photodissociation spectroscopy is reported for mass-selected H+(H2O)n complexes and their deuterated analogues with and without argon “tagging.” H+(H2O)nArm and D+(D2O)nArm complexes are studied in the O−H (O−D) stretching region for clusters in the small size range (n = 2−5). Upon infrared excitation, these clusters fragment by the loss of either argon atoms or one or more intact water molecules. Their excitation spectra show distinct bands in the region of the symmetric and asymmetric stretches of water and in the hydrogen bonding region. Experimental studies are complemented by computational work that explores the isomeric structures, their energetics and vibrational spectra. The addition of an argon atom is essential to obtain photodissociation for the n = 2−3 complexes, and specific inclusion of the argon in calculations is necessary to reproduce the measured spectra. For n = 3−5, spectra are obtained both with and without argon. The added argon atom allows selection of a subset of colder clusters and it increases the photodissociation yield. Although most of these clusters have more than one possible isomeric structure, the spectra measured correspond to a single isomer that is computed to be the most stable. Deuteration in these small cluster sizes leads to expected lowering of frequencies, but the spectra indicate the presence of the same single most-stable isomer for each cluster size.
Co-reporter:Allen M. Ricks ; Zach D. Reed
Journal of the American Chemical Society 2009 Volume 131(Issue 26) pp:9176-9177
Publication Date(Web):June 12, 2009
DOI:10.1021/ja903983u
Gas-phase metal carbonyl cations of the vanadium-group metals (V+, Nb+, Ta+) were produced in a molecular beam by laser vaporization and then mass-analyzed and size-selected in a time-of-flight spectrometer and studied with IR laser photodissociation spectroscopy in the carbonyl-stretching region. The abundances in the mass spectra, the fragmentation patterns, and the IR spectra provided a combined approach that revealed the coordination numbers in these systems. Although seven-coordinate structures would have 18 electrons in each case, V(CO)6+ was found to be formed rather than V(CO)7+. Nb+ formed both six- and seven-coordinate species, while Ta+ formed only the Ta(CO)7+ complex. Density functional theory computations were used to predict the IR spectra for these systems, which are dramatically different for the six- and seven-coordinate structures and in excellent agreement with the measurements. V(CO)6+ and Nb(CO)6+ have structures slightly distorted from octahedral, while Nb(CO)7+ and Ta(CO)7+ have C3v capped octahedral structures.
Co-reporter:Allen M. Ricks, Gary E. Douberly, Paul v.R. Schleyer, Michael A. Duncan
Chemical Physics Letters 2009 Volume 480(1–3) pp:17-20
Publication Date(Web):28 September 2009
DOI:10.1016/j.cplett.2009.08.063
Co-reporter:A.M. Ricks, G.E. Douberly, M.A. Duncan
International Journal of Mass Spectrometry 2009 Volume 283(1–3) pp:69-76
Publication Date(Web):1 June 2009
DOI:10.1016/j.ijms.2009.01.009
O4+ and larger (O2)n+ cluster ions are produced in a pulsed discharge source and studied with time-of-flight mass spectrometry and infrared laser photodissociation spectroscopy. The infrared laser photon energies used allow bracketing of the cluster dissociation energies. Sharp resonant structure is detected for each of these ions in the region of the O–O stretching vibrations and also at higher frequencies corresponding to combination bands. Although previous matrix isolation spectroscopy on O4+ found evidence for both trans-bent and rectangular isomers of this ion, the gas phase IR spectrum only contains bands assigned to the rectangular isomer. O6+ has a distinctive IR spectrum unlike that for O4+, indicating that it is not simply a solvated O4+ species, while O8+ has the signature of a solvated O6+ ion.
Co-reporter:P. D. Carnegie, A. B. McCoy and M. A. Duncan
The Journal of Physical Chemistry A 2009 Volume 113(Issue 17) pp:4849-4854
Publication Date(Web):April 6, 2009
DOI:10.1021/jp901231q
Copper−water ion−molecule complexes with attached argon atoms, Cu+(H2O)Ar2, are produced in a supersonic molecular beam by pulsed laser vaporization. These systems are mass-selected in a reflectron time-of-flight spectrometer and studied with infrared photodissociation spectroscopy. The vibrational spectra for these complexes are characteristic of many cation−water systems, exhibiting symmetric and asymmetric O−H stretch fundamentals, and weaker features at higher frequency that have been tentatively assigned to combination bands. Using isotopically substituted spectra and model potential calculations, we are able to assign the combination bands to a water torsional vibration (frustrated rotation) in combination with the asymmetric stretch fundamental. This combination band assignment is likely to apply to IR spectra of many cation−water complexes.
Co-reporter:Gary E. Douberly, Allen M. Ricks and Michael A. Duncan
The Journal of Physical Chemistry A 2009 Volume 113(Issue 30) pp:8449-8453
Publication Date(Web):July 6, 2009
DOI:10.1021/jp9052709
We report infrared predissociation spectra of size-selected D+(D2O)n clusters in the size range n = 18−24 for comparison to previous studies of the corresponding H+(H2O)n species (Shin, J.-W.; Hammer, N. I.; Diken, E. G.; Johnson, M. A.; Walters, R. S.; Jaeger, T. D.; Duncan, M. A.; Christie, R. A.; Jordon, K. D. Science 2004, 304, 1137). For n = 18−20, two “free” OD stretch bands are observed and assigned to D2O molecules in acceptor−acceptor−donor (AAD) and acceptor−donor (AD) hydrogen bonding arrangements. Only the AAD band is observed for the n = 21 perdeuterated species. This behavior is identical to that observed previously for the corresponding H+(H2O)n clusters. Similar to the all-H protonated species, the AD “free” OD stretch band is also absent for the perdeuterated n = 22 cluster but returns for clusters larger than n = 22. Like the H+(H2O)n systems, the perdeuterated clusters have no spectral band in the lower frequency range where the signature of the hydronium cation is predicted. These observations shed new light on the intriguing spectroscopy and dynamics of large protonated water clusters.
Co-reporter:A. M. Ricks, J. M. Bakker, G. E. Douberly and M. A. Duncan
The Journal of Physical Chemistry A 2009 Volume 113(Issue 16) pp:4701-4708
Publication Date(Web):March 16, 2009
DOI:10.1021/jp900239u
Cobalt carbonyl cations of the form Co(CO)n+ (n = 1−9) are produced in a molecular beam by laser vaporization in a pulsed nozzle source. These ions, and their corresponding “argon-tagged” analogues, Co(CO)n(Ar)m+, are studied with mass-selected infrared photodissociation spectroscopy in the carbonyl stretching region. The number of infrared-active bands, their frequency positions, and their relative intensities provide distinctive patterns allowing determination of the geometries and electronic structures of these complexes. Co(CO)5+ has a completed coordination sphere, consistent with its expected 18-electron stability, and it has the same structure (D3h trigonal bipyramid) as its neutral isoelectronic analog Fe(CO)5. The carbonyl stretches in Co(CO)5+ are less red-shifted than those in Fe(CO)5 because of charge-induced reduction in the π back-bonding. Co(CO)1−4+ complexes have triplet ground states, but the spin changes to a singlet for the Co(CO)5+ complex.
Co-reporter:Gary E. Douberly, Allen M. Ricks, Brian W. Ticknor and Michael A. Duncan
Physical Chemistry Chemical Physics 2008 vol. 10(Issue 1) pp:77-79
Publication Date(Web):22 Nov 2007
DOI:10.1039/B716165D
The infrared spectra of protonated acetone and the proton bound acetone dimer are obtained revealing vibrational resonances associated with the shared proton motions, which are in agreement with the predictions from ab initio, MP2, harmonic frequency calculations.
Co-reporter:G. E. Douberly, A. M. Ricks, P. v. R. Schleyer and M. A. Duncan
The Journal of Physical Chemistry A 2008 Volume 112(Issue 22) pp:4869-4874
Publication Date(Web):May 7, 2008
DOI:10.1021/jp802020n
Gas phase C6H7+ and C7H9+ ions are studied with infrared photodissociation spectroscopy (IRPD) and the method of rare gas tagging. The ions are produced in a pulsed electric discharge supersonic expansion source from benzene or toluene precursors. We observe exclusively the formation of either the C2v benzenium ion (protonated benzene) or the para isomer of the toluenium ion (protonated toluene). The infrared spectral signatures associated with each ion are established between 750 and 3400 cm−1. Comparing the gas phase spectrum of the benzenium ion to the spectrum obtained in a superacid matrix [Perkampus, H. H.; Baumgarten, E. Angew. Chem. Int. Ed. 1964, 3, 776], we find that the C2v structure of the gas phase species is minimally affected by the matrix environment. An intense band near 1610 cm−1 is observed for both ions and is indicative of the allylic π-electron density associated with the six membered ring in these systems. This spectral signature, also observed for alkyl substituted benzenium ions and protonated naphthalene, compares favorably with the interstellar, unidentified infrared emission band near 6.2 µm (1613 cm−1).
Co-reporter:Z. D. Reed and M. A. Duncan
The Journal of Physical Chemistry A 2008 Volume 112(Issue 24) pp:5354-5362
Publication Date(Web):May 22, 2008
DOI:10.1021/jp800588r
Transition metal oxide cations of the form MnOm+ (M = Y, La) are produced by laser vaporization in a pulsed nozzle source and detected with time-of-flight mass spectrometry. Cluster oxides for each value of n form only a limited number of stoichiometries; MO(M2O3)x+ species are particularly intense. Cluster cations are mass selected and photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. Multiphoton excitation is required to dissociate these clusters because of their strong bonding. Yttrium and lanthanum oxides exhibit different dissociation channels, but some common trends can be identified. Larger clusters for both metals undergo fission to make certain stable cation clusters, especially MO(M2O3)x+ species. Specific cations are identified to be especially stable because of their repeated production in the decomposition of larger clusters. These include M3O4+, M5O7+, M7O10+, and M9O13+, along with Y6O8+. Density functional theory calculations were performed to investigate the relative stabilities and structures of these systems.
Co-reporter:P. D. Carnegie, B. Bandyopadhyay and M. A. Duncan
The Journal of Physical Chemistry A 2008 Volume 112(Issue 28) pp:6237-6243
Publication Date(Web):June 19, 2008
DOI:10.1021/jp803086v
Singly and doubly charged chromium−water ion−molecule complexes are produced by laser vaporization in a pulsed-nozzle cluster source. These species are detected and mass-selected in a specially designed time-of-flight mass spectrometer. Vibrational spectroscopy is measured for these complexes in the O−H stretching region using infrared photodissociation spectroscopy and the method of rare gas atom predissociation. Infrared excitation is not able to break the ion−water bonds in these systems, but it leads to elimination of argon, providing an efficient mechanism for detecting the spectrum. The O−H stretches for both singly and doubly charged complexes are shifted to frequencies lower than those for the free water molecule, and the intensity of the symmetric stretch band is strongly enhanced relative to the asymmetric stretch. Partially resolved rotational structure for both complexes shows that the H−O−H bond angle is greater than it is in the free water molecule. These polarization-induced effects are enhanced in the doubly charged ion relative to its singly charged analog.
Co-reporter:K. S. Molek, C. Anfuso-Cleary and M. A. Duncan
The Journal of Physical Chemistry A 2008 Volume 112(Issue 39) pp:9238-9247
Publication Date(Web):May 13, 2008
DOI:10.1021/jp8009436
Iron oxide cluster cations, FenOm+, are produced by laser vaporization in a pulsed nozzle cluster source and detected with time-of-flight mass spectrometry. The mass spectrum exhibits a limited number of stoichiometries for each value of n, where m ≥ n. The cluster cations are mass selected and photodissociated using the second (532 nm) or third (355 nm) harmonic of a Nd:YAG laser. At either wavelength, multiple photon absorption is required to dissociate these clusters, which is consistent with their expected strong bonding. Cluster dissociation occurs via elimination of molecular oxygen, or by fission processes producing stable cation species. For clusters with n < 6, oxygen elimination proceeds until a terminal stoichiometry of n = m is reached. Clusters with this 1:1 stoichiometry do not eliminate oxygen, but rather undergo fission, producing smaller (FeO)n+ species. The decomposition of larger clusters produces a variety of product cations, but those with the 1:1 stoichiometry are always the most prominent and these same species are produced repeatedly from different parent ions. These combined results establish that species of the form (FeO)n+ have the greatest stability throughout these small iron oxide clusters.
Co-reporter:B. W. Ticknor, B. Bandyopadhyay and M. A. Duncan
The Journal of Physical Chemistry A 2008 Volume 112(Issue 48) pp:12355-12366
Publication Date(Web):November 7, 2008
DOI:10.1021/jp807867r
Noble metal carbide cluster cations (MCn+, M = Cu, Au) are produced by laser vaporization in a pulsed molecular beam and detected with time-of-flight mass spectrometry. Copper favors the formation of carbides with an odd number of carbon atoms, while gold shows marked drops in ion intensity after clusters with 3, 6, 9, and 12 carbons. These clusters are mass selected and photodissociated at 355 nm. Copper carbides with an odd number of carbons fragment by eliminating the metal from the cluster; for the small species it is eliminated as Cu+ and for the larger species it is lost as neutral Cu. Copper carbides with an even number of carbons also lose the metal, but in addition to this they eliminate neutral C3. This even−odd alternation, with the even clusters having mixed fragments, holds true for clusters as large as CuC30+. No loss of C2 is observed for even the largest clusters studied, indicating that fullerene formation does not occur. The gold carbide photodissociation data closely parallel that of copper, with even clusters losing primarily C3 and odd ones losing gold. Comparisons to known carbon cluster ionization potentials give some insight into the structures of carbon photofragments. DFT calculations performed on CuC3−11+ allow comparisons of the energetics of isomers likely present in our experiment, and metal−carbon dissociation energies help explain the even−odd alternation in the fragmentation channels. The simplest picture of these metal-doped carbides consistent with all the data is that the small species have linear chain structures with the metal attached at the end, whereas the larger species have cyclic structures with the metal attached externally to a single carbon.
Co-reporter:Jeffrey M. Headrick;Eric G. Diken;Richard S. Walters;Nathan I. Hammer;Richard A. Christie;Jun Cui;Evgeniy M. Myshakin;Mark A. Johnson;Kenneth D. Jordan
Science 2005 Vol 308(5729) pp:1765-1769
Publication Date(Web):17 Jun 2005
DOI:10.1126/science.1113094
Abstract
The ease with which the pH of water is measured obscures the fact that there is presently no clear molecular description for the hydrated proton. The mid-infrared spectrum of bulk aqueous acid, for example, is too diffuse to establish the roles of the putative Eigen (H3O+) and Zundel (H5O2+) ion cores. To expose the local environment of the excess charge, we report how the vibrational spectrum of protonated water clusters evolves in the size range from 2 to 11 water molecules. Signature bands indicating embedded Eigen or Zundel limiting forms are observed in all of the spectra with the exception of the three- and five-membered clusters. These unique species display bands appearing at intermediate energies, reflecting asymmetric solvation of the core ion. Taken together, the data reveal the pronounced spectral impact of subtle changes in the hydration environment.
Co-reporter:J.-W. Shin;N. I. Hammer;E. G. Diken;M. A. Johnson;R. S. Walters;T. D. Jaeger;M. A. Duncan;R. A. Christie;K. D. Jordan
Science 2004 Vol 304(5674) pp:1137-1140
Publication Date(Web):21 May 2004
DOI:10.1126/science.1096466
Abstract
We report the OH stretching vibrational spectra of size-selected H+(H2O)n clusters through the region of the pronounced “magic number” at n = 21 in the cluster distribution. Sharp features are observed in the spectra and assigned to excitation of the dangling OH groups throughout the size range 6 ≤ n ≤ 27. A multiplet of such bands appears at small cluster sizes. This pattern simplifies to a doublet at n = 11, with the doublet persisting up to n = 20, but then collapsing to a single line in the n = 21 and n = 22 clusters and reemerging at n = 23. This spectral simplification provides direct evidence that, for the magic number cluster, all the dangling OH groups arise from water molecules in similar binding sites.
Co-reporter:T.D Jaeger, A Fielicke, G von Helden, G Meijer, M.A Duncan
Chemical Physics Letters 2004 Volume 392(4–6) pp:409-414
Publication Date(Web):11 July 2004
DOI:10.1016/j.cplett.2004.05.057
Abstract
Vanadium cluster cations with one, two or three adsorbed water molecules are investigated with infrared photodissociation spectroscopy in the region of the bending mode of water. In all of these complexes, the bending mode of adsorbed water is measured near the corresponding frequency of the isolated molecule. Dissociation processes are efficient, indicating that these resonances are characteristic of a substantial fraction of all complexes present. This indicates that water is adsorbed without significant dissociation on these clusters. Clusters with two or three water molecules have similar resonances near the bending mode of free water, indicating independent absorption without hydrogen bonding.
Co-reporter:D van Heijnsbergen, T.D Jaeger, G von Helden, G Meijer, M.A Duncan
Chemical Physics Letters 2002 Volume 364(3–4) pp:345-351
Publication Date(Web):4 October 2002
DOI:10.1016/S0009-2614(02)01341-6
The Al–benzene complex is produced by laser vaporization in a pulsed nozzle source. It is ionized with an ArF excimer laser (193 nm), and the Al+(benzene) ions are stored in a quadrupole ion trap. Infrared excitation with a tunable free electron laser induces multiphoton photodissociation, and fragment ions are analyzed by a time-of-flight mass spectrometer. The infrared spectrum of Al+(benzene) is measured with resonance-enhanced multiphoton photodissociation (IR-REMPD) spectroscopy. Bands in the region correspond to benzene vibrations shifted by the metal bonding. The spectrum indicates that Al+ binds in the symmetric η6π configuration on the benzene molecule.
Co-reporter:Zach D. Reed, Michael A. Duncan
Journal of the American Society for Mass Spectrometry (May 2010) Volume 21(Issue 5) pp:739-749
Publication Date(Web):1 May 2010
DOI:10.1016/j.jasms.2010.01.022
Manganese carbonyl cations of the form Mn(CO)n+ (n = 1–9) are produced in a molecular beam by laser vaporization in a pulsed nozzle source. Mass selected infrared photodissociation spectroscopy in the carbonyl stretching region is used to study these complexes and their “argon-tagged” analogues. The geometries and electronic states of these complexes are determined by comparing their infrared spectra to theoretical predictions. Mn(CO)6+ has a completed coordination sphere, consistent with its predicted 18-electron stability. It has an octahedral structure in its singlet ground state, similar to its isoelectronic analogue Cr(CO)6. Charge-induced reduction in π back-bonding leads to a decreased red-shift in Mn(CO)6+ (υCO = 2106 cm−1) compared with Cr(CO)6 (υCO = 2003 cm−1). The spin multiplicity of Mn+(CO)n complexes gradually decreases with progressive ligand addition. MnCO+ is observed as both a quintet and a septet, Mn(CO)2+ is observed only as a quintet, while Mn(CO)3,4+ are both observed as triplets. Mn(CO)5+ and Mn(CO)6+ are both singlets, as are all larger complexes.Infrared spectroscopy of mass-selected ions provides new insights into metal carbonyl structure and bonding.Download high-res image (92KB)Download full-size image
Co-reporter:J.A. Maner, D.T. Mauney, M.A. Duncan
Chemical Physics Letters (March 2017) Volume 671() pp:
Publication Date(Web):March 2017
DOI:10.1016/j.cplett.2017.01.042
•Ar2+ ions are produced via laser spark in a supersonic expansion.•The photodissociation of Ar2+ is studied at 355 nm using velocity map imaging.•355-nm excitation leads to the 2Σg+ ← 2Σu+ transition with β = 1.71–1.95.•The dissociation energy of Ar2+ is determined to be D0″ = 1.32 +0.03/−0.02 eV.The argon dimer cation is produced in a plasma generated by a laser spark in a supersonic expansion. The cold ions are mass selected and investigated by photodissociation at 355 nm, with velocity map imaging of the Ar+ photofragment. Using the radius of the image, we determine the kinetic energy release and derive the ground state dissociation energy of Ar2+ as D0″ = 1.32 +0.03/−0.02 eV. Additionally, the angular distribution is described with β = 1.71–1.95, consistent with excitation of the parallel-type 2Σg+ ← 2Σu+ transition.
Co-reporter:Gary E. Douberly, Allen M. Ricks, Brian W. Ticknor and Michael A. Duncan
Physical Chemistry Chemical Physics 2008 - vol. 10(Issue 1) pp:NaN79-79
Publication Date(Web):2007/11/22
DOI:10.1039/B716165D
The infrared spectra of protonated acetone and the proton bound acetone dimer are obtained revealing vibrational resonances associated with the shared proton motions, which are in agreement with the predictions from ab initio, MP2, harmonic frequency calculations.
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![Bicyclo[2.2.1]hept-2-ylium](/data/chemimg/1161800/24321-81-1.png)
![Bicyclo[2.2.1]hept-2-ylium](/data/chemimg/1161800/24321-81-1_b.png)
