A series of yttrium oxide–carbonyls are prepared via a laser vaporization supersonic cluster source in the gas phase and identified by mass-selected infrared photodissociation (IRPD) spectroscopy in the C–O stretching region and by comparing the observed IR spectra with those from quantum chemical calculations. For YO(CO)4+, all four CO ligands prefer to occupy the equatorial site of the YO+ unit, leading to a quadrangular pyramid with C4v symmetry. Two energetically nearly degenerate isomers are responsible for YO(CO)5+, in which the fifth CO ligand is either inserted into the equatorial plane of YO(CO)4+ or coordinated opposite the oxygen on the C4 axis. YO(CO)6+ has a pentagonal bipyramidal structure with C5v symmetry, which includes five equatorial CO ligands and one axial CO ligand. The present IRPD spectroscopic and theoretical study of YO(CO)n+ extends the first shell coordination number of CO ligands in metal monoxide carbonyls to six. The transition from equatorial to axial CO chemisorption in these yttrium oxide–carbonyls is fortunately observed at n = 5, providing new insight into ligand interactions and coordination for the transition metal oxides.

M(N2)n+ (M = Y, La, Ce; n = 7–8) complexes have been studied by infrared photodissociation (IRPD) spectroscopy and density functional theory (DFT) calculations. The experimental results indicate that the N–N stretching vibrational frequencies are red-shifted from the gas-phase N2 value. The π back-donation is found to be a main contributor in these systems. IRPD spectra and DFT calculations reveal the coexistence of two isomers in the seven-coordinate M(N2)7+ and eight-coordinate M(N2)8+ complexes, respectively. The present studies on these metal–nitrogen complexes shed light on the interactions and coordinations toward N2 with transition and lanthanide metals.

Joint research of photoelectron velocity map imaging spectroscopy and density functional theory has been performed to probe the geometrical structures and electronic properties for heterodinuclear iron–lead carbonyl cluster PbFe(CO)4–, which serves as a monomer of the metal–metal bonded oligomer. The photoelectron detachment of PbFe(CO)4– is recorded at two different photon energies with rich spectral features. The ground-state transition obtained at 532 nm reveals a broad vibrationally resolved spectral band, which corresponds to the lead–iron stretching, while the 355 nm spectrum displays many more transitions on the higher-energy side, which correspond to the electronic excited states of PbFe(CO)4. Theoretical calculations at the B3LYP level are performed to explore the ground states of both the anionic and neutral PbFe(CO)4 and to support spectral identification of the fine resolved photoelectron spectra. Moreover, the unique chemical bonding between lead and iron in PbFe(CO)4 is discussed with the aid of natural bond orbital analyses.

•A novel in-situ pyrolysis time-of-flight mass spectrometry is employed.•Double ionization sources (VUVPI/EI) are used to ionize volatile products.•The release of small species is related to the pyrolysis of chemical groups.•The different structures of two lignites cause different pyrolytic species.Pyrolytic species of two kinds of lignites (samples A and B) are investigated in-situ with pyrolysis-vacuum ultraviolet photoionization/electron impact mass spectrometry (PVUVPI/EIMS). Mass spectra of pyrolytic fragments are measured during temperature-programmed pyrolysis process of two lignite samples and the intensity profiles of the pyrolytic species are estimated in different temperatures. Experimental results show that H2, H2O, CO, and CO2 are dominant inorganic gaseous products and their characteristic temperatures are in accord with the temperatures of related chemical bonds cleavage. Mononuclear aromatics are dominant organic pyrolysis products, and many olefin species are also identified. The differences between samples A and B on macromolecular structures make the distribution of pyrolytic products different. In addition, the peak of H2S and CH3SH are both clearly observed in mass spectra of sample B, which could come from thioether bonds decomposition. This work also illustrates that the PVUVPI/EIMS performs very well in in-situ analysis pyrolytic products.

•We obtained IR photodissociation spectra of MO(CO)5+ (M = Sc, Y, La and Ce) in the gas phase.•We studied the structures of MO(CO)5+ (M = Sc, Y, La and Ce) using DFT calculations.•The dominant structures of MO(CO)5+ (M = Sc, Y, La and Ce) have C5v geometry.The MO(CO)5+ (M = Sc, Y, La and Ce) complexes are generated and analyzed using an infrared photodissociation spectrometer. Their CO stretching frequencies are determined to be 2210 cm−1, 2206 cm−1, 2198 cm−1 and 2196 cm−1 for M = Sc, Y, La and Ce, respectively. The simulated spectra from DFT calculations are compared with the experimental results, indicating MO(CO)5+ (M = Sc, Y, La and Ce) are or very close to pentagonal pyramidal structures with C5V symmetry. The comparisons of these complexes with other metal carbonyls help to elucidate the characteristics of CO coordination in various metal species.

The homoleptic heterodinuclear copper–nickel carbonyl anions CuNi(CO)n– (n = 2–4) were generated in a pulsed-laser vaporization source and investigated using photoelectron velocity-map imaging spectroscopy. The electron affinities of CuNi(CO)2 (2.15 ± 0.03 eV), CuNi(CO)3 (2.30 ± 0.03 eV), and CuNi(CO)4 (1.90 ± 0.04 eV) were deduced from the photoelectron spectra. Theoretical calculations at the B3LYP level were carried out to elucidate the structures and the electronic properties of CuNi(CO)n0/1– (n = 1–4) and to support the experimental observations. Comprehensive comparisons between experiments and calculations suggest that there is a turnover point of the absorption site during the progressive carbonylation process. The carbonyl groups are determined to be preferentially bonded to the nickel atom. When the nickel center satisfies the 18-electron configuration, the copper atom starts to adsorb additional CO molecules. These results will shed light on the bonding mechanisms of the heterometallic carbonyl clusters.

We have combined photoelectron velocity-map imaging (VMI) spectroscopy and theoretical calculations to elucidate the geometry and energy properties of Aux−(Solv)n clusters with x = 1, 2; n = 1, 2; and Solv = H2O and CH3OH. Besides the blue-shifted vertical electron detachment energies (VDEs) of the complexes Au1,2−(Solv)n with the increase of the solvation number (n), we independently probed two distinct Au−(CH3OH)2 isomers, which combined with MP2/aug-cc-pVTZ(pp) calculations represent a competition between O⋯H–O hydrogen bonds (HBs) and Au⋯H–O nonconventional hydrogen bonds (NHBs). Complementary calculations provide the total binding energies of the low-energy isomers. Moreover, the relationship between the total binding energies and total VDEshift is discussed. We found that the Au1,2− anions exhibit halide-analogous behavior in microsolvation. These findings also demonstrate that photoelectron velocity map imaging spectroscopy with the aid of the ab initio calculations is an effective tool for investigating weak-interaction complexes.

Pyrolysis of three α,ω-diarylalkane compounds (biphenyl, diphenylmethane, and bibenzyl) was performed below 30 Pa between 573 and 1473 K. Vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry was used to detect the reactants, radicals, and products. The relative concentration profiles of the pyrolysis species were estimated by a semi-quantitative analysis method. Experimental results indicated that the length of the C–C bridge bond plays an influential role in cracking of corresponding bonds in the α,ω-diarylalkane pyrolysis process. The C–H bond scission is dominant in pyrolysis of diphenylmethane at low temperatures, while the C–C bond scission competes with it when the temperature increases. The symmetrical homolysis of bibenzyl is a dominant reaction at low temperatures and will compete with the unsymmertrical cleavage reaction with increase of the temperature. In addition, the formation mechanism of fluorene, which plays a significant role in polycyclic aromatic hydrocarbon generation, during diphenylmethane pyrolysis was discussed by combining the experimental observation with the theoretical calculation. The theoretical calculation supported these experimental results at the mPW2PLYP level.

An experimental study of three coal-based model compound (anisole, phenyl ethyl ether, and p-methyl anisole) pyrolysis was carried out at low pressure (below 50 Pa) within the temperature range from 573 to 1323 K. The pyrolysis process was investigated by detecting the reactants, radicals, and products using vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry. The similarities and differences of three model compounds in the pyrolysis process were discussed. The results suggested that the radical reactions were dominant in the pyrolysis process at higher temperatures, whereas the intermolecular reactions were significant at lower temperatures. β–H was a key factor for the non-radical reactions. The PhO–C homolytic bond scission was the first step for the radical reaction. Substituents on the benzene ring play an important role in the pyrolysis process of phenyl ethers, which can directly form conjugated stable structure compounds. These observations were supported by our theoretical calculation at the mPW2PLYP level.

We report a combined photoelectron velocity map imaging spectroscopy and density functional theory investigation on the Au3H– anion. Transition between the anionic electronic ground state and the neutral electronic ground state is revealed. Vibrationally resolved spectra were recorded at two different photon energies, providing a wealth of spectroscopic information for the electronic ground state of the Au3H. Franck–Condon simulations of the ground-state transition are carried out to assist in the assignment of the vibrationally resolved spectra. The electron affinity and vertical detachment energy of Au3H are measured to be 2.548 ± 0.001 and 2.570 ± 0.001 eV, respectively. Three stretching vibrational modes are determined to be activated upon photodetachment, with the frequencies of 2100 ± 100, 177 ± 10, and 96 ± 10 cm–1.

We first demonstrate the photoelectron spectroscopic evidence of the transition of two competitive solvation patterns in the Au–(CH3OH)n (n = 1–5) clusters. Quantum chemical calculations have been carried out to characterize the geometric structures, energy properties and hydrogen-bonded patterns, and to aid the spectral assignment. It has been found that the nonconventional hydrogen bonds dominate the small clusters (n = 1 and 2), whereas the conventional hydrogen bonds play more and more important role from n = 2 to n = 5. This finding provides concrete hydrogen bond network evolution of Au– surrounded by methanol molecules.

The octacoordinate metal carbonyls La(CO)8+ and Ce(CO)8+ were observed in laser vaporization of La and Ce in pure CO gas. The peak intensities in the mass spectra, the infrared photodissociation spectra, and the theoretical calculations indicate that all CO ligands in these two complexes are bonded with the central metal atoms. The CO stretching frequencies in La(CO)8+ and Ce(CO)8+ are determined to be 2110 and 2108 cm–1, respectively. Theoretical studies indicate that the most stable structures for La(CO)8+ and Ce(CO)8+ are an Oh geometry at its triplet state and a slightly distorted Oh geometry at its quartet state, respectively. These two complexes represent new octacoordinate metal carbonyls after previously determined U(CO)8+ and Y(CO)8+.

Vibrationally resolved photoelectron spectra have been obtained for Cu2H– and AgCuH– using photoelectron imaging at 355 nm. Two transition bands X and A are observed for each spectrum. The X bands in both spectra show the vibration progressions of the Cu–H stretching mode and the broad peaks of these progressions indicate significant structural changes from Cu2H– and AgCuH– to their neutral ground states. The A bands in the spectra of Cu2H– and CuAgH– show stretching progressions of Cu–Cu and Ag–Cu, respectively. The contours of these two progressions are pretty narrow, indicating relatively small structural changes from Cu2H– and AgCuH– to their neutral excited states. Calculations based on density functional theory indicate that the ground states of Cu2H– and AgCuH– and the first excited states of their neutrals are linear, whereas their neutral ground states are bent. The photoelectron detachment energies and vibrational frequencies from these calculations are in good agreement with the experimental observations. Especially, the theoretical predication of linear structures for the anions and the neutral excited states are supported by the spectral features of A bands, in which the bending modes are inactive. Comparisons among the vertical detachment energies of Cu2H–, AgCuH–, and their analogs help to elucidate electronic characteristics of coinage metal elements and hydrogen in small clusters.

Bimetallic clusters of MPb5– (M = Cu, Ag, and Au) have been studied using density functional theory and photoelectron imaging spectroscopy. These anionic clusters and their neutrals were determined to be a Pb5 trigonal bipyramid with the coinage metal atom on its triangular facet. This structure of each MPb5– or MPb5 was found to be more than 0.5 eV lower than other structural candidates and that of each MPb5– has a HOMO–LUMO gap of larger than 1.2 eV. The chemical bonding between M and Pb5 in MPb5– was dominantly attributed to the interaction between the outer s orbital of M and the lowest unoccupied molecular orbital (LUMO) of Pb5. The inner d orbitals of M and the occupied orbitals of Pb5 unit only make a little contribution. The different bonding behaviors of Cu, Ag, and Au, which are noticeable in many other species, have little effect on the Pb5 counterpart in MPb5–, indicating Pb5 unit acts partially like a large artificial atom. Additionally, photoelectron spectra of MPb5– (M = Cu, Ag, and Au) provide good experimental data to evaluate different theoretical approaches dealing with relativistic effects in clusters containing heavy atoms.

Structures and electronic properties of the mixed metal hydride anions AuAgH−, Au2AgH−, AuAg2H− and their neutrals are studied using anionic photoelectron imaging and theoretical calculations. The three isomers of AuAgH− are determined to be linear and those of AuAgH are determined to have Cs symmetry. The structures of Au2AgH−, AuAg2H− and their corresponding neutrals are determined to be planar with Cs or C2v symmetries. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these anions are reported. Similar to the homonuclear Aum− and Agn− clusters, the metal hydride anions with an even number of valence electrons have higher VDEs than those with an odd number. Variation of the VDEs of these metal hydride anions with interchange of Au, Ag and H (for example AumAgn− → Aum−1Agn+ 1−, or Aum−1AgnH−) will be shown to be characterized by the electronegativities of Au, Ag and H. The results presented in this study provide important insights into the similar and different characteristics of these three elements in small clusters.

Bimetallic clusters of AgCu–, AgCu2–, and Ag2Cu– are investigated by using photoelectron imaging and theoretical calculations. Their photoelectron spectra have been obtained at the wavelength of 355 nm and that of AgCu– is also acquired at 1064 nm. The ground state vertical detachment energies of these three clusters are measured to be 0.96 (1), 2.39 (5), and 2.41 (5) eV. The ground state adiabatic detachment energy of AgCu– is measured to be 0.93 (1) eV. Other spectroscopic constants of AgCu– including its frequency, bond length, and dissociation energy (relative to the products Ag– and Cu) are determined to be 191(15) cm–1, 2.487(10) Å, and 1.39 eV according to its spectrum at 1064 nm. Only upper limits of the ground state adiabatic detachment energies of AgCu2– and Ag2Cu– are estimated by using their spectra at 355 nm. The structures and properties of AgCu–, AgCu2–, Ag2Cu–, and their neutral counterparts are also computed by using a strategy where the structural optimizations are performed with the PW91PW91 method and the energy calculations are performed with the CCSD (T) method. The calculations are in better agreement with the experiments than most of the previous theoretical work.

Photodetachment of AgX– (X = Cl, Br, I) and AuCl– is studied by a photoelectron velocity map imaging technique and theoretical calculations. Photoelectron spectra (PES) and photoelectron angular distributions (PADs) were obtained. The vibrationally resolved spectra provided approximately equal electron affinities (EAs) for AgX: 1.593(22) eV for AgCl, 1.623(21) eV for AgBr, and 1.603(22) eV for AgI, respectively. Franck–Condon simulations of these spectra gave the equilibrium bond lengths and vibrational frequencies of the title anions. Relativistic density functional theory (DFT) calculations using BLYP, PW91, PBE, and BP86 functionals have been performed to predict the EAs of the AgX (X = Cl, Br, I) molecules. The computed EAs at the BP86 level of theory are in good agreement with the experimental values. Energy partitioning analyses (EPA) at the BP86(ZORA)/QZ4P level of theory of both anions and their neutrals were reported.

Activation of the C–H bond of pyridine by [Mm]− (M = Cu, Ag, Au, m = 1–3) is investigated by experiment and theory. Complexes of coinage metal clusters and the pyridyl group, [Mm–C5H4N]−, are produced from reactions between metal clusters formed by laser ablation of coinage metal samples and pyridine molecules seeded in argon carrier gas. We examine the structure and formation mechanism of these pyridyl–coinage metal complexes. Our study shows that C5H4N bonds to the metal clusters through a M–C σ bond and [Mm–C5H4N]− is produced via a stepwise mechanism. The first step is a direct insertion reaction between [Mm]− and C5H5N with activation of the C–H bond to yield the intermediate [HMm–C5H4N]−. The second step is H atom abstraction by a neutral metal atom to yield [Mm–C5H4N]−.

Photodetachment of group 11 cyanide anions MCN− (M = Cu, Ag, Au) has been investigated using photoelectron velocity-map imaging. The electron affinities (EAs) of CuCN (1.468(26)) and AgCN (1.602(22)) are larger, while that of AuCN (2.066(8)) is smaller than those of the free atoms. This intriguing observation was confirmed by theoretical studies and was assigned to the transition between ionic and covalent bond properties. The harmonic frequencies of the extended vibrational progressions in the M−C stretching mode are 460(50), 385(27), and 502(10) cm−1, respectively, which suggests a stronger bond for Au−CN than for Ag−CN. Electronic structure analysis and model calculations suggest that all M-C bonds in group 11 cyanides are best described as single bonds. A model has been proposed to explain how the relativistic effects influence the Au−C bond strength in AuCN.

For the comprehensive analysis of organic compounds, especially thermal labile and nonpolar compounds, an electrospray/vacuum ultraviolet (VUV) single-photon ionization (ES-SPI) method was developed. The fine droplets of the sample solution from the electrospray process were directed through a quartz capillary and two skimmers to form a molecular beam into a high vacuum ionization chamber. The neutral sample molecules were softly ionized with tunable VUV light and analyzed with a reflection time-of-flight mass spectrometer (RTOF-MS). The ionization energy (IE) and appearance onsets of fragments were obtained based on the photoionization efficiency (PIE) spectrum. The isomers can also be distinguished. With this new method, clean (fragment-free) mass spectra of nonpolar compounds, such as benzene, cyclohexane, and some thermal labile solid compounds (triphenylamine, thioacetamide, and urea) have been obtained without any tedious pretreatment. The components of complex mixtures (gasoline and kerosene) can be identified. Furthermore, quantitative analysis of the components can be obtained based on photoionization cross section data. This method may be used for quantitative analysis of small biomolecules and natural products.

Structures and electronic properties of the mixed metal hydride anions AuAgH−, Au2AgH−, AuAg2H− and their neutrals are studied using anionic photoelectron imaging and theoretical calculations. The three isomers of AuAgH− are determined to be linear and those of AuAgH are determined to have Cs symmetry. The structures of Au2AgH−, AuAg2H− and their corresponding neutrals are determined to be planar with Cs or C2v symmetries. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these anions are reported. Similar to the homonuclear Aum− and Agn− clusters, the metal hydride anions with an even number of valence electrons have higher VDEs than those with an odd number. Variation of the VDEs of these metal hydride anions with interchange of Au, Ag and H (for example AumAgn− → Aum−1Agn+ 1−, or Aum−1AgnH−) will be shown to be characterized by the electronegativities of Au, Ag and H. The results presented in this study provide important insights into the similar and different characteristics of these three elements in small clusters.

We have combined photoelectron velocity-map imaging (VMI) spectroscopy and theoretical calculations to elucidate the geometry and energy properties of Aux−(Solv)n clusters with x = 1, 2; n = 1, 2; and Solv = H2O and CH3OH. Besides the blue-shifted vertical electron detachment energies (VDEs) of the complexes Au1,2−(Solv)n with the increase of the solvation number (n), we independently probed two distinct Au−(CH3OH)2 isomers, which combined with MP2/aug-cc-pVTZ(pp) calculations represent a competition between O⋯H–O hydrogen bonds (HBs) and Au⋯H–O nonconventional hydrogen bonds (NHBs). Complementary calculations provide the total binding energies of the low-energy isomers. Moreover, the relationship between the total binding energies and total VDEshift is discussed. We found that the Au1,2− anions exhibit halide-analogous behavior in microsolvation. These findings also demonstrate that photoelectron velocity map imaging spectroscopy with the aid of the ab initio calculations is an effective tool for investigating weak-interaction complexes.

M(N2)n+ (M = Y, La, Ce; n = 7–8) complexes have been studied by infrared photodissociation (IRPD) spectroscopy and density functional theory (DFT) calculations. The experimental results indicate that the N–N stretching vibrational frequencies are red-shifted from the gas-phase N2 value. The π back-donation is found to be a main contributor in these systems. IRPD spectra and DFT calculations reveal the coexistence of two isomers in the seven-coordinate M(N2)7+ and eight-coordinate M(N2)8+ complexes, respectively. The present studies on these metal–nitrogen complexes shed light on the interactions and coordinations toward N2 with transition and lanthanide metals.

Activation of the C–H bond of pyridine by [Mm]− (M = Cu, Ag, Au, m = 1–3) is investigated by experiment and theory. Complexes of coinage metal clusters and the pyridyl group, [Mm–C5H4N]−, are produced from reactions between metal clusters formed by laser ablation of coinage metal samples and pyridine molecules seeded in argon carrier gas. We examine the structure and formation mechanism of these pyridyl–coinage metal complexes. Our study shows that C5H4N bonds to the metal clusters through a M–C σ bond and [Mm–C5H4N]− is produced via a stepwise mechanism. The first step is a direct insertion reaction between [Mm]− and C5H5N with activation of the C–H bond to yield the intermediate [HMm–C5H4N]−. The second step is H atom abstraction by a neutral metal atom to yield [Mm–C5H4N]−.