Li Wang

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Organization: Dalian Institute of Chemical Physics

Department: State Key Laboratory of Molecular Reaction Dynamics

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Polymer

Stimuli Responsive Polymers PH Responsive Polymers Stimuli Responsive Polymers PH Responsive Polymers Temperature Responsive Polymers

Chemicals
References

Vacuum Ultraviolet Photon Ionization Mass Spectrometer for Detection of Dioxin Precursors

Co-reporter:Ben-Kang LIU, Liang CHEN, Yan-Qiu WANG, Zhe SONG, Li WANG

Chinese Journal of Analytical Chemistry 2014 Volume 42(Issue 2) pp:173-178

Publication Date(Web):February 2014

DOI:10.1016/S1872-2040(13)60708-2

Waste incineration is considered as a main source of dioxins. During the generation of dioxins, dioxin precursors, such as polychlorinated benzenes (PCBz), polychlorinated phenols (PCPh), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) etc. have been proved to be produced with much higher concentrations than dioxins, which are determined to be closely related to dioxin toxic equivalents. Therefore, online monitoring of these precursor compounds has been becoming one of the main research directions of dioxin detection. In this study, a novel method for online detection of these dioxin precursors in gas phase was developed by nanosecond vacuum ultraviolet single photon ionization technique, combined with time-of-flight mass spectrometer. This setup was evaluated by monitoring chlorobenzene, polychlorinated phenols and naphthalene in gas phase. The results show that there is a linear relation between the parent ion intensity and the chlorobenzene concentration ranged from 5 ppb to 100 ppb.Nanosecond vacuum ultraviolet (VUV, 118 nm) by frequency tripling of the 3rd harmonic output of a YAG laser in xenon/argon mixture was optimized. The VUV single photon ionization technique, combined with time-of-flight mass spectrometer, was developed for monitoring chlorobenzene. Linear dependence of the ion intensity on the concentration in the range of 5–100 ppb was obtained.

Femtosecond Photodetachment of Silver Anions

Co-reporter:Benkang Liu, Tao Long, Yanqiu Wang, and Li Wang

The Journal of Physical Chemistry A 2013 Volume 117(Issue 44) pp:11210-11216

Publication Date(Web):October 10, 2013

DOI:10.1021/jp405018r

The two- and three-photon detachment of negative silver ions in a femtosecond infrared laser field is studied using photoelectron velocity map imaging methods. Photoelectron angular distributions (PADs) are obtained for these detachment channels; these PADs change dramatically when the laser wavelength and intensity are changed. Theoretical predictions, which are based on the adiabatic Keldysh–Faisal–Reiss saddle point method, are in good agreement with our experiment. The dependence of the PAD on the laser wavelengths and intensities is due to the interference between the different partial wave functions. The relative contributions of the different partial waves to the detachment amplitude are altered by changing the laser parameters and, as a result, the shape of the PAD. Close to the detachment threshold, the two-photon detachment process also follows the Wigner threshold law. Near the detachment threshold, the large differences between the calculated results and our experimental results indicate that the ponderomotive energy shifts caused by the femtosecond laser fields must be taken into account in the theoretical model. The three-photon detachment of Ag– is also observed and compared with theoretical calculations.

Ultrafast dynamics of pyridine in “channel three” region

Co-reporter:Bingxing Wang, Benkang Liu, Yanqiu Wang, Li Wang

International Journal of Mass Spectrometry 2010 Volume 289(2–3) pp:92-97

Publication Date(Web):15 January 2010

DOI:10.1016/j.ijms.2009.09.014

The ultrafast dynamics of the S1 (nπ*) state of pyridine has been investigated by using femtosecond time-resolved mass spectrometry and photoelectron imaging combined with (1 + 2′) resonance-enhanced multiphoton ionization via the Rydberg states. Upon excitation into the channel-three region, an ultrafast decay process is observed with a lifetime of about 3.7 ps. The fragment ions show an additional ultrafast decay component. Time resolved photoelectron imaging experiments reveal the excited pyridine in channel three region relaxes to an optically dark state on this short time scale. According to previous experimental and theoretical results, we suggest tentatively the ultrafast channel is due to IVR induced fast internal conversion.Time-resolved photoelectron images (inverse-Abel transform) of pyridine taken at different pump–probe delay times. Femtosecond pump laser at 271.5 nm excites the molecules into the S1 state above the channel-three threshold. The time evolution of the prepared state is ionized by a delayed probe laser (407.1 nm).

Dynamics of Highly Excited Nitroaromatics

Co-reporter:Bingxing Wang, Benkang Liu, Yanqiu Wang, and Li Wang

The Journal of Physical Chemistry A 2010 Volume 114(Issue 50) pp:12972-12978

Publication Date(Web):November 23, 2010

DOI:10.1021/jp104727p

Although the photodissociation of nitroaromatics in low excitation electronic states has been extensively studied in recent decades, little is known about the highly excited electronic states. The fragmentation dynamics of three nitroaromatics, nitrobenzene, o-nitrotoluene, and m-nitrotoluene, in highly excited states, populated by the absorption of two photons at 271 nm, are studied with time-of-flight mass spectrometry. The temporal evolutions of the highly excited states are monitored by one-photon ionization at 408 nm. The transients of parent and fragment ions exhibit two ultrafast deactivation processes. The first process is ultrafast internal conversion from the initial excitation to Rydberg states in tens of femtoseconds. The second one is conversion from the Rydberg states to the vibrational manifold in the ground electronic states within hundreds of femtoseconds. The internal conversion process is accelerated by methyl substitution. In o-nitrotoluene, the two processes become much faster due to the hydrogen transfer from the CH3 to the NO2 group (ortho effect).

Ultrafast dynamics of chlorobenzene clusters

Co-reporter:Benkang Liu, Bingxing Wang, Yanqiu Wang, Li Wang

Chemical Physics Letters 2009 Volume 477(4–6) pp:266-270

Publication Date(Web):6 August 2009

DOI:10.1016/j.cplett.2009.07.025

Abstract

The ultrafast dynamics of chlorobenzene clusters upon 271 nm excitation is studied by femtosecond pump–probe time-of-flight mass spectrometry. Transient profiles of clusters are fitted by two-exponential decay component models, an ultrafast component and a slow decay component. The ultrafast (∼170 fs) decay of S₁ state is tentatively attributed to the internal conversion to the high vibrational levels of S₀ state. Lifetimes of this ultrafast component decease with the cluster size, due to the influence of the solvation effects, while lifetimes of the slow decay component (>1 ns) increase with the cluster size, due to the increase of freedom degrees.

Time-Resolved Dynamics of NO2 in Its Conical Intersection Region

Co-reporter:Benkang Liu, Jingyi Zhu, Bingxing Wang, Yanqiu Wang and Li Wang

The Journal of Physical Chemistry A 2009 Volume 113(Issue 50) pp:13839-13844

Publication Date(Web):October 14, 2009

DOI:10.1021/jp907041a

Photodissociation dynamics of NO2 in its conical intersection region have been explored experimentally on a real-time scale by time-of-flight mass spectrometry. Excited at 400.6 nm and probed by 801.6 nm femtosecond laser pulses, different dynamical behaviors of both the parent ion NO2+ and the fragment ion NO+ have been observed under parallel and perpendicular pump−probe laser polarization configurations. Distinct oscillations in NO2+ and NO+ signals are observed when laser polarizations of pump and probe are perpendicular to each other, whereas the oscillations become blurry when the laser polarizations are parallel. The observed transient signals imply that the dissociation mechanism of NO2 in the A2B2 excited state needed to be reconsidered. On the basis of our observation, Rydberg states play important roles in the ultrafast dissociation dynamics of NO2.

Home-made capillary array electrophoresis for high-throughput amino acid analysis

Co-reporter:Kaiying Liu, Hui Wang, Jiling Bai, Li Wang

Analytica Chimica Acta 2008 Volume 622(1–2) pp:169-174

Publication Date(Web):1 August 2008

DOI:10.1016/j.aca.2008.05.062

A capillary array electrophoresis (CAE) with confocal rotary scanner for high-throughput carboxytetramethylrhodamine succinimidyl ester (TAMRA)-labeled amino acid (AA) analysis is presented. Performance of the CAE setup was evaluated with AA samples. Up to 128 capillaries could be detected in parallel. For the first time, the device was applied to separate the enantiomers of isoleucine, cysteine, and glutamic acid with cyclodextrin-modified electrolytes by capillary zone electrophoresis. Baseline separation of seven AAs is also demonstrated using micellar electrokinetic chromatography method.

Alignment effects of NO in femtosecond laser field

Co-reporter:Wei Guo, Jingyi Zhu, Bingxing Wang, Yanqiu Wang, Li Wang

Chemical Physics Letters 2007 Volume 448(4–6) pp:173-177

Publication Date(Web):14 November 2007

DOI:10.1016/j.cplett.2007.10.016

The laser-induced alignment effects of NO in linearly polarized femtosecond laser field within the intensity order of 1014 W/cm2 at 820 nm have been investigated experimentally by using velocity mapping technique. The angular and velocity distributions of fragment ions with different charge numbers are measured. The alignment degrees increased with the charge numbers, and were nearly independent of the laser intensities. Our results indicate the geometric alignment dominates before the ionization of NO into NO2+, while the dynamic alignment of the molecular ions dominates after the ionization.Experiments on the laser-induced alignments of NO in linearly polarized femtosecond laser field within the intensity order of 1014 W/cm2 at 820 nm by using velocity mapping technique. The angular and velocity distributions of fragment ions with different charge numbers are measured. Laser-induced alignments of NO are studied by using ion imaging. The angular and velocity distributions are measured under different laser intensity.

Theoretical studies on the reactions of formaldehyde with OH and OH−

Co-reporter:Yuchao Zhao, Bingxing Wang, Haiyang Li, Li Wang

Journal of Molecular Structure: THEOCHEM 2007 Volume 818(1–3) pp:155-161

Publication Date(Web):30 September 2007

DOI:10.1016/j.theochem.2007.05.018

The titled reactions are theoretically studied at MP4 (SDTQ) level with 6-311++G(3df,3pd) basis set. All the possible reaction channels are considered for the first time. The most favorable reaction path in H2CO + OH is the channel of producing H2O, which is exothermic by −32.02 kcal/mol, in well agreement with reported experimental result. For H2CO + OH−, the most favorable reaction channel is for H2 molecule formation through several paths. The reaction channels for producing H2 molecule in the titled systems are proposed for the first time. H atom formation in H2CO + OH and hydrogen symmetric transition in H2CO + OH− is also evaluated at higher theory level than literatures.

Fragmentation of dimethyl ether in femtosecond intense field

Co-reporter:Jingyi Zhu, Wei Guo, Yanqiu Wang, Li Wang

Chemical Physics 2006 Volume 326(2–3) pp:571-576

Publication Date(Web):1 August 2006

DOI:10.1016/j.chemphys.2006.03.020

Abstract

The fragmentation of dimethyl ether (DME) in intense femtosecond laser field has been studied at 810, 405 and 270 nm with intensities up to 2.48 × 10¹⁵, 3.86 × 10¹⁵ and 1.62 × 10¹⁴ W/cm², respectively. At 405 nm, DME is possibly firstly ionized by multiphoton absorption, and then parent ion DME⁺ dissociates into fragments via filed-induced dissociation. For 810 and 270 nm laser fields, DME firstly dissociates into CH₃O and CH₃ fragments and then these neutral fragments are ionized by field tunneling. Another possible way for DME to dissociate at 810 and 270 nm is that DME is ionized by intense field ejection of inner valance electron and then the excited DME⁺ dissociates into fragment ions. Ultrafast rearrangement of DME or DME⁺ in intense field may be responsible to the unpredictable fragment ions, ${CHO}^{+} / C_{2} H_{5}^{+} and H_{2}^{+}$ .

Capillary array electrophoresis for the research of asymmetric transformation reaction of L-proline to D-proline

Co-reporter:Jun Wang;Kaiying Liu;Guangming Sun;Jiling Bai

Journal of Separation Science 2005 Volume 28(Issue 18) pp:2551-2554

Publication Date(Web):4 NOV 2005

DOI:10.1002/jssc.200500260

One asymmetric transformation reaction of L-proline (L-Pro) to D-proline was studied by a home-made capillary array electrophoresis (CAE) for the first time. The aldehyde catalysts and the organic acid solvents for the asymmetric transformation reaction were rapidly screened and the enantiomeric excess values of the asymmetric product of L-Pro were directly obtained from the electrophoretogram of CAE.