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Cheng YY, Cui CX. Theoretical study on hydrogen transfer in the dissociation of dimethyl disulfide radical cations. Phys Chem Chem Phys 2023; 25:3780-3788. [PMID: 36644933 DOI: 10.1039/d2cp05395k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Hydrogen transfer (HT) is of crucial importance in biochemistry and atmospheric chemistry. Here, HT processes involved in the dissociation reaction of dimethyl disulfide radical cations (DMDS˙+, CH3SSCH3˙+) are investigated using quantum chemical calculations. Four HTs from the C to S atom and one HT from the S to S atom are observed and the most probable paths are proposed in the dissociation channel from DMDS˙+ to CHnS+ (n = 2-4). The mechanisms of all these five HTs are described as hydrogen atom transfer (HAT) and four of them are accompanied by electron transfer (ET). Considering the catalytic effect of water molecules existing in organisms and the atmosphere, five HT processes in the dissociation of the [DMDS + H2O]˙+ complex are further explored, which show lower free energy barriers. With the participation of water molecules acting as a base, two HTs from the C to the S atom, which have the largest decrease in energy barriers, are characterized as concerted proton-coupled electron transfer (cPCET). These results can be extended to understand the mechanism of the HT process during the dissociation of disulfide and help provide a strategy to design a rare cPCET mechanism for the activation of the C-H bond.
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Affiliation(s)
- Yuan-Yuan Cheng
- Jiangxi Key Laboratory for Mass Spectrometry and Instrumentation, East China University of Technology, Nanchang, China.
| | - Cheng-Xing Cui
- School of Chemistry and Chemical Engineering, Henan Institute of Science and Technology, Xinxiang, China.
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2
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Ochmann M, Hussain A, von Ahnen I, Cordones AA, Hong K, Lee JH, Ma R, Adamczyk K, Kim TK, Schoenlein RW, Vendrell O, Huse N. UV-Photochemistry of the Disulfide Bond: Evolution of Early Photoproducts from Picosecond X-ray Absorption Spectroscopy at the Sulfur K-Edge. J Am Chem Soc 2018; 140:6554-6561. [PMID: 29771112 DOI: 10.1021/jacs.7b13455] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We have investigated dimethyl disulfide as the basic moiety for understanding the photochemistry of disulfide bonds, which are central to a broad range of biochemical processes. Picosecond time-resolved X-ray absorption spectroscopy at the sulfur K-edge provides unique element-specific insight into the photochemistry of the disulfide bond initiated by 267 nm femtosecond pulses. We observe a broad but distinct transient induced absorption spectrum which recovers on at least two time scales in the nanosecond range. We employed RASSCF electronic structure calculations to simulate the sulfur-1s transitions of multiple possible chemical species, and identified the methylthiyl and methylperthiyl radicals as the primary reaction products. In addition, we identify disulfur and the CH2S thione as the secondary reaction products of the perthiyl radical that are most likely to explain the observed spectral and kinetic signatures of our experiment. Our study underscores the importance of elemental specificity and the potential of time-resolved X-ray spectroscopy to identify short-lived reaction products in complex reaction schemes that underlie the rich photochemistry of disulfide systems.
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Affiliation(s)
- Miguel Ochmann
- Department of Physics , University of Hamburg and Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science , 22761 Hamburg , Germany
| | - Abid Hussain
- Department of Physics , University of Hamburg and Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science , 22761 Hamburg , Germany
| | - Inga von Ahnen
- Department of Physics , University of Hamburg and Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science , 22761 Hamburg , Germany
| | - Amy A Cordones
- Ultrafast X-ray Science Lab, Chemical Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Kiryong Hong
- Department of Chemistry and Chemistry Institute of Functional Materials , Pusan National University , Busan 46241 , South Korea
| | - Jae Hyuk Lee
- Ultrafast X-ray Science Lab, Chemical Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Rory Ma
- Department of Chemistry and Chemistry Institute of Functional Materials , Pusan National University , Busan 46241 , South Korea
| | - Katrin Adamczyk
- Department of Physics , University of Hamburg and Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science , 22761 Hamburg , Germany
| | - Tae Kyu Kim
- Department of Chemistry and Chemistry Institute of Functional Materials , Pusan National University , Busan 46241 , South Korea
| | - Robert W Schoenlein
- Ultrafast X-ray Science Lab, Chemical Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Oriol Vendrell
- Center for Free-Electron Laser Science , DESY and The Hamburg Centre for Ultrafast Imaging , 22607 Hamburg , Germany
| | - Nils Huse
- Department of Physics , University of Hamburg and Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science , 22761 Hamburg , Germany
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Kazuma E, Jung J, Ueba H, Trenary M, Kim Y. Direct Pathway to Molecular Photodissociation on Metal Surfaces Using Visible Light. J Am Chem Soc 2017; 139:3115-3121. [PMID: 28170245 DOI: 10.1021/jacs.6b12680] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We demonstrate molecular photodissociation on single-crystalline metal substrates, driven by visible-light irradiation. The visible-light-induced photodissociation on metal substrates has long been thought to never occur, either because visible-light energy is much smaller than the optical energy gap between the frontier electronic states of the molecule or because the molecular excited states have short lifetimes due to the strong hybridization between the adsorbate molecular orbitals (MOs) and metal substrate. The S-S bond in dimethyl disulfide adsorbed on both Cu(111) and Ag(111) surfaces was dissociated through direct electronic excitation from the HOMO-derived MO (the nonbonding lone-pair type orbitals on the S atoms (nS)) to the LUMO-derived MO (the antibonding orbital localized on the S-S bond (σ*SS)) by irradiation with visible light. A combination of scanning tunneling microscopy and density functional theory calculations revealed that visible-light-induced photodissociation becomes possible due to the interfacial electronic structures constructed by the hybridization between molecular orbitals and the metal substrate states. The molecule-metal hybridization decreases the gap between the HOMO- and LUMO-derived MOs into the visible-light energy region and forms LUMO-derived MOs that have less overlap with the metal substrate, which results in longer excited-state lifetimes.
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Affiliation(s)
- Emiko Kazuma
- Surface and Interface Science Laboratory, RIKEN , Wako, Saitama 351-0198, Japan
| | - Jaehoon Jung
- Department of Chemistry, University of Ulsan , 93 Daehak-ro, Nam-gu, Ulsan 680-749, Republic of Korea
| | - Hiromu Ueba
- Graduate School of Science and Engineering, University of Toyama , Toyama 930-8555, Japan
| | - Michael Trenary
- Department of Chemistry, University of Illinois at Chicago , 845 West Taylor Street, Chicago, Illinois 60607, United States
| | - Yousoo Kim
- Surface and Interface Science Laboratory, RIKEN , Wako, Saitama 351-0198, Japan
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4
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Cole-Filipiak NC, Shapero M, Haibach-Morris C, Neumark DM. Production and Photodissociation of the Methyl Perthiyl Radical. J Phys Chem A 2016; 120:4818-26. [PMID: 26859337 DOI: 10.1021/acs.jpca.5b12284] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The photodissociation dynamics of the methyl perthiyl (CH3SS) radical are investigated via molecular beam photofragment translational spectroscopy, using "soft" electron ionization to detect the radicals and their photofragments. With this new capability, we have shown that CH3SS can be generated from flash pyrolysis of dimethyl trisulfide. Utilizing this source of radicals and the advantages afforded by soft electron ionization, we have reinvestigated the photodissociation dynamics of CH3SS at 248 nm, finding CH3S + S to be the dominant dissociation channel with CH3 + SS as a minor process. These results differ from previous work reported in our laboratory in which we found CH3 + SS and CH2S + SH as the main dissociation channels. The difference in results is discussed in light of our new capabilities for characterization of radical production.
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Affiliation(s)
- Neil C Cole-Filipiak
- Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.,Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Mark Shapero
- Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.,Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Courtney Haibach-Morris
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Daniel M Neumark
- Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.,Department of Chemistry, University of California , Berkeley, California 94720, United States
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Harrison AW, Ryazanov M, Sullivan EN, Neumark DM. Photodissociation dynamics of the methyl perthiyl radical at 248 and 193 nm using fast-beam photofragment translational spectroscopy. J Chem Phys 2016; 145:024305. [PMID: 27421403 DOI: 10.1063/1.4955195] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The photodissociation dynamics of the methyl perthiyl radical (CH3SS) have been investigated using fast-beam coincidence translational spectroscopy. Methyl perthiyl radicals were produced by photodetachment of the CH3SS(-) anion followed by photodissociation at 248 nm (5.0 eV) and 193 nm (6.4 eV). Photofragment mass distributions and translational energy distributions were measured at each dissociation wavelength. Experimental results show S atom loss as the dominant (96%) dissociation channel at 248 nm with a near parallel, anisotropic angular distribution and translational energy peaking near the maximal energy available to ground state CH3S and S fragments, indicating that the dissociation occurs along a repulsive excited state. At 193 nm, S atom loss remains the major fragmentation channel, although S2 loss becomes more competitive and constitutes 32% of the fragmentation. The translational energy distributions for both channels are very broad at this wavelength, suggesting the formation of the S2 and S atom products in several excited electronic states.
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Affiliation(s)
- Aaron W Harrison
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Mikhail Ryazanov
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Erin N Sullivan
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Daniel M Neumark
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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Yan L, Wenliang W, Zhongwen L, Hongjiang R. Kinetics investigation of the hydrogen abstraction reaction between CH3SS and CN radicals. J Mol Model 2016; 22:36. [PMID: 26781664 DOI: 10.1007/s00894-015-2905-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 12/28/2015] [Indexed: 11/30/2022]
Abstract
The reaction mechanisms and rates for the H abstraction reactions between CH3SS and CN radicals in the gas phase were investigated with density functional theory (DFT) methods. The geometries, harmonic vibrational frequencies, and energies of all stationary points were obtained at B3PW91/6-311G(d,p) level of theory. Relationships between the reactants, intermediates, transition states and products were confirmed, with the frequency and the intrinsic reaction coordinate (IRC) analysis at the same theoretical level. High accurate energy information was provided by the G3(MP2) method combined with the standard statistical thermodynamics. Gibbs free energies at 298.15 K for all of the reaction steps were reported, and were used to describe the profile diagrams of the potential energy surface. The rate constants were evaluated with both the classical transition state theory and the canonical variational transition state theory, in which the small-curvature tunneling correction was included. A total number of 9 intermediates (IMs) and 17 transition states (TSs) were obtained. It is shown that IM1 is the most stable intermediate by the largest energy release, and the channel of CH3SS + CN → IM3 → TS10 → P1(CH2SS + HCN) is the dominant reaction with the lowest energy barrier of 144.7 kJ mol(-1). The fitted Arrhenius expressions of the calculated CVT/SCT rate constants for the rate-determining step of the favorable channel is k =7.73 × 10(6) T (1.40)exp(-14,423.8/T) s(-1) in the temperature range of 200-2000 K. The apparent activation energy E a(app.) for the main channel is -102.5 kJ mol(-1), which is comparable with the G3(MP2) energy barrier of -91.8 kJ mol(-1) of TS10 (relative to the reactants).
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Affiliation(s)
- Liu Yan
- School of Chemistry and Chemical Engineering, Key Laboratory for Macromolecular Science of Shaanxi Province, Shaanxi Normal University, Xi'an, Shaanxi, 710062, People's Republic of China.
- College of Chemistry and Environment, Shaanxi Engineering Research Center of Coal Conversion Alcohol, Weinan Normal University, Weinan, Shaanxi, 714099, People's Republic of China.
| | - Wang Wenliang
- School of Chemistry and Chemical Engineering, Key Laboratory for Macromolecular Science of Shaanxi Province, Shaanxi Normal University, Xi'an, Shaanxi, 710062, People's Republic of China
| | - Liu Zhongwen
- School of Chemistry and Chemical Engineering, Key Laboratory for Macromolecular Science of Shaanxi Province, Shaanxi Normal University, Xi'an, Shaanxi, 710062, People's Republic of China
| | - Ren Hongjiang
- School of Chemistry and Chemical Engineering, Xi'an University, Xi'an, Shaanxi, 710065, People's Republic of China
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Straus DB, Butler LM, Alligood BW, Butler LJ. Analyzing angular distributions for two-step dissociation mechanisms in velocity map imaging. J Phys Chem A 2013; 117:7102-6. [PMID: 23464815 DOI: 10.1021/jp400368f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Increasingly, velocity map imaging is becoming the method of choice to study photoinduced molecular dissociation processes. This paper introduces an algorithm to analyze the measured net speed, P(vnet), and angular, β(vnet), distributions of the products from a two-step dissociation mechanism, where the first step but not the second is induced by absorption of linearly polarized laser light. Typically, this might be the photodissociation of a C-X bond (X = halogen or other atom) to produce an atom and a momentum-matched radical that has enough internal energy to subsequently dissociate (without the absorption of an additional photon). It is this second step, the dissociation of the unstable radicals, that one wishes to study, but the measured net velocity of the final products is the vector sum of the velocity imparted to the radical in the primary photodissociation (which is determined by taking data on the momentum-matched atomic cophotofragment) and the additional velocity vector imparted in the subsequent dissociation of the unstable radical. The algorithm allows one to determine, from the forward-convolution fitting of the net velocity distribution, the distribution of velocity vectors imparted in the second step of the mechanism. One can thus deduce the secondary velocity distribution, characterized by a speed distribution P(v1,2°) and an angular distribution I(θ2°), where θ2° is the angle between the dissociating radical's velocity vector and the additional velocity vector imparted to the product detected from the subsequent dissociation of the radical.
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Affiliation(s)
- Daniel B Straus
- Department of Chemistry and the James Franck Institute, University of Chicago, Chicago, Illinois 60637, USA
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9
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Cole-Filipiak NC, Negru B, Just GMP, Park D, Neumark DM. Photodissociation dynamics of the methyl perthiyl radical at 248 nm via photofragment translational spectroscopy. J Chem Phys 2013; 138:054301. [PMID: 23406113 DOI: 10.1063/1.4789485] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Neil C Cole-Filipiak
- Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, USA
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10
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Chichinin AI, Gericke KH, Kauczok S, Maul C. Imaging chemical reactions – 3D velocity mapping. INT REV PHYS CHEM 2009. [DOI: 10.1080/01442350903235045] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Brouard M, Campbell EK, Johnsen AJ, Vallance C, Yuen WH, Nomerotski A. Velocity map imaging in time of flight mass spectrometry. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2008; 79:123115. [PMID: 19123553 DOI: 10.1063/1.3036978] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A new variation on time of flight mass spectrometry is presented, which uses a fast framing charge coupled device camera to velocity map image multiple product masses in a single acquisition. The technique is demonstrated on two photofragmentation processes, those of CS(2) and CH(3)S(2)CH(3) (dimethyldisulfide) at a photolysis wavelength of 193 nm. In both cases, several mass fragments are imaged simultaneously, and speed distributions and anisotropy parameters are extracted that are comparable to those obtained by imaging each fragment separately in conventional velocity map imaging studies.
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Affiliation(s)
- M Brouard
- The Department of Chemistry, The Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
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12
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Brouard M, Green AV, Quadrini F, Vallance C. Photodissociation dynamics of OCS at 248nm: The S(D21) atomic angular momentum polarization. J Chem Phys 2007; 127:084304. [PMID: 17764245 DOI: 10.1063/1.2757618] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The dissociation of OCS has been investigated subsequent to excitation at 248 nm. Speed distributions, speed dependent translational anisotropy parameters, angular momentum alignment, and orientation are reported for the channel leading to S((1)D(2)). In agreement with previous experiments, two product speed regimes have been identified, correlating with differing degrees of rotational excitation in the CO coproducts. The velocity dependence of the translational anisotropy is also shown to be in agreement with previous work. However, contrary to previous interpretations, the speed dependence is shown to primarily reflect the effects of nonaxial recoil and to be consistent with predominant excitation to the 2 (1)A(') electronic state. It is proposed that the associated electronic transition moment is polarized in the molecular plane, at an angle greater than approximately 60 degrees to the initial linear OCS axis. The atomic angular momentum polarization data are interpreted in terms of a simple long-range interaction model to help identify likely surfaces populated during dissociation. Although the model neglects coherence between surfaces, the polarization data are shown to be consistent with the proposed dissociation mechanisms for the two product speed regimes. Large values for the low and high rank in-plane orientation parameters are reported. These are believed to be the first example of a polyatomic system where these effects are found to be of the same order of magnitude as the angular momentum alignment.
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Affiliation(s)
- M Brouard
- The Physical and Theoretical Chemistry Laboratory, The Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
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Brouard M, Quadrini F, Vallance C. The photodissociation dynamics of OCS at 248nm: The S(PJ3) atomic angular momentum polarization. J Chem Phys 2007; 127:084305. [PMID: 17764246 DOI: 10.1063/1.2757619] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The dissociation of OCS has been investigated subsequent to excitation at 248 nm using velocity map ion imaging. Speed distributions, speed dependent translational anisotropy parameters, and the atomic angular momentum orientation and alignment are reported for the channel leading to S((3)P(J)). The speed distributions and beta parameters are in broad agreement with previous work and show behavior that is highly sensitive to the S-atom spin-orbit state. The data are shown to be consistent with the operation of at least two triplet production mechanisms. Interpretation of the angular momentum polarization data in terms of an adiabatic picture has been used to help identify a likely dissociation pathway for the majority of the S((3)P(J)) products, which strongly favors production of J=2 fragment atoms, correlated, it is proposed, with rotationally hot and vibrationally cold CO cofragments. For these fragments, optical excitation to the 2 (1)A(') surface is thought to constitute the first step, as for the singlet dissociation channel. This is followed by crossing, via a conical intersection, to the ground 1 (1)A(') state, from where intersystem crossing occurs, populating the 1 (3)A(')1 (3)A(")((3)Pi) states. The proposed mechanism provides a qualitative rationale for the observed spin-orbit populations, as well as the S((3)P(J)) quantum yield and angular momentum polarization. At least one other production mechanism, leading to a more statistical S-atom spin-orbit state distribution and rotationally cold, vibrationally hot CO cofragments, is thought to involve direct excitation to either the (3)Sigma(-) or (3)Pi states.
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Affiliation(s)
- M Brouard
- The Physical and Theoretical Chemistry Laboratory, The Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
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Brouard M, Cireasa R, Clark AP, Groenenboom GC, Hancock G, Horrocks SJ, Quadrini F, Ritchie GAD, Vallance C. The photodissociation dynamics of ozone at 193nm: An O(D21) angular momentum polarization study. J Chem Phys 2006; 125:133308. [PMID: 17029461 DOI: 10.1063/1.2210009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Polarized laser photolysis, coupled with resonantly enhanced multiphoton ionization detection of O(1D2) and velocity-map ion imaging, has been used to investigate the photodissociation dynamics of ozone at 193 nm. The use of multiple pump and probe laser polarization geometries and probe transitions has enabled a comprehensive characterization of the angular momentum polarization of the O(1D2) photofragments, in addition to providing high-resolution information about their speed and angular distributions. Images obtained at the probe laser wavelength of around 205 nm indicate dissociation primarily via the Hartley band, involving absorption to, and diabatic dissociation on, the B 1B2(3 1A1) potential energy surface. Rather different O(1D2) speed and electronic angular momentum spatial distributions are observed at 193 nm, suggesting that the dominant excitation at these photon energies is to a state of different symmetry from that giving rise to the Hartley band and also indicating the participation of at least one other state in the dissociation process. Evidence for a contribution from absorption into the tail of the Hartley band at 193 nm is also presented. A particularly surprising result is the observation of nonzero, albeit small values for all three rank K = 1 orientation moments of the angular momentum distribution. The polarization results obtained at 193 and 205 nm, together with those observed previously at longer wavelengths, are interpreted using an analysis of the long range quadrupole-quadrupole interaction between the O(1D2) and O2(1Deltag) species.
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Affiliation(s)
- M Brouard
- The Physical and Theoretical Chemistry Laboratory, The Department of Chemistry, University of Oxford, Oxford OX1 3QZ, United Kingdom.
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15
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Brouard M, Cireasa R, Clark AP, Preston TJ, Vallance C. The photodissociation dynamics of NO2 at 308nm and of NO2 and N2O4 at 226nm. J Chem Phys 2006; 124:64309. [PMID: 16483209 DOI: 10.1063/1.2166631] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Velocity-map ion imaging has been applied to the photodissociation of NO(2) via the first absorption band at 308 nm using (2 + 1) resonantly enhanced multiphoton ionization detection of the atomic O((3)P(J)) products. The resulting ion images have been analyzed to provide information about the speed distribution of the O((3)P(J)) products, the translational anisotropy, and the electronic angular momentum alignment. The atomic speed distributions were used to provide information about the internal quantum-state distribution in the NO coproducts. The data were found to be consistent with an inverted NO vibrational quantum-state distribution, and thereby point to a dynamical, as opposed to a statistical dissociation mechanism subsequent to photodissociation at 308 nm. Surprisingly, at this wavelength the O-atom electronic angular momentum alignment was found to be small. Probe-only ion images obtained under a variety of molecular-beam backing-pressure conditions, and corresponding to O atoms generated in the photodissociation of either the monomer, NO(2), or the dimer, N(2)O(4), at 226 nm, are also reported. For the monomer, where 226 nm corresponds to excitation into the second absorption band, the kinetic-energy release distributions are also found to indicate a strong population inversion in the NO cofragment, and are shown to be remarkably similar to those previously observed in the wavelength range of 193-248 nm. Mechanistic implications of this result are discussed. At 226 nm it has also been possible to observe directly O atoms from the photodissociation of the dimer. The O-atom velocity distribution has been analyzed to provide information about its production mechanism.
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Affiliation(s)
- M Brouard
- The Physical and Theoretical Chemistry Laboratory, The Department of Chemistry, University of Oxford, UK.
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Ashfold MNR, Nahler NH, Orr-Ewing AJ, Vieuxmaire OPJ, Toomes RL, Kitsopoulos TN, Garcia IA, Chestakov DA, Wu SM, Parker DH. Imaging the dynamics of gas phase reactions. Phys Chem Chem Phys 2006; 8:26-53. [PMID: 16482242 DOI: 10.1039/b509304j] [Citation(s) in RCA: 240] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ion imaging methods are making ever greater impact on studies of gas phase molecular reaction dynamics. This article traces the evolution of the technique, highlights some of the more important breakthroughs with regards to improving image resolution and in image processing and analysis methods, and then proceeds to illustrate some of the many applications to which the technique is now being applied--most notably in studies of molecular photodissociation and of bimolecular reaction dynamics.
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18
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Bass MJ, Brouard M, Cireasa R, Clark AP, Vallance C. Imaging photon-initiated reactions: A study of the Cl(P3∕22)+CH4→HCl+CH3 reaction. J Chem Phys 2005; 123:94301. [PMID: 16164339 DOI: 10.1063/1.2009737] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The hydrogen or deuterium atom abstraction reactions between Cl((2)P(3/2)) and methane, or its deuterated analogues CD(4) and CH(2)D(2), have been studied at mean collision energies around 0.34 eV. The experiments were performed in a coexpansion of molecular chlorine and methane in helium, with the atomic Cl reactants generated by polarized laser photodissociation of Cl(2) at 308 nm. The Cl-atom reactants and the methyl radical products were detected using (2+1) resonantly enhanced multiphoton ionization, coupled with velocity-map ion imaging. Analysis of the ion images reveals that in single-beam experiments of this type, careful consideration must be given to the spread of reagent velocities and collision energies. Using the reactions of Cl with CH(4), CD(4), and CH(2)D(2), as examples, it is shown that the data can be fitted well if the reagent motion is correctly described, and the angular scattering distributions can be obtained with confidence. New evidence is also provided that the CD(3) radicals from the Cl+CD(4) reaction possess significant rotational alignment under the conditions of the present study. The results are compared with previous experimental and theoretical works, where these are available.
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Affiliation(s)
- M J Bass
- The Physical and Theoretical Chemistry Laboratory, The Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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