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Heald LF, Gosman RS, Rotteger CH, Jarman CK, Sayres SG. Nonadiabatic Photodissociation and Dehydrogenation Dynamics of n-Butyl Bromide Following p-Rydberg Excitation. J Phys Chem Lett 2023:6278-6285. [PMID: 37399455 DOI: 10.1021/acs.jpclett.3c01438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/05/2023]
Abstract
Femtosecond time-resolved mass spectrometry, correlation mapping, and density functional theory calculations are employed to reveal the mechanism of C═C and C≡C formation (and related H2 production) following excitation to the p-Rydberg states of n-butyl bromide. Ultrafast pump-probe mass spectrometry shows that nonadiabatic relaxation operates as a multistep process reaching an intermediate state within ∼500 fs followed by relaxation to a final state within 10 ps of photoexcitation. Absorption of three ultraviolet photons accesses the dense p-Rydberg state manifold, which is further excited by the probe beam for C─C bond dissociation and dehydrogenation reactions. Rapid internal conversion deactivates the dehydrogenation pathways, while activating carbon backbone dissociation pathways. Thus, unsaturated carbon fragments decay with the lifetime of p-Rydberg (∼500 fs), matching the growth recorded in saturated hydrocarbon fragments. The saturated hydrocarbon signals subsequently decay on the picosecond time scale as the molecule relaxes below the Rydberg states and into halogen release channels.
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Affiliation(s)
- Lauren F Heald
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
- Biodesign Center for Applied Structural Discovery, Arizona State University, Tempe, Arizona 85287, United States
| | - Robert S Gosman
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
- Biodesign Center for Applied Structural Discovery, Arizona State University, Tempe, Arizona 85287, United States
| | - Chase H Rotteger
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
- Biodesign Center for Applied Structural Discovery, Arizona State University, Tempe, Arizona 85287, United States
| | - Carter K Jarman
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
- Biodesign Center for Applied Structural Discovery, Arizona State University, Tempe, Arizona 85287, United States
| | - Scott G Sayres
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
- Biodesign Center for Applied Structural Discovery, Arizona State University, Tempe, Arizona 85287, United States
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2
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Campbell JS, Nauta K, Hansen CS, Kable SH. POPTARTS: A New Method to Determine Quantum Yields in a Molecular Beam. J Phys Chem A 2022; 126:9268-9275. [DOI: 10.1021/acs.jpca.2c06289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Affiliation(s)
- Jyoti S. Campbell
- School of Chemistry, University of New South Wales, Kensington, NSW2052, Australia
| | - Klaas Nauta
- School of Chemistry, University of New South Wales, Kensington, NSW2052, Australia
| | | | - Scott H. Kable
- School of Chemistry, University of New South Wales, Kensington, NSW2052, Australia
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3
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Ashfold MNR, Ingle RA, Karsili TNV, Zhang J. Photoinduced C–H bond fission in prototypical organic molecules and radicals. Phys Chem Chem Phys 2019; 21:13880-13901. [DOI: 10.1039/c8cp07454b] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We survey and assess current knowledge regarding the primary photochemistry of hydrocarbon molecules and radicals.
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Affiliation(s)
| | | | | | - Jingsong Zhang
- Department of Chemistry
- University of California at Riverside
- Riverside
- USA
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4
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A measurement of the photoionization cross section of CH2Cl via photofragment translational spectroscopy of dichloromethane. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.09.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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5
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Scrape PG, Roberts TD, Lee SH, Butler LJ. Dissociation Pathways of the CH2CH2ONO Radical: NO2 + Ethene, NO + Oxirane, and a Non-Intrinsic Reaction Coordinate HNO + Vinoxy Pathway. J Phys Chem A 2016; 120:4973-87. [PMID: 27124098 DOI: 10.1021/acs.jpca.5b12669] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We first characterize the dissociation pathways of BrCH2CH2ONO, a substituted alkyl nitrite, upon photoexcitation at 193 nm under collision-free conditions, in a crossed laser-molecular beam scattering apparatus using vacuum ultraviolet photoionization detection. Three primary photodissociation pathways occur: photoelimination of HNO, leading to the products HNO + BrCH2CHO; C-Br bond photofission, leading to Br + CH2CH2ONO; and O-NO bond photofission, leading to NO + BrCH2CH2O. The data show that alkyl nitrites can eliminate HNO via a unimolecular mechanism in addition to the commonly accepted bulk disproportionation mechanism. Some of the products from the primary photodissociation pathways are highly vibrationally excited, so we then probe the product branching from the unimolecular dissociation of these unstable intermediates. Notably, the vibrationally excited CH2CH2ONO radicals undergo two channels predicted by statistical transition-state theory, and an additional non-intrinsic reaction coordinate channel, HNO elimination. CH2CH2ONO is formed with high rotational energy; by employing rotational models based on conservation of angular momentum, we predict, and verify experimentally, the kinetic energies of stable CH2CH2ONO radicals and the angular distribution of dissociation products. The major dissociation pathway of CH2CH2ONO is NO2 + ethene, and some of the NO2 is formed with sufficient internal energy to undergo further photodissociation. Nascent BrCH2CHO and CH2Br are also photodissociated upon absorption of a second 193 nm photon; we derive the kinetic energy release of these dissociations based on our data, noting similarities to the analogous photodissociation of ClCH2CHO and CH2Cl.
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Affiliation(s)
- Preston G Scrape
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States
| | - Trevor D Roberts
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States
| | - Shih-Huang Lee
- National Synchrotron Radiation Research Center , Hsinchu 30076, Taiwan, Republic of China
| | - Laurie J Butler
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States
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Casavecchia P, Leonori F, Balucani N. Reaction dynamics of oxygen atoms with unsaturated hydrocarbons from crossed molecular beam studies: primary products, branching ratios and role of intersystem crossing. INT REV PHYS CHEM 2015. [DOI: 10.1080/0144235x.2015.1039293] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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7
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Booth RS, Brynteson MD, Lee SH, Lin JJ, Butler LJ. Further studies into the photodissociation pathways of 2-bromo-2-nitropropane and the dissociation channels of the 2-nitro-2-propyl radical intermediate. J Phys Chem A 2014; 118:4707-22. [PMID: 24947044 DOI: 10.1021/jp502277v] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
These experiments investigate the decomposition mechanisms of geminal dinitro energetic materials by photolytically generating two key intermediates: 2-nitropropene and 2-nitro-2-propyl radicals. To characterize the unimolecular dissociation of each intermediate, we form them under collision-free conditions using the photodissociation of 2-bromo-2-nitropropane; the intermediates are formed at high internal energies and undergo a multitude of subsequent unimolecular dissociation events investigated herein. Complementing our prior work on this system, the new data obtained with a crossed-laser molecular beam scattering apparatus with VUV photoionization detection at Taiwan's National Synchrotron Radiation Research Center (NSRRC) and new velocity map imaging data better characterize two of the four primary 193 nm photodissociation channels. The C-Br photofission channel forming the 2-nitro-2-propyl radicals has a trimodal recoil kinetic energy distribution, P(ET), suggesting that the 2-nitro-2-propyl radicals are formed both in the ground electronic state and in two low-lying excited electronic states. The new data also revise the HBr photoelimination P(ET) forming the 2-nitropropene intermediate. We then resolved the multiple competing unimolecular dissociation channels of each photoproduct, confirming many of the channels detected in the prior study, but not all. The new data detected HONO product at m/e = 47 using 11.3 eV photoionization from both intermediates; analysis of the momentum-matched products allows us to establish that both 2-nitro-2-propyl → HONO + CH3CCH2 and 2-nitropropene → HONO + C3H4 occur. Photoionization at 9.5 eV allowed us to detect the mass 71 coproduct formed in OH loss from 2-nitro-2-propyl; a channel missed in our prior study. The dynamics of the highly exothermic 2-nitro-2-propyl → NO + acetone dissociation is also better characterized; it evidences a sideways scattered angular distribution. The detection of some stable 2-nitropropene photoproducts allows us to fit signal previously assigned to H loss from 2-nitro-2-propyl radicals. Overall, the data provide a comprehensive study of the unimolecular dissociation channels of these important nitro-containing intermediates.
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Affiliation(s)
- Ryan S Booth
- Department of Chemistry and the James Franck Institute, The University of Chicago , Chicago, Illinois 60637, United States
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Brynteson MD, Womack CC, Booth RS, Lee SH, Lin JJ, Butler LJ. Radical intermediates in the addition of OH to propene: photolytic precursors and angular momentum effects. J Phys Chem A 2014; 118:3211-29. [PMID: 24758210 DOI: 10.1021/jp4108987] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We investigate the photolytic production of two radical intermediates in the reaction of OH with propene, one from addition of the hydroxyl radical to the terminal carbon and the other from addition to the center carbon. In a collision-free environment, we photodissociate a mixture of 1-bromo-2-propanol and 2-bromo-1-propanol at 193 nm to produce these radical intermediates. The data show two primary photolytic processes occur: C-Br photofission and HBr photoelimination. Using a velocity map imaging apparatus, we measured the speed distribution of the recoiling bromine atoms, yielding the distribution of kinetic energies of the nascent C3H6OH radicals + Br. Resolving the velocity distributions of Br((2)P(1/2)) and Br((2)P(3/2)) separately with 2 + 1 REMPI allows us to determine the total (vibrational + rotational) internal energy distribution in the nascent radicals. Using an impulsive model to estimate the rotational energy imparted to the nascent C3H6OH radicals, we predict the percentage of radicals having vibrational energy above and below the lowest dissociation barrier, that to OH + propene; it accurately predicts the measured velocity distribution of the stable C3H6OH radicals. In addition, we use photofragment translational spectroscopy to detect several dissociation products of the unstable C3H6OH radicals: OH + propene, methyl + acetaldehyde, and ethyl + formaldehyde. We also use the angular momenta of the unstable radicals and the tensor of inertia of each to predict the recoil kinetic energy and angular distributions when they dissociate to OH + propene; the prediction gives an excellent fit to the data.
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Affiliation(s)
- M D Brynteson
- Department of Chemistry and the James Franck Institute, The University of Chicago , Chicago, Illinois 60637, United States
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Hobday N, Quinn MS, Nauta K, Andrews DU, Jordan MJT, Kable SH. Experimental and Theoretical Investigation of Triple Fragmentation in the Photodissociation Dynamics of H2CO. J Phys Chem A 2013; 117:12091-103. [DOI: 10.1021/jp404895y] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nicholas Hobday
- School of Chemistry, University of Sydney, Sydney NSW 2006, Australia
| | - Mitch S. Quinn
- School of Chemistry, University of Sydney, Sydney NSW 2006, Australia
| | - Klaas Nauta
- School of Chemistry, University of Sydney, Sydney NSW 2006, Australia
| | - Duncan U. Andrews
- School of Chemistry, University of Sydney, Sydney NSW 2006, Australia
| | | | - Scott H. Kable
- School of Chemistry, University of Sydney, Sydney NSW 2006, Australia
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Balucani N, Skouteris D, Leonori F, Petrucci R, Hamberg M, Geppert WD, Casavecchia P, Rosi M. Combined crossed beam and theoretical studies of the N(2D) + C2H4 reaction and implications for atmospheric models of Titan. J Phys Chem A 2012; 116:10467-79. [PMID: 23016665 DOI: 10.1021/jp3072316] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The dynamics of the H displacement channels in the reaction N((2)D) + C(2)H(4) have been investigated by the crossed molecular beam technique with mass spectrometric detection and time-of-flight analysis at two different collision energies (17.2 and 28.2 kJ/mol). The interpretation of the scattering results is assisted by new electronic structure calculations of stationary points and product energetics for the C(2)H(4)N ground state doublet potential energy surface. RRKM statistical calculations have been performed to derive the product branching ratio under the conditions of the present experiments and of the atmosphere of Titan. Similarities and differences with respect to a recent study performed in crossed beam experiments coupled to ionization via tunable VUV synchrotron radiation are discussed (Lee, S.-H.; et al. Phys. Chem. Chem. Phys.2011, 13, 8515-8525). Implications for the atmospheric chemistry of Titan are presented.
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Affiliation(s)
- Nadia Balucani
- Dipartimento di Chimica, Università degli Studi di Perugia, 06123 Perugia, Italy.
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11
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Womack CC, Ratliff BJ, Butler LJ, Lee SH, Lin JJM. Photoproduct Channels from BrCD2CD2OH at 193 nm and the HDO + Vinyl Products from the CD2CD2OH Radical Intermediate. J Phys Chem A 2012; 116:6394-407. [DOI: 10.1021/jp212167t] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Caroline C. Womack
- The James Franck Institute and
the Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Britni J. Ratliff
- The James Franck Institute and
the Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Laurie J. Butler
- The James Franck Institute and
the Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Shih-Huang Lee
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan, Republic
of China
| | - Jim Jr-Min Lin
- Institute of Atomic
and Molecular
Sciences, Academia Sinica, Taipei 10617,
Taiwan, Republic of China
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Ratliff BJ, Alligood BW, Butler LJ, Lee SH, Lin JJM. Product Branching from the CH2CH2OH Radical Intermediate of the OH + Ethene Reaction. J Phys Chem A 2011; 115:9097-110. [DOI: 10.1021/jp203127k] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Britni J. Ratliff
- The James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Bridget W. Alligood
- The James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Laurie J. Butler
- The James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Shih-Huang Lee
- National Synchrotron Radiation Research Center, Hsinchu, 30076 Taiwan, Republic of China
| | - Jim Jr-Min Lin
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617 Taiwan, Republic of China
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13
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Chin CH, Chaudhuri C, Lee SH. Molecular-beam experiments for photodissociation of propenal at 157 nm and quantum-chemical calculations for migration and elimination of hydrogen atoms in systems C3H4O and C3H3O. J Chem Phys 2011; 135:044301. [DOI: 10.1063/1.3613636] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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14
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Lee SH, Chin CH, Chaudhuri C. Evidence for Synchronous Concerted Three-Body Dissociation of Propenal to C2H2+CO+H2. Chemphyschem 2011; 12:753-6. [DOI: 10.1002/cphc.201001091] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2010] [Indexed: 11/06/2022]
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Chaudhuri C, Lee SH. A complete look at the multi-channel dissociation of propenal photoexcited at 193 nm: branching ratios and distributions of kinetic energy. Phys Chem Chem Phys 2011; 13:7312-21. [DOI: 10.1039/c0cp01641a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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FitzPatrick BL, Alligood BW, Butler LJ, Lee SH, Lin JJM. Primary photodissociation pathways of epichlorohydrin and analysis of the C–C bond fission channels from an O(P3)+allyl radical intermediate. J Chem Phys 2010; 133:094306. [DOI: 10.1063/1.3475001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Lee SH. Dynamics of multi-channel dissociation of tetrahydrofuran photoexcited at 193 nm: distributions of kinetic energy, angular anisotropies and branching ratios. Phys Chem Chem Phys 2010; 12:2655-63. [DOI: 10.1039/b921219a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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18
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Lee SH. The photodissociation of oxetane at 193 nm as the reverse of the Paterno–Buchi reaction. J Chem Phys 2009; 131:224309. [DOI: 10.1063/1.3270162] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Lee SH. Dynamics of multidissociation paths of acetaldehyde photoexcited at 157 nm: Branching ratios, distributions of kinetic energy, and angular anisotropies of products. J Chem Phys 2009; 131:174312. [DOI: 10.1063/1.3262724] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Casavecchia P, Leonori F, Balucani N, Petrucci R, Capozza G, Segoloni E. Probing the dynamics of polyatomic multichannel elementary reactions by crossed molecular beam experiments with soft electron-ionization mass spectrometric detection. Phys Chem Chem Phys 2008; 11:46-65. [PMID: 19081908 DOI: 10.1039/b814709d] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this Perspective we highlight developments in the field of chemical reaction dynamics. Focus is on the advances recently made in the investigation of the dynamics of elementary multichannel radical-molecule and radical-radical reactions, as they have become possible using an improved crossed molecular beam scattering apparatus with universal electron-ionization mass spectrometric detection and time-of-flight analysis. These improvements consist in the implementation of (a) soft ionization detection by tunable low-energy electrons which has permitted us to reduce interfering signals originating from dissociative ionization processes, usually representing a major complication, (b) different beam crossing-angle set-ups which have permitted us to extend the range of collision energies over which a reaction can be studied, from very low (a few kJ mol(-1), as of interest in astrochemistry or planetary atmospheric chemistry) to quite high energies (several tens of kJ mol(-1), as of interest in high temperature combustion systems), and (c) continuous supersonic sources for producing a wide variety of atomic and molecular radical reactant beams. Exploiting these new features it has become possible to tackle the dynamics of a variety of polyatomic multichannel reactions, such as those occurring in many environments ranging from combustion and plasmas to terrestrial/planetary atmospheres and interstellar clouds. By measuring product angular and velocity distributions, after having suppressed or mitigated, when needed, the problem of dissociative ionization of interfering species (reactants, products, background gases) by soft ionization detection, essentially all primary reaction products can be identified, the dynamics of each reaction channel characterized, and the branching ratios determined as a function of collision energy. In general this information, besides being of fundamental relevance, is required for a predictive description of the chemistry of these environments via computer models. Examples are taken from recent on-going work (partly published) on the reactions of atomic oxygen with acetylene, ethylene and allyl radical, of great importance in combustion. A reaction of relevance in interstellar chemistry, as that of atomic carbon with acetylene, is also discussed briefly. Comparison with theoretical results is made wherever possible, both at the level of electronic structure calculations of the potential energy surfaces and dynamical computations. Recent complementary CMB work as well as kinetic work exploiting soft photo-ionization with synchrotron radiation are noted. The examples illustrated in this article demonstrate that the type of dynamical results now obtainable on polyatomic multichannel radical-molecule and radical-radical reactions might well complement reaction kinetics experiments and hence contribute to bridging the gap between microscopic reaction dynamics and thermal reaction kinetics, enhancing significantly our basic knowledge of chemical reactivity and understanding of the elementary reactions which occur in real-world environments.
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Lu IC, Chen WK, Chaudhuri C, Huang WJ, Lin JJ, Lee SH. Exploring the dynamics of reaction N+SiH(4) with crossed molecular-beam experiments and quantum-chemical calculations. J Chem Phys 2008; 129:174304. [PMID: 19045344 DOI: 10.1063/1.3005652] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigated the reaction N((4)S,(2)D,(2)P)+SiH(4) in crossed molecular beams at a collision energy of 4.7 kcal mol(-1) with a time-of-flight mass spectrometer and selective photoionization. Ion signals were observed at m/z=42-45, associated with two product channels, HSiNH/SiNH(2)+H+H and HSiN/HNSi+H(2)+H. The species producing the signal at m/z=43 is assigned to product HSiN/HNSi and that at m/z=44 to product HSiNH/SiNH(2). The signal observed at m/z=42 is attributed to daughter ions of those two products and that at m/z=45 to (29)Si and (30)Si isotopic variants. We report time-of-flight spectra as a function of laboratory angle and simulations for the two products, from which both kinetic-energy and angular distributions of products in the center-of-mass (c.m.) frame were derived. The dependence of release of kinetic energy on the c.m. scattering angle is weak. The average translational energy released is 7.7 kcal mol(-1) for product channel HSiNH/SiNH(2)+H+H and 30.3 kcal mol(-1) for product channel HSiN/HNSi+H(2)+H. Through consecutive triple fragmentation, the angular distribution is slightly anisotropic for product HSiNH/SiNH(2) but isotropic for product HSiN/HNSi. Assuming equal efficiencies of detection, we estimate the branching ratios of products HSiNH/SiNH(2) and HSiN/HNSi to be roughly 15:85. To facilitate an understanding of the reaction mechanisms, we calculated the potential-energy surface for reaction N((2)D)+SiH(4) with quantum-chemical methods. Reactions N((2)D)+SiH(4)-->SiNH(2)+H+H and N((2)D)+SiH(4)-->HNSi+H(2)+H account satisfactorily for the present experimental results. Isomeric products HSiNH and HSiN are minor in this work.
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Affiliation(s)
- I-Chung Lu
- Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
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Fitzpatrick BL, Lau KC, Butler LJ, Lee SH, Lin JJM. Investigation of the O+allyl addition/elimination reaction pathways from the OCH2CHCH2 radical intermediate. J Chem Phys 2008; 129:084301. [PMID: 19044817 DOI: 10.1063/1.2966004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Benjamin L Fitzpatrick
- The James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, USA
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Chen WK, Lu IC, Chaudhuri C, Huang WJ, Lee SH. Investigations of Silicon−Nitrogen Hydrides from Reaction of Nitrogen Atoms with Silane: Experiments and Calculations. J Phys Chem A 2008; 112:8479-86. [DOI: 10.1021/jp804435y] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Wei-Kan Chen
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan
| | - I-Chung Lu
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan
| | - Chanchal Chaudhuri
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan
| | - Wen-Jian Huang
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan
| | - Shih-Huang Lee
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan
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Huang L, Shen Y, Dong W, Zhang R, Zhang J, Hou H. A novel method to decompose two potent greenhouse gases: photoreduction of SF6 and SF5CF3 in the presence of propene. JOURNAL OF HAZARDOUS MATERIALS 2008; 151:323-30. [PMID: 17640803 DOI: 10.1016/j.jhazmat.2007.05.080] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2007] [Revised: 05/23/2007] [Accepted: 05/29/2007] [Indexed: 05/16/2023]
Abstract
SF5CF3 and SF6 are the most effective greenhouse gases on a per molecule basis in the atmosphere. Original laboratory trial for photoreduction of them by use of propene as a reactant was performed to develop a novel technique to destroy them. The highly reductive radicals produced during the photolysis of propene at 184.9 nm, such as .CH3, .C2H3, and .C3H5, could efficiently decompose SF6 and SF5CF3 to CH4, elemental sulfur and trace amounts of fluorinated organic compounds. It was further demonstrated that the destruction and removal efficiency (DRE) of SF5X (X represented F or CF3) was highly dependent on the initial propene-to-SF5X ratio. The addition of certain amounts of oxygen and water vapor not only enhanced the DRE but avoided the generation of deposits. In both systems, employment nitrogen as dilution gas lessened the DRE slightly. Given the advantage of less toxic products, the technique might contribute to SF5X remediation.
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Affiliation(s)
- Li Huang
- Center for Greenhouse Gas Research, Institute of Environmental Science, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, PR China
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Lee SH, Huang WJ, Chen WK. Dynamics of the reaction of atomic oxygen with ethene: Observation of all carbon-containing products by single-photon ionization. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.08.083] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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FitzPatrick BL, Maienschein-Cline M, Butler LJ, Lee SH, Lin JJ. Determining the Partial Photoionization Cross-Sections of Ethyl Radicals. J Phys Chem A 2007; 111:12417-22. [PMID: 17760439 DOI: 10.1021/jp073828h] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Using a crossed laser-molecular beam scattering apparatus, these experiments photodissociate ethyl chloride at 193 nm and detect the Cl and ethyl products, resolved by their center-of-mass recoil velocities, with vacuum ultraviolet photoionization. The data determine the relative partial cross-sections for the photoionization of ethyl radicals to form C2H5+, C2H4+, and C2H3+ at 12.1 and 13.8 eV. The data also determine the internal energy distribution of the ethyl radical prior to photoionization, so we can assess the internal energy dependence of the photoionization cross-sections. The results show that the C2H4++H and C2H3++H2 dissociative photoionization cross-sections strongly depend on the photoionization energy. Calibrating the ethyl radical partial photoionization cross-sections relative to the bandwidth-averaged photoionization cross-section of Cl atoms near 13.8 eV allows us to use these data in conjunction with literature estimates of the Cl atom photoionization cross-sections to put the present bandwidth-averaged cross-sections on an absolute scale. The resulting bandwidth-averaged cross-section for the photoionization of ethyl radicals to C2H5+ near 13.8 eV is 8+/-2 Mb. Comparison of our 12.1 eV data with high-resolution ethyl radical photoionization spectra allows us to roughly put the high-resolution spectrum on the same absolute scale. Thus, one obtains the photoionization cross-section of ethyl radicals to C2H5+ from threshold to 12.1 eV. The data show that the onset of the C2H4++H dissociative photoionization channel is above 12.1 eV; this result offers a simple way to determine whether the signal observed in photoionization experiments on complex mixtures is due to ethyl radicals. We discuss an application of the results for resolving the product branching in the O+allyl bimolecular reaction.
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Affiliation(s)
- B L FitzPatrick
- The James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, USA
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Zhao YL, Laufer AH, Halpern JB, Fahr A. Hydrogen Migration and Vinylidene Pathway for Formation of Methane in the 193 nm Photodissociation of Propene: CH3CHCH2 and CD3CDCD2. J Phys Chem A 2007; 111:8330-5. [PMID: 17685497 DOI: 10.1021/jp072475j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photodissociation channels and the final product yields from the 193 nm photolysis of propene-h6 (CH(2)=CHCH(3)) and propene-d6 (CD(2)=CDCD(3)) have been investigated, employing gas chromatography, mass spectroscopy, and flame ionization (GC/MS/FID) detection methods. The yields of methane as well as butadiene relative to ethane show considerable variations when propene-h6 or propene-d6 are photolyzed. This suggests significant variances in the relative importance of primary photolytic processes and/or secondary radical reactions, occurring subsequent to the photolysis. Theoretical calculations suggest the potential occurrence of an intramolecular dissociation through a mechanism involving vinylidene formation, accompanied by an ethylenic H-migration through the pi-orbitals. This process affects the final yields of methane-h4 versus methane-d4 with respect to other products. The product yields from previous studies of the 193 nm photolysis of methyl vinyl ketone-h6 and -d6 (CH(2)=CHCOCH(3), CD(2)=CDCOCD(3)), alternative precursors for generating methyl and vinyl radicals, are compared with the current results for propene.
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Affiliation(s)
- Yi-Lei Zhao
- Computational Chemistry Group, Physical and Chemical Properties Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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Lu IC, Huang WJ, Chaudhuri C, Chen WK, Lee SH. Development of a stable source of atomic oxygen with a pulsed high-voltage discharge and its application to crossed-beam reactions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2007; 78:083103. [PMID: 17764309 DOI: 10.1063/1.2772090] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
To investigate the reactions of oxygen atoms with ethene and silane in a crossed-beam condition, we developed a stable, highly intense, and short-pulsed source of atomic oxygen with a transient high-voltage discharge. Mixtures of O(2) and He served as discharge media. Utilizing a crossed molecular-beam apparatus and direct vacuum-ultraviolet ionization, we measured the temporal profiles of oxygen atoms and the time-of-flight spectra of reaction products. With O(2) 3% seeded in He as a discharge medium, oxygen atoms might have a full width as small as 13.5 micros at half maximum at a location 193 mm downstream from the discharge region. Most population of oxygen atoms is in the ground state (3)P but some in the first excited state (1)D, depending on the concentration of precursor O(2). This discharge device analogously generates carbon, nitrogen, and fluorine atoms from precursors CO, N(2), and F(2), respectively.
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Affiliation(s)
- I-Chung Lu
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
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Chaudhuri C, Lu IC, Lin JJ, Lee SH. Investigations of oxysilanes from the crossed-beam reaction of atomic oxygen with silane using tunable vacuum-ultraviolet ionization. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.07.048] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Lee SH, Wu CY, Yang SK, Lee YP. Photodissociation dynamics of fluorobenzene (C6H5F) at 157 and 193 nm: Branching ratios and distributions of kinetic energy. J Chem Phys 2006; 125:144301. [PMID: 17042584 DOI: 10.1063/1.2353118] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Following photodissociation of fluorobenzene (C6H5F) at 193 and 157 nm, we detected the products with fragmentation-translational spectroscopy by utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Between two primary dissociation channels observed upon irradiation at 193 (157) nm, the HF-elimination channel C6H5F --> HF + C6H4 dominates, with a branching ratio of 0.94+/-0.02 (0.61+/-0.05) and an average release of kinetic energy of 103 (108) kJ mol(-1); the H-elimination channel C6H5F --> H + C6H4F has a branching ratio of 0.06+/-0.02 (0.39+/-0.05) and an average release of kinetic energy of 18.6 (26.8) kJ mol(-1). Photofragments H, HF, C6H4, and C6H4F produced via the one-photon process have nearly isotropic angular distributions. Both the HF-elimination and the H-elimination channels likely proceed via the ground-state electronic surface following internal conversion of C6H5F; these channels exhibit small fractions of kinetic energy release from the available energy, indicating that the molecular fragments are highly internally excited. We also determined the ionization energy of C6H4F to be 8.6+/-0.2 eV.
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Affiliation(s)
- Shih-Huang Lee
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
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Eves BJ, Lopinski GP. Formation of organic monolayers on silicon via gas-phase photochemical reactions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:3180-5. [PMID: 16548575 DOI: 10.1021/la052960a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
A new method for the formation of molecular monolayers on silicon surfaces utilizing gas-phase photochemical reactions is reported. Hydrogen-terminated Si(111) surfaces were exposed to various gas-phase molecules (hexene, benzaldehyde, and allylamine) and irradiated with ultraviolet light from a mercury lamp. The surfaces were studied with in situ Fourier transform infrared spectroscopy, high-resolution electron energy loss spectroscopy, and scanning tunneling microscopy. The generation of gas-phase radicals was found to be the initiator for organic monolayer formation via the abstraction of hydrogen from the H/Si(111) surface. Monolayer growth can occur through either a radical chain reaction mechanism or through direct radical attachment to the silicon dangling bonds.
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Affiliation(s)
- Brian J Eves
- Steacie Institute for Molecular Sciences, National Research Council, Ottawa, Ontario, Canada
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Lee SH, Ong CS, Lee YT. Evidence of CH2O(ãA23) and C2H4(ãB1u3) produced from photodissociation of 1,3-trimethylene oxide at 193nm. J Chem Phys 2006; 124:74306. [PMID: 16497035 DOI: 10.1063/1.2170084] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We investigated the dissociative ionization of formaldehyde (CH(2)O) and ethene (C(2)H(4)) produced from photolysis of 1,3-trimethylene oxide at 193 nm using a molecular-beam apparatus and vacuum-ultraviolet radiation from an undulator for direct ionization. The CH(2)O (C(2)H(4)) product suffers from severe dissociative ionization to HCO(+) (C(2)H(3) (+) and C(2)H(2) (+)) even though photoionization energy is as small as 9.8 eV. Branching ratios of fragmentation of CH(2)O and C(2)H(4) following ionization are revealed as a function of kinetic energy of products using ionizing photons from 9.8 to 14.8 eV. Except several exceptions, branching ratios of daughter ions increase with increasing photon energy but decrease with increasing kinetic energy. The title reaction produces CH(2)O and C(2)H(4) mostly on electronic ground states but a few likely on triplet states; C(2)H(4) (a(3)B(1u)) seems to have a yield greater than CH(2)O (a(3)A(2)). The distinct features observed at small kinetic energies of daughter ions are attributed to dissociative ionization of photoproducts CH(2)O (a(3)A(2)) and C(2)H(4) (a(3)B(1u)). The observation of triplet products indicates that intersystem crossing occurs prior to fragmentation of 1,3-trimethylene oxide.
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Affiliation(s)
- Shih-Huang Lee
- National Synchrotron Radiation Research Center, Hsinchu Science Park, Taiwan.
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Lee SH, Lee YT. Dependence of the distributions of kinetic energies of products on photoionization energy in the photodissociation of ethene at 157nm. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2005.11.044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Lu IC, Lee SH, Lee YT, Yang X. Photodissociation dynamics of ketene at 157.6nm. J Chem Phys 2006; 124:024324. [PMID: 16422600 DOI: 10.1063/1.2147221] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Photodissociation dynamics of ketene at 157.6 nm has been investigated using the photofragment translational spectroscopic technique based on photoionization detection using vacuum-ultraviolet synchrotron radiation. Three dissociation channels have been observed: CH2+CO, CH+HCO, and HCCO+H. The product translational energy distributions and angular anisotropy parameters were measured for all three observed dissociation channels, and the relative branching ratios for different channels were also estimated. The experimental results show that the direct C-C bond cleavage (CH2+CO) is the dominant channel, while H migration and elimination channels are very minor. The results in this work show that direct dissociation on excited electronic state is much more significant than the indirect dissociation via the ground state in the ketene photodissociation at 157.6 nm.
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Affiliation(s)
- I-Chung Lu
- Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
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Balucani N, Capozza G, Leonori F, Segoloni E, Casavecchia P. Crossed molecular beam reactive scattering: from simple triatomic to multichannel polyatomic reactions. INT REV PHYS CHEM 2006. [DOI: 10.1080/01442350600641305] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Lee SH, Wu CY, Yang SK, Lee YP. Photodissociation dynamics of formyl fluoride (HFCO) at 193 nm: Branching ratios and distributions of kinetic energy. J Chem Phys 2005; 123:074326. [PMID: 16229589 DOI: 10.1063/1.2006093] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Following photodissociation of formyl fluoride (HFCO) at 193 nm, we detected products with fragmentation translational spectroscopy utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Among three primary dissociation channels observed in this work, the F-elimination channel HFCO-->HCO+F dominates, with a branching ratio approximately 0.66 and an average release of kinetic energy approximately 55 kJ mol(-1); about 17% of HCO further decomposes to H+CO. The H-elimination channel HFCO-->FCO+H has a branching ratio approximately 0.28 and an average release of kinetic energy approximately 99 kJ mol(-1); about 21% of FCO further decomposes to F+CO. The F-elimination channel likely proceeds via the S1 surface whereas the H-elimination channel proceeds via the T1 surface; both channels exhibit moderate barriers for dissociation. The molecular HF-elimination channel HFCO-->HF+CO, correlating with the ground electronic surface, has a branching ratio of only approximately 0.06; the average translational release of 93 kJ mol(-1), approximately 15% of available energy, implies that the fragments are highly internally excited. Detailed mechanisms of photodissociation are discussed.
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Affiliation(s)
- Shih-Huang Lee
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
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Lee SH, Lee YT. Angular anisotropy of products in the photodissociation of propene at 157 nm. Chem Phys Lett 2004. [DOI: 10.1016/j.cplett.2004.07.099] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Lee SH, Lee YT, Yang X. Dynamics of photodissociation of ethylene and its isotopomers at 157 nm: Branching ratios and kinetic-energy distributions. J Chem Phys 2004; 120:10983-91. [PMID: 15268128 DOI: 10.1063/1.1740711] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigated the photodissociation of ethylene and its isotopomers at 157 nm in a molecular-beam apparatus using photofragment translational spectroscopy combined with synchrotron-based photoionization. The time-of-flight (TOF) spectra of all photofragments H, H(2), C(2)H(2), C(2)H(3), and their deuterium isotopic variants were recorded, from which kinetic-energy distributions P(E(t)) and branching ratios were obtained. Most C(2)H(3) spontaneously dissociates to C(2)H(2)+H and only C(2)H(3) with small internal energy survives. The C(2)H(2) fragment due to H(2) elimination is observed leading the C(2)H(2) fragment due to 2H elimination in TOF distribution because the former process has more kinetic-energy release. An analogous result is observed for C(2)D(4) photolysis. That elimination of molecular hydrogen is site-specific and is revealed from photolysis of three dideuterated ethylene isotopomers, in which an isotopic effect plays a significant role. Observations of C(2)D(2)+2H and C(2)H(2)+2D product channels in the photolysis of 1,1-CH(2)CD(2) provide evidence for migrations of H and D atoms. A comparison with previous experimental and theoretical results is made.
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Affiliation(s)
- Shih-Huang Lee
- National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30077, Taiwan, Republic of China.
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Lee SH, Lee YT, Yang X. Dynamics of photodissociation of 3,3,3-d3-propene at 157 nm: Site effect and hydrogen migration. J Chem Phys 2004; 120:10992-9. [PMID: 15268129 DOI: 10.1063/1.1747812] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In a preceding paper [Lee et al., J. Chem. Phys. 119, 827 (2003)], we measured the kinetic-energy distributions P(E(t)) and branching ratios of products from photolysis of propene at 157 nm using time-of-flight spectroscopy combined with photoionization. In the present work, hydrogen migration before fragmentation and a site effect on P(E(t)) and branching ratios were revealed from the photodissociation of CD(3)CHCH(2). Labeling of the methyl group with deuterium enabled us to differentiate between elimination of atomic and molecular hydrogen from the vinyl moiety and from the methyl moiety; the P(E(t)) and relative yields for the formation of H, D, H(2), HD, and D(2) were measured. Deuterium labeling allowed us to also differentiate the fragmentation after hydrogen transfer from that before hydrogen migration. The observation of isotopic variants of CD(3) and C(2)H(3) radicals in the C-C bond cleavage provides evidence for hydrogen transfer of propene because of site specificity. The fraction of fragmentation after hydrogen transfer is estimated to be 25%. The isotope-specific branching ratios for five dissociation pathways of CD(3)CHCH(2) were evaluated.
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Affiliation(s)
- Shih-Huang Lee
- National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Science Park, Hsinchu 30077, Taiwan, Republic of China.
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Capozza G, Segoloni E, Leonori F, Volpi GG, Casavecchia P. Soft electron impact ionization in crossed molecular beam reactive scattering: The dynamics of the O(3P)+C2H2 reaction. J Chem Phys 2004; 120:4557-60. [PMID: 15267314 DOI: 10.1063/1.1652013] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Soft ionization by low-energy, tunable electrons is implemented for the first time in crossed molecular beam reactive scattering experiments with mass-spectrometric detection. The power of the method, which permits the suppression of the dissociative ionization of interfering species, is exemplified with the study of the O((3)P)+C(2)H(2) multichannel reaction.
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Affiliation(s)
- Giovanni Capozza
- Dipartimento di Chimica, Universita di Perugia, 06100 Perugia, Italy
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Lee SH, Lee HI, Lee YT. Distributions of angular anisotropy and kinetic energy of products from the photodissociation of methanol at 157 nm. J Chem Phys 2004; 121:11053-9. [PMID: 15634056 DOI: 10.1063/1.1814099] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigated distributions of angular-anisotropy parameter beta and kinetic energy of fragments after photodissociation of methanol using time-of-flight (TOF) mass spectrometry. Fragments, in particular CH(3)O and CO, were successfully detected using tunable radiation from a synchrotron for photoionization. Following O-H bond fission, a CH(3)O fragment with internal energy greater than 104 kJ mol(-1) dissociates to CH(2)O+H. Elimination of two H(2) accompanies formation of CO. The beta value of hydroxyl hydrogen is -0.26 whereas that of methyl hydrogen is zero. H(2) has two distinct components in TOF spectra; these rapid and slow components have beta values -0.30 and -0.18, respectively. The CH(3)+OH dissociation exhibits a highly anisotropic angular distribution with beta= -0.75. The beta values of fragments from CD(3)OH photolysis are addressed. From measurements of angular-anisotropy parameters of various fragments, we surmise that the transition dipole moment mu is almost perpendicular to the C-O-H plane and that n-3p(x) (2 (1)A") is the major photoexcited state at 157 nm.
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Affiliation(s)
- Shih-Huang Lee
- National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30077, Taiwan.
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