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Godara S, Paranjothy M. Competing Molecular and Radical Pathways in the Dissociation of Halons via Direct Chemical Dynamics Simulations. J Phys Chem A 2019; 123:8527-8535. [PMID: 31539256 DOI: 10.1021/acs.jpca.9b06564] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
A great deal of attention has been given to the decomposition chemistry of halons (halomethanes) due to their role in stratospheric ozone depletion. Knowledge of certain aspects of dissociation of halons such as the competition between radical and molecular pathways and their mechanistic details is limited. Halon molecules can isomerize to an iso form containing a halogen-halogen bond and such iso-halon forms have been identified as intermediates in condensed phase chemistry. Recently, a quantum chemistry study of role of iso-halons in the gas phase decomposition of halomethanes has been reported. In the present work, we have investigated the ground state dissociation chemistry of select halon molecules - CF2Cl2, CF2Br2, CHBr3, and CH2BrCl using electronic structure theory calculations and direct chemical dynamics simulations. Classical trajectories were generated on-the-fly using density functional PBE0/6-31G* level of theory at a fixed total energy. Simulation results showed that molecular products, in general, were dominant for all the four molecules at the chosen energy. A variety of mechanisms such as direct dissociation via multicenter transition states, decomposition via isomerization, radical recombinations, and roaming pathways contributed to the formation of molecular products. Atomic level mechanisms are presented, and the role of iso-halons in the gas phase chemistry of halomethanes is clearly established.
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Affiliation(s)
- Sumitra Godara
- Department of Chemistry , Indian Institute of Technology Jodhpur , Jodhpur , 342037 Rajasthan , India
| | - Manikandan Paranjothy
- Department of Chemistry , Indian Institute of Technology Jodhpur , Jodhpur , 342037 Rajasthan , India
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Chen W, Zhou X, Han Y. Theoretical and experimental studies on the atmospheric degradation of 2-bromo-3,3,3-trifluoropropene. Phys Chem Chem Phys 2015. [PMID: 26197997 DOI: 10.1039/c5cp01457c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
As a new kind of Halon replacement, 2-bromo-3,3,3-trifluoropropene (2-BTP) is finding application as a fire extinguishing agent in confined spaces. For assessing its environmental impact, it is necessary to perform kinetic and product studies of its degradation in the atmospheric environment. In this sense, five possible reaction pathways between 2-BTP and OH radicals are found by Gaussian 03. Detailed analysis shows that the main product is the CF3CBrCH2OH radical, which may produce a series of compounds by further reaction with O2, NO, etc. In order to further prove the validity of the theoretical calculations and investigate the atmospheric transformation process of 2-BTP, atmospheric degradation of 2-BTP is then studied experimentally under controlled radiation conditions. Based on the theoretical analyses and experimental results, the atmospheric degradation mechanism of 2-BTP is finally proposed and detailed information on the atmospheric chemistry of 2-BTP is provided.
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Affiliation(s)
- Weiwang Chen
- The College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China.
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Cho HG, Andrews L. Matrix Infrared Spectra and Density Functional Calculations of CH2Cl-Cl and CH2Br-Br Produced by Laser-ablated Metal Plume Irradiation. B KOREAN CHEM SOC 2015. [DOI: 10.1002/bkcs.10301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Han-Gook Cho
- Department of Chemistry; Incheon National University; Incheon 406-772 Korea
| | - Lester Andrews
- Department of Chemistry; University of Virginia; Charlottesville VA 22904-4319 USA
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Kalume A, George L, Powell AD, Dawes R, Reid SA. Photoinduced electron transfer in donor-acceptor complexes of ethylene with molecular and atomic iodine. J Phys Chem A 2014; 118:6838-45. [PMID: 25075444 DOI: 10.1021/jp412212h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Building upon our recent studies of radical addition pathways following excitation of the I2 chromophore in the donor-acceptor complex of ethylene and I2 (C2H4···I2), in this article, we extend our studies to examine photoinduced electron transfer. Thus, irradiation into the intense charge-transfer band of the complex (λmax = 247 nm) gave rise to a band at 366 nm that is assigned to the bridged ethylene-I radical complex on the basis of our prior work. The formation of the radical complex is explained by a mechanism that involves rapid back electron transfer leading to I-I bond fission. Excitation into the charge-transfer band of the radical complex led to regeneration of the parent complex and the formation of the final photoproduct, anti- and gauche-1,2-diiodoethane, which confirms that the reaction proceeds ultimately by a radical addition mechanism. This finding is contrasted with our previous study of the C2H4···Br2 complex, where CT excitation led to only one product, anti-1,2-dibromoethane, a result explained by a single electron-transfer mechanism proceeding via a bridged bromonium ion intermediate. For the I2 complex, the breakup of the photolytically generated I2(-•) anion radical is apparently sufficiently slow to render it uncompetitive with back electron transfer. Finally, we report a detailed computational examination of the parent and radical complexes of both bromine and iodine, using high-level single- and multireference methods, which provide insight into the different behaviors of the charge-transfer states of the two radicals and the role of spin-orbit coupling.
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Affiliation(s)
- Aimable Kalume
- Department of Chemistry, Marquette University , Milwaukee, Wisconsin 53233, United States
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Reid SA. When isomerisation is electron transfer: the intriguing story of the iso-halocarbons. INT REV PHYS CHEM 2014. [DOI: 10.1080/0144235x.2014.942548] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Anderson CP, Spears KG, Wilson KR, Sension RJ. Solvent dependent branching between C-I and C-Br bond cleavage following 266 nm excitation of CH2BrI. J Chem Phys 2014; 139:194307. [PMID: 24320326 DOI: 10.1063/1.4829899] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
It is well known that ultraviolet photoexcitation of halomethanes results in halogen-carbon bond cleavage. Each halogen-carbon bond has a dominant ultraviolet (UV) absorption that promotes an electron from a nonbonding halogen orbital (nX) to a carbon-halogen antibonding orbital (σ*C-X). UV absorption into specific transitions in the gas phase results primarily in selective cleavage of the corresponding carbon-halogen bond. In the present work, broadband ultrafast UV-visible transient absorption studies of CH2BrI reveal a more complex photochemistry in solution. Transient absorption spectra are reported spanning the range from 275 nm to 750 nm and 300 fs to 3 ns following excitation of CH2BrI at 266 nm in acetonitrile, 2-butanol, and cyclohexane. Channels involving formation of CH2Br + I radical pairs, iso-CH2Br-I, and iso-CH2I-Br are identified. The solvent environment has a significant influence on the branching ratios, and on the formation and stability of iso-CH2Br-I. Both iso-CH2Br-I and iso-CH2I-Br are observed in cyclohexane with a ratio of ~2.8:1. In acetonitrile this ratio is 7:1 or larger. The observation of formation of iso-CH2I-Br photoproduct as well as iso-CH2Br-I following 266 nm excitation is a novel result that suggests complexity in the dissociation mechanism. We also report a solvent and concentration dependent lifetime of iso-CH2Br-I. At low concentrations the lifetime is >4 ns in acetonitrile, 1.9 ns in 2-butanol and ~1.4 ns in cyclohexane. These lifetimes decrease with higher initial concentrations of CH2BrI. The concentration dependence highlights the role that intermolecular interactions can play in the quenching of unstable isomers of dihalomethanes.
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Affiliation(s)
- Christopher P Anderson
- Department of Chemistry and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
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Kalume A, George L, Cunningham N, Reid SA. Case of the Missing Isomer: Pathways for Molecular Elimination in the Photoinduced Decomposition of 1,1-Dibromoethane. J Phys Chem A 2013; 117:11915-23. [DOI: 10.1021/jp403114s] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Aimable Kalume
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881,
United States
| | - Lisa George
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881,
United States
| | - Nicole Cunningham
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881,
United States
| | - Scott A. Reid
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881,
United States
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Kalume A, George L, Cunningham N, Reid SA. Concerted and sequential pathways of proton-coupled electron transfer in hydrogen halide elimination. Chem Phys Lett 2013. [DOI: 10.1016/j.cplett.2012.11.053] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Probing radical pathways in electrophilic addition of halogens: Classical vs. bridged intermediates. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.10.034] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Kalume A, George L, Reid SA. On the electronic spectroscopy of the iso-polyhalomethanes. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.08.066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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George L, Kalume A, Reid SA, Esselman BJ, McMahon RJ. Spectroscopic and computational studies of matrix-isolated iso-CXBr3 (X=F, Cl, Br): Structure, properties, and photochemistry of substituted iso-tribromomethanes. J Mol Struct 2012. [DOI: 10.1016/j.molstruc.2011.12.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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George L, Kalume A, Esselman BJ, Wagner J, McMahon RJ, Reid SA. Spectroscopic and computational studies of matrix-isolated iso-CHBr3: Structure, properties, and photochemistry of iso-bromoform. J Chem Phys 2011; 135:124503. [PMID: 21974531 DOI: 10.1063/1.3640887] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Lisa George
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53233, USA
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Preston TJ, Dutta M, Esselman BJ, Kalume A, George L, McMahon RJ, Reid SA, Fleming Crim F. Formation and relaxation dynamics of iso-CH2Cl–I in cryogenic matrices. J Chem Phys 2011; 135:114503. [DOI: 10.1063/1.3633697] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Femtosecond photolysis of CH2Br2 in acetonitrile: Capturing the bromomethyl radical and bromine-atom charge transfer complex through deep-to-near UV probing. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.02.046] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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El-Khoury PZ, George L, Kalume A, Schapiro I, Olivucci M, Tarnovsky AN, Reid SA. Matrix isolation and computational studies of the CF2I radical. Chem Phys Lett 2010. [DOI: 10.1016/j.cplett.2010.07.032] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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