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Charfeddine F, Zanchet A, Yazidi O, Cuevas CA, Saiz-Lopez A, Bañares L, García-Vela A. Photodissociation of the CH2Br radical: A theoretical study. J Chem Phys 2024; 160:074301. [PMID: 38364009 DOI: 10.1063/5.0187546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 12/21/2023] [Indexed: 02/18/2024] Open
Abstract
Bromine atom (Br) reactions lead to ozone depletion in the troposphere and stratosphere. Photodegradation of bromocarbons is one of the main sources of bromine atoms in the atmosphere. Here, we use high-level ab initio methods, including spin-orbit effects, to study the photodissociation of the CH2Br radical. All possible fragmentation pathways, namely CH2Br + hν → CH2 + Br, HCBr + H, and CBr + H2, have been analyzed. Potential-energy curves of the ground and several excited electronic states along the corresponding dissociating bond distance of each pathway have been calculated. Considering the actinic fluxes of solar irradiation in the troposphere and in the stratosphere in the relevant range of frequencies, it is found that the first five excited states of CH2Br can be accessed from the ground state. Analysis of the potential curves shows that the pathways producing CH2 + Br and HCBr + H can proceed through a fast direct dissociation mechanism, while the pathway leading to CBr + H2 involves much slower dissociation mechanisms like internal conversion between electronic states, predissociation, or tunneling through exit barriers. The main implications are that the two faster channels are predicted to be dominant, and the slower pathway is expected to be less relevant. The tropospheric and stratospheric solar actinic fluxes also allow for further dissociation of the HCBr and CBr fragments, generating additional Br atoms, provided that they survive possible collisions with other atmospheric reagents. Finally, we discuss the possible effect of each of the three CH2Br dissociation pathways on the depletion of atmospheric ozone.
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Affiliation(s)
- F Charfeddine
- Laboratoire de Spectroscopie Atomique, Moleculaire et Applications-LSAMA LR01ES09, Faculte des Sciences de Tunis, Universite de Tunis El Manar, 2092 Tunis, Tunisia
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, Serrano 123, 28006 Madrid, Spain
| | - A Zanchet
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, Serrano 123, 28006 Madrid, Spain
| | - O Yazidi
- Laboratoire de Spectroscopie Atomique, Moleculaire et Applications-LSAMA LR01ES09, Faculte des Sciences de Tunis, Universite de Tunis El Manar, 2092 Tunis, Tunisia
| | - C A Cuevas
- Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Blas Cabrera, CSIC, 28006 Madrid, Spain
| | - A Saiz-Lopez
- Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Blas Cabrera, CSIC, 28006 Madrid, Spain
| | - L Bañares
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid (Unidad Asociada I+D+i CSIC), 28040 Madrid, Spain
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanoscience), 28049 Madrid, Spain
| | - A García-Vela
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, Serrano 123, 28006 Madrid, Spain
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Haakansson CT, Corkish TR, Watson PD, McKinley AJ, Wild DA. The bromide-bromomethyl radical dimer complex: Anion photoelectron spectroscopy and CCSD(T) calculations. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2020.138060] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Kortyna A, Doney K, Nesbitt DJ. High-resolution infrared spectroscopy of jet cooled CH 2Br radicals: The symmetric CH stretch manifold and absence of nuclear spin cooling. J Chem Phys 2020; 152:134305. [DOI: 10.1063/5.0002165] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Andrew Kortyna
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, USA
| | - Kirstin Doney
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, USA
| | - D. J. Nesbitt
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, USA
- Department of Chemistry, University of Colorado, Boulder, Colorado 80309, USA
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
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Kortyna A, Lesko DMB, Nesbitt DJ. High-resolution sub-Doppler infrared spectroscopy of atmospherically relevant Criegee precursor CH 2I radicals: CH 2 stretch vibrations and "charge-sloshing" dynamics. J Chem Phys 2018; 148:174308. [PMID: 29739209 DOI: 10.1063/1.5028287] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The combination of a pulsed supersonic slit-discharge source and single-mode difference frequency direct absorption infrared spectroscopy permit first high resolution infrared study of the iodomethyl (CH2I) radical, with the CH2I radical species generated in a slit jet Ne/He discharge and cooled to 16 K in the supersonic expansion. Dual laser beam detection and collisional collimation in the slit expansion yield sub-Doppler linewidths (60 MHz), an absolute frequency calibration of 13 MHz, and absorbance sensitivities within a factor of two of the shot-noise limit. Fully rovibrationally resolved direct absorption spectra of the CH2 symmetric stretch mode (ν2) are obtained and fitted to a Watson asymmetric top Hamiltonian with electron spin-rotation coupling, providing precision rotational constants and spin-rotation tensor elements for the vibrationally excited state. Analysis of the asymmetric top rotational constants confirms a vibrationally averaged planar geometry in both the ground- and first-excited vibrational levels. Sub-Doppler resolution permits additional nuclear spin hyperfine structures to be observed, with splittings in excellent agreement with microwave measurements on the ground state. Spectroscopic data on CH2I facilitate systematic comparison with previous studies of halogen-substituted methyl radicals, with the periodic trends strongly correlated with the electronegativity of the halogen atom. Interestingly, we do not observe any asymmetric CH2 stretch transitions, despite S/N ≈ 25:1 on strongest lines in the corresponding symmetric CH2 stretch manifold. This dramatic reversal of the more typical 3:1 antisymmetric/symmetric CH2 stretch intensity ratio signals a vibrational transition moment poorly described by simple "bond-dipole" models. Instead, the data suggest that this anomalous intensity ratio arises from "charge sloshing" dynamics in the highly polar carbon-iodine bond, as supported by ab initio electron differential density plots and indeed consistent with observations in other halomethyl radicals and protonated cluster ions.
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Affiliation(s)
- A Kortyna
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, USA
| | - D M B Lesko
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA
| | - D J Nesbitt
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, USA
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Bailleux S, Kania P, Skřínský J, Okabayashi T, Tanimoto M, Matsumoto S, Ozeki H. Hyperfine Resolved Fourier Transform Microwave and Millimeter-Wave Spectroscopy of the Iodomethyl Radical, CH2I (X̃2B1). J Phys Chem A 2010; 114:4776-84. [DOI: 10.1021/jp909323h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | | | | | | | | | | | - Hiroyuki Ozeki
- Department of Environmental Science, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi 274-8510, Japan
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