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Title: Thermodynamic properties of bromomethanes and bromomethyl radicals: An ab initio study

Abstract

Thermochemical data on volatile organic compounds containing bromine are needed for atmospheric modeling, in view of their ozone depletion potential upon photodissociation and the release of atomic bromine. Yet even for the bromomethane series, with the exception of CH{sub 3}Br, thermodynamic properties are not well established. Similarly, structural and thermochemical information on brominated methyl radicals is incomplete or not available. In this paper the authors have adopted a computational approach to obtain this needed information. Equilibrium geometries for the molecules CH{sub 4{minus}n}Br{sub n} (n = 0--4) and radicals CH{sub 3{minus}m}Br{sub m} (m = 0--3) were optimized at both HF/6-31G{sup *} and MP2/6-31G{sup *} levels of theory. Moments of inertia, harmonic vibrational frequencies, and thermodynamic functions were determined at the HF/6-31G{sup *} level. Electron correlation contributions were performed by single-point calculations at both second- and fourth-order Moeller-Plesset perturbation theory for derived MP2/6-31G{sup *} geometries. Enthalpies of formation were obtained from a consideration of applicable isodesmic reactions using the derived MP4/6-31G{sup **}//MP2/6-31G{sup *} total energies in conjunction with experimentally established enthalpies of formation for CH{sub 3}Br, CH{sub 4}, and CH{sub 3}. These data were then used in the determination of {Delta}H{degree}{sub f,T}, {Delta}G{degree}{sub f,T}, and K{sub f,T} for all species over themore » temperature range 0 to 1500 K. A comparison was made to the existing standard enthalpies of formation at 298 K, both experimentally measured and theoretically estimated, for CH{sub 2}Br{sub 2}, CHBr{sub 3}, CBr{sub 4}, CH{sub 2}Br{sm_bullet}, CHBr{sub 2}{sm_bullet}, and CBr{sub 3}{sm_bullet}.« less

Authors:
;  [1]
  1. Univ. of Calgary, Alberta (Canada). Dept. of Chemistry
Publication Date:
OSTI Identifier:
675543
Report Number(s):
CONF-970629-
Journal ID: IJTHDY; ISSN 0195-928X; TRN: IM9833%%152
Resource Type:
Journal Article
Journal Name:
International Journal of Thermophysics
Additional Journal Information:
Journal Volume: 19; Journal Issue: 3; Conference: 13. symposium on thermophysical properties, Boulder, CO (United States), 22-27 Jun 1997; Other Information: PBD: May 1998
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; AIR POLLUTION; ATMOSPHERIC CHEMISTRY; THERMODYNAMIC PROPERTIES; VOLATILE MATTER; BROMINATED ALIPHATIC HYDROCARBONS

Citation Formats

Paddison, S J, and Tschuikow-Roux, E. Thermodynamic properties of bromomethanes and bromomethyl radicals: An ab initio study. United States: N. p., 1998. Web. doi:10.1023/A:1022670318235.
Paddison, S J, & Tschuikow-Roux, E. Thermodynamic properties of bromomethanes and bromomethyl radicals: An ab initio study. United States. https://doi.org/10.1023/A:1022670318235
Paddison, S J, and Tschuikow-Roux, E. 1998. "Thermodynamic properties of bromomethanes and bromomethyl radicals: An ab initio study". United States. https://doi.org/10.1023/A:1022670318235.
@article{osti_675543,
title = {Thermodynamic properties of bromomethanes and bromomethyl radicals: An ab initio study},
author = {Paddison, S J and Tschuikow-Roux, E},
abstractNote = {Thermochemical data on volatile organic compounds containing bromine are needed for atmospheric modeling, in view of their ozone depletion potential upon photodissociation and the release of atomic bromine. Yet even for the bromomethane series, with the exception of CH{sub 3}Br, thermodynamic properties are not well established. Similarly, structural and thermochemical information on brominated methyl radicals is incomplete or not available. In this paper the authors have adopted a computational approach to obtain this needed information. Equilibrium geometries for the molecules CH{sub 4{minus}n}Br{sub n} (n = 0--4) and radicals CH{sub 3{minus}m}Br{sub m} (m = 0--3) were optimized at both HF/6-31G{sup *} and MP2/6-31G{sup *} levels of theory. Moments of inertia, harmonic vibrational frequencies, and thermodynamic functions were determined at the HF/6-31G{sup *} level. Electron correlation contributions were performed by single-point calculations at both second- and fourth-order Moeller-Plesset perturbation theory for derived MP2/6-31G{sup *} geometries. Enthalpies of formation were obtained from a consideration of applicable isodesmic reactions using the derived MP4/6-31G{sup **}//MP2/6-31G{sup *} total energies in conjunction with experimentally established enthalpies of formation for CH{sub 3}Br, CH{sub 4}, and CH{sub 3}. These data were then used in the determination of {Delta}H{degree}{sub f,T}, {Delta}G{degree}{sub f,T}, and K{sub f,T} for all species over the temperature range 0 to 1500 K. A comparison was made to the existing standard enthalpies of formation at 298 K, both experimentally measured and theoretically estimated, for CH{sub 2}Br{sub 2}, CHBr{sub 3}, CBr{sub 4}, CH{sub 2}Br{sm_bullet}, CHBr{sub 2}{sm_bullet}, and CBr{sub 3}{sm_bullet}.},
doi = {10.1023/A:1022670318235},
url = {https://www.osti.gov/biblio/675543}, journal = {International Journal of Thermophysics},
number = 3,
volume = 19,
place = {United States},
year = {Fri May 01 00:00:00 EDT 1998},
month = {Fri May 01 00:00:00 EDT 1998}
}