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Theoretical study for the reaction of CH 3 OCl with Cl atom
Author(s) -
He HongQing,
Liu JingYao,
Li ZeSheng,
Sun ChiaChung
Publication year - 2005
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.20202
Subject(s) - isodesmic reaction , chemistry , reaction rate constant , ab initio , potential energy surface , transition state theory , atmospheric temperature range , thermodynamics , atom (system on chip) , kinetics , standard enthalpy of formation , physics , quantum mechanics , organic chemistry , embedded system , computer science
A direct dynamics method is employed to study the kinetics of the multiple channel reaction CH 3 OCl + Cl. The potential energy surface (PES) information is explored from ab initio calculations. Two reaction channels, Cl‐ and H‐abstractions, have been identified. The optimized geometries and frequencies of the stationary points and the minimum‐energy paths (MEPs) are calculated at the MP2 level of theory using the 6‐311G( d , p ) and cc‐pVTZ basis sets, respectively. The single‐point energies along the MEPs are further refined at the G3(MP2)//MP2/6‐311G( d , p ), G3//MP2/6‐311G( d , p ), as well as by the multicoefficient correlation method based on QCISD (MC‐QCISD) using the MP2/cc‐pVTZ geometries. The enthalpies of formation for the species CH 3 OCl and CH 2 OCl are calculated via isodesmic reactions. The rate constants of the two reaction channels are evaluated by using the variational transition‐state theory over a wide range of temperature, 220–2200 K. The calculated rate constants exhibit the slightly negative temperature dependence and show good agreement with the available experimental data at room temperature at the G3(MP2)//MP2/6‐311G( d , p ) level. The present calculations indicate that the two channels are competitive at low temperatures while H‐abstraction plays a more important role with the increase of temperature. The calculated k 1a / k 1 ratio of 0.5 at 298 K is in general agreement with the experimental one, 0.8 ± 0.2. The high rate constant for CH 3 OCl + Cl shows that removal by reaction with Cl atom is a potentially important loss process for CH 3 OCl in the polar stratosphere. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 642–650, 2005