Kinetics of the multichannel reaction of methanethiyl radical (CH 3S ̇) with 3O 2

Document Type

Article

Publication Date

6-1-2006

Abstract

The CH 3S ̇ + O 2 reaction system is considered an important process in atmospheric chemistry and in combustion as a pathway for the exothermic conversion of methane-thiyl radical, CH 3S ̇. Several density functional and ab initio computational methods are used in this study to determine thermochemical parameters, reaction paths, and kinetic barriers in the CH 3S ̇ + O 2 reaction system. The data are also used to evaluate feasibility of the DFT methods for higher molecular weight oxy-sulfur hydrocarbons, where sulfur presents added complexity from its many valence states. The methods include: B3LYP/6-311++G(d,p), B3LYP/6-311++G(3df,2p), CCSD(T)/6-311G(d,p)//MP2/6-31G(d,p), B3P86/6-311G(2d,2p)//B3P86/6-31G(d), B3PW91/ 6-311++G(3df,2p), G3MP2, and CBS-QB3. The well depth for the CH 3S ̇ + 3O 2 reaction to the syn-CH 3SOO ̇ adduct is found to be 9.7 kcal/mol. Low barrier exit channels from the syn-CH 3SOO ̇ adduct include: CH 2S + HO 2, (TS6, E a is 12.5 kcal/mol), CH 3 + SO 2 via CH 3SO 2 (TS2′, E a is 17.8) and CH 3SO + O (TS17, E a is 24.7) where the activation energy is relative to the syn-CH 3SOO ̇ stabilized adduct. The transition state (TS5) for formation of the CH 3SOO adduct from CH 3S ̇ + O 2 and the reverse dissociation of CH 3SOO to CH 3S ̇ + O 2 is relatively tight compared to typical association and simple bond dissociation reactions; this is a result of the very weak interaction. Reverse reaction is the dominant dissociation path due to enthalpy and entropy considerations. The rate constants from the chemical activation reaction and from the stabilized adduct to these products are estimated as functions of temperature and pressure. Our forward rate constant and CH 3S loss profile are in agreement with the experiments under similar conditions. Of the methods above, the G3MP2 and CBS-QB3 composite methods are recommended for thermochemical determinations on these carbon-sulfur-oxygen systems, when they are feasible. © 2006 American Chemical Society.

Identifier

33745439714 (Scopus)

Publication Title

Journal of Physical Chemistry A

External Full Text Location

https://doi.org/10.1021/jp056209m

ISSN

10895639

First Page

6923

Last Page

6937

Issue

21

Volume

110

This document is currently not available here.

Share

COinS