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Author(s):   Zhu, L.; Bozzelli, J.W.
Title:   Kinetics of the multichannel reaction of methanethiyl radical (CH3S center dot) with O-3(2)
Journal:   J. Phys. Chem. A
Volume:   110
Page(s):   6923 - 6937
Year:   2006
Reference type:   Journal article
Squib:   2006ZHU/BOZ6923-6937

Reaction:   CH3 + O2·CH3 + SO2
Reaction order:   2
Temperature:   200 - 2000 K
Pressure:  0.10 bar
Rate expression:   6.23x10-8 [cm3/molecule s] (T/298 K)-3.80 e-51463 [J/mole]/RT
Category:  Theory
Data type:   Ab initio
Pressure dependence:   Rate constant is pressure dependent
Comments:   Several dozen different reaction channels for the atmospheric chemistry relevant CH3S + O2 were explored using DFT and ab initio methods. Predominantly the energetics in the paper were reported based on G3MP2 and CBS-QB3 calculations. Most of the reaction channels and intermediates were unimportant under wide range of pressure and temperature conditions. Only the dominant primary and secondary channels were abstracted here. Rate expressions were provided for a range of low to high pressures. Only 0.1 atm rate expressions were abstracted here. Reported rate expressions were based on TST or QRRK/Master Equation analysis. Total calculated rate of reaction is slightly different than experimental value. Authors attribute this to a calculated CH3SOO well depth that is too low.

CH3S + O2
-> CH3SOO
-> CH2S + HO2
->CH3SO + O
->CH3+SO2

CH3SOO adduct is is formed (9 kcal/mol downhill), and can revert back to reactants, or go on to react to form directly CH2S+ HO2 (13 kcal barrier) or CH3SO + O (25 kcal barrier). It can also isomerize to CH3S(O)(O) (18 kcal barrier) which then quicikly dissociates to CH3 + SO2.

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Rate constant values calculated from the Arrhenius expression:

T (K)k(T) [cm3/molecule s]
200 1.03E-20
300 6.66E-17
400 3.88E-15
500 3.67E-14
600 1.44E-13
700 3.51E-13
800 6.38E-13
900 9.63E-13
1000 1.28E-12
1100 1.57E-12
1200 1.80E-12
1300 1.98E-12
1400 2.10E-12
1500 2.16E-12
1600 2.19E-12
1700 2.19E-12
1800 2.15E-12
1900 2.10E-12
2000 2.04E-12