Temperature-Dependent Kinetics Studies of the Reactions Br(2P3/2) + CH3SCH3 CH3SCH2 + HBr. Heat of Formation of the CH3SCH2 Radical

Article abstract of DOI:10.1021/j100080a006

Time-resolved resonance fluorescence detection of Br(²P_3/2) atom disappearence or appearance following 266-nm laser flash photolysis CF2Br2/CH3SCH3/H2/N2 and Cl2CO/CH3SCH3/HBr/H2/N2 mixtures has been employed to study the kinetics of the reactions Br((2)P_3/2) + CH3SCH3 <*> HBr + CH3SCH2 (1,-1) as a function of temperature over the range 386 604 K.Arrhenius expressions in units of cm³ molecule^-1 s^-1 which describe the results are k₁ = (9.0 +/- 2.9) x 1E-11 > and k_-1 = (8.6 +/- 2.5) x 1E-13 >; errors are 2? and represent precision only.To our knowledge, these are the first kinetic data reported for each of the two reactions studied.Second and third law analyses of the equilibrium data for reactions 1 and -1 have been employed to obtain the following enthalpies of reaction in units of kcal mol^-1; ΔH₂₉₈ = 6.11 +/- 1.37 and ΔH₀ = 5.37 +/- 1.38.Combining the above enthalpies of reaction with the well-known heats of formation of Br, HBr, and CH3SCH3 gives the following heats of formation of the CH3SCH2 radical in units of kcal mol^-1: ΔH_f,298 = 32.7 +/- 1.4 and ΔH_f,0 = 35.3 +/- 1.4; errors are 2? and represent estimates of absolute accuracy.The C-H bond dissociation energy in CH3SCH3 obtained from our data, 93.7 +/- 1.4 kcal mol^-1 at 298 K and 92.0 +/- 1.4 kcal mol^-1 at 0 K, agrees well with a recent molecular beam photofragmentation study but is 3 kcal mol^-1 lower than the value obtained from an iodination kinetics study.