The kinetics of the gas phase pyrolysis of dimethyl sulfide (DMS) was studied in a static system a t 681-723 K by monitoring total pressure-time behavior. Analysis showed the pressure increase to follow DMS loss. The reaction follows two concurrent paths: Me2SC2H4 + H2S --% CH, + CHzS with a slow, minor, secondary reaction:In a seasoned reactor the reaction follows a 3/2 order rate law with rate coefficient given by log[k(L"2/mo11'2 s)] = 13.84 _f 0.21 -(51.4 2 0.7)/0 with 0 = 2.303 R T in kcal/mol. A free radical mechanism is proposed to account for the data and a theoretical rate coefficient is derived from independent data: log[k(L'2/mo11'2 s)] = 12.8 t 0.3 -(47 5 1.5)/0 which agrees well with the experimental one over the range studied. The reaction is initiated by Me$ + Me + MeS and propagated by metathetical radical attack on Me$. C2H, is formed by a n isornerization reaction which may in part be due to a hot radical:Thermochemical data are listed, many from estimations, for both molecular and radical species of interest in the present system.

Experimental rate data for some radical-radical and some atom-molecule reactions are quantitatively accounted for by a proposed model in which the preferred reaction path, with high rate constants, is recombination followed by stabilization or a chemically activated concerted decomposition. When the energetics prohibits such pathways, the metathesis with lower reaction cross sections remains the significant one. The selected pathways and log k (L/mol s) values which were obtained for Cl + H02 and HC1 + 0 are presented. H02 + Cl HC1 + 02(1)stratosphere by trapping Cl as HC1.1 Several experi-ments1-5,9 have been conducted to measure its kinetic parameters. The reported values found for log ¿x (298) of 10.3 ± 0.4,210.2 ± 0.2,910.6 ± 0.1,310.4 ± 0.2,4 5and 10.6 ± 0.21 L/(mol s) seem to be higher than even the effective collision frequency (log Z ( = 1.7 Á) = 10.2 L/(mol s)).

The currently reported values of the heat of formation of hydroperoxyl radical have been reviewed. A best value, Mff°(H02) = 3.5^5°kcal/mol, is recommended.

The gas-phase reaction CH3SH + IZ has been studied spectrophotometrically over the temperature range of 476-604 K. It was found that the reaction undergoes H abstraction by I at 5575 K, leading to the formation of MeSI and followed by a secondary reaction which leads to the formation of MeSSMe:Taking into consideration the effect of reaction (2), the equilibrium constant Kl(554 K) has been evaluated to be 0.025 f 0.004. This value was combined with the estimated values Sg8 (CHBSI, g) = 73.7 f 1.0 eu and (AC0,1,554) = 0.87 f 0.3 eu to obtain AH~,zss = 4.03 f 0.73 kcal/mol. This yields AHym (CH3S1, g) = 7.16 f 0.73 kcal/mol when combined with known thermochemical values for CHBH, HI, and 12. A kinetic study was vitiated by the concurrent heterogeneous reaction of MeSH and 12 at lower temperatures and the rather complicated chemistry occurring at elevated temperatures. However, attempts at measuring rate constants at 554 K lead to a lower limit of (CHsS., g) t 29.5 f 2 kcaVmol when an estimated value of A = 1010.8*0.z L/mol.s for the reaction I t CH3SH S? CH3S t HI is used. D H L (CH3S-I) is estimated to be 49.3 f 1.7 kcal/mol. The bond strengths of some divalent sulfurs and the reaction mechanisms are discussed. A crude estimate of DHO(H-CH2SH) = 96 f 1 kcal has been obtained from the kinetic data.