KINETIC AND MECHANISTIC STUDY OF THE REACTION OF ATOMIC CHLORINE WITH DIMETHYL SULFIDE

Time-resolved resonance fluorescence detection of Cl(P-2(J)) following 266-nm laser flash photolysis of Cl2CO/CH3SCH3(DMS)/N2 mixtures has been employed to study the kinetics of the title reaction over the temperature and pressure ranges 240-421 K and 3-700 Torr. The reaction is found to be very fast, occurring on essentially every Cl(P-2(J)) + DMS encounter. The reaction rate increases with decreasing temperature and shows a significant pressure dependence. At 297 K, for example, the rate coefficient increases from a low-pressure limit value of approximately 1.8 X 10(-10) cm3 molecule-1 s-1 to a value of (3.3 +/- 0.5) X 10(-10) cm3 molecule-1 s-1 at P = 700 Torr. A few experiments were carried out with CD3SCD3 or C2H5SC2H5 replacing DMS as the sulfide reactant; within experimental uncertainty, no dependence of the rate coefficient on the identity of the sulfide reactant was observed. In a separate study, time-resolved tunable diode laser spectroscopic detection of HCl has been coupled with 248-nm laser flash photolysis of Cl2CO/DMS/CO2/N2 mixtures to measure the HCI product yield from the title reaction as a function of pressure at T = 297 K. The HCl yield approaches unity as P --> 0 but with increasing pressure to a value of approximately 0.5 at P = 203 Torr. The yield experiments demonstrate that hydrogen abstraction is the dominant reaction mechanism in the low-pressure limit. With increasing pressure, stabilization of a (CH3)2SCl adduct apparently becomes competitive with the hydrogen abstraction pathway. The fate of the stabilized adduct remains highly uncertain, although it clearly does not dissociate to Cl(P-2(J)) or HCl on the time scale of our experiments (several milliseconds). The potential role of the title reaction in marine atmospheric chemistry is discussed.