MECHANISTIC AND KINETIC-STUDY OF FORMALDEHYDE PRODUCTION IN THE ATMOSPHERIC OXIDATION OF DIMETHYL SULFIDE

Tunable diode laser spectroscopic detection of formaldehyde (H2CO) and HCl coupled with laser flash photolysis of Cl2CO-CH3SCH3-O-2-N-2 mixt ures, in both the presence and absence of NO, has been utilized to con duct a mechanistic and kinetic investigation of the atmospheric oxidat ion of the CH3SCH2 radical, a product of dimethyl sulfide (DMS, CH3SCH 3) reactions with OH and NO3 in the atmosphere. The temperature depend ence of the CH3SCH2O2 + NO rate coefficient (k(2)) and the 298 K rate coefficient for the CH3SCH2O2 self reaction (k(4)) have been measured. The Arrhenius expression k(2) = 4.9 x 10(-12) exp(263/T) cm(3) molecu le(-1)s(-1) adequately summarizes our CH3SCH2O2 + NO kinetic data over the temperature range 261400 K. Contributions from side reactions, wh ich are not completely quantifiable, limit the accuracy of the k(4) (2 98 K) determination; our results indicate that the true value for this rate coefficient is within the range (1.2 + 0.5) x 10(-11) cm(3) mole cule(-1)s(-1). In both reactions CH3SCH2O2 is converted to H2CO with u nit yield (at T = 298 K). Our results demonstrate that the lifetime of CH3SCH2O2 a proposed precursor to H2CO, is less than 30 mu s at 261 K and 10 Torr total pressure.