Absolute rate constants for the gas-phase reaction of the nitrate radical with dimethyl sulfide, nitrogen dioxide, carbon monoxide and a series of alkanes at 298 .+-. 2 K

Abstract

A flash photolysis-visible absorption apparatus has been constructed and employed in a study of the kinetics of the gas-phase reactions of the NO/sub 3/ radical with CH/sub 3/SCH/sub 3/, NO/sub 2/, CO, CH/sub 4/, C/sub 2/H/sub 6/, and n-C/sub 4/H/sub 10/. The measured absolute rate constants at 298 +/- 2 K are as follows (in units of 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/): CH/sub 3/SCH/sub 3/, 7.5 +/- 0.5 independent of pressure over the range 50-400 Torr; NO/sub 2/, 5.6 +/- 0.4 and 8.0 +/- 1.1 at 120 and 400 Torr total pressure of helium, respectively; CO, less than or equal to 0.00003; CH/sub 4/, less than or equal to 0.0002; C/sub 2/H/sub 6/, less than or equal to 0.00004; n-C/sub 4/H/sub 10/, less than or equal to 0.0002. The error limits represent two standard deviations. (Systematic errors could contribute an additional approx. 10% range.) These results are discussed with respect to the previous literature data and the atmospheric lifetimes of these compounds. The rate constant for the reaction of NO/sub 3/ radicals with CH/sub 3/SCH/sub 3/ measured in the present work is consistent with both another recent absolute determination and previous relative rate measurements, confirming the relativemore » rate technique previously used to determine NO/sub 3/ radical reaction rate constants.« less