NOVEL METHOD FOR THE MEASUREMENT OF GAS-PHASE PEROXY RADICAL ABSORPTION-SPECTRA

The pulse radiolysis method has been used to generate methyl peroxy radicals in the presence of high concentrations of NO. The CH3O2 radicals are then rapidly converted to CH3ONO by reaction with NO. Methyl nitrite absorbs strongly in the UV. Hence the initial absorption attributable to CH3O2 is rapidly replaced by absorption by CH3ONO. By varying the monitoring wavelength one can readily determine the isosbestic point, where sigma(CH3O2) = sigma(CH3ONO) + sigma(NO2). For methyl peroxy radicals the isosbestic point was determined to lie in the wavelength range 228-230 nm, and hence sigma(CH3O2) = (3.9 +/- 0.4) x 10(-18) cm2 molecule-1. Quoted errors are the sum of statistical (2-sigma) and our estimate of potential systematic errors (5%). As part of the present work rate constants for reactions 11 and 14 at 298 K and 600 mbar total pressure of SF6 were determined to be CH3 + NO + M --> CH3NO + M (11) F + O2 + M --> FO2 + M (14) k11 = (1.07 +/- 0.03) x 10(-11) cm3 molecule-1 s-1 and k14 = (2.35 +/- 0.20) x 10(-13) cm3 molecule-1 s-1 at 298 K. Results are discussed with respect to previous literature data.