ULTRAVIOLET-ABSORPTION SPECTRA AND KINETICS OF THE SELF-REACTION OF CH2BR AND CH2BRO2 RADICALS IN THE GAS-PHASE AT 298-K

The ultraviolet absorption spectra of CH2Br and CH2BrO2 radicals and the kinetics of their self-reactions have been studied in the gas phase at 298 K by using the pulse radiolysis technique. Absorption cross sections were quantified over the wavelength range 220-350 nm. Measured cross sections near the absorption maxima were sigma(CH2Br)(280 nm) = (6.26 +/- 1.15) x 10(-18) cm2 molecule-1 and sigma(CH2BrO2)(250 nm) = (7.20 +/- 0.83) x 10(-18) cm2 molecule-1. Errors represent statistical errors (2-sigma) together with our estimate of potential systematic errors (10%). The absorption cross-sectional data were then used to derive the observed self-reaction rate constants for reactions 1 and 2, defined as -d[R]/dt = 2k(obs)[R]2 (R = CH2Br or CH2BrO2) of CH2Br + CH2Br --> products (1) CH2BrO2 + CH2BrO2 --> products (2) k1 = (2.93 +/- 0.60) x 10(-11) cm3 molecule-1 s-1 and k2obs = (3.26 +/- 0.31) x 10(-11) cm3 molecule-1 s-1 (quoted errors represent 2-sigma). These results are discussed with respect to previous studies of the absorption spectra and kinetics of peroxy radicals.