Ultraviolet absorption spectra and kinetics of the self-reaction of bromomethyl and peroxybromomethyl radicals in the gas phase at 298 K

Abstract

The ultraviolet absorption spectra of CH{sub 2}Br and CH{sub 2}BrO{sub 2} 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}{sub CH{sub 2}Br}(280 nm) = (6.26 {plus minus} 1.15) {times} 10{sup {minus}18} cm{sup 2} molecule{sup {minus} 1}. Errors represent statistical errors (2{sigma}) together with the authors' 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 {minus}d(R)/dt = 2k{sub obs}(R){sup 2} (R = CH{sub 2}Br or CH{sub 2}BrO{sub 2}) of CH{sub 2}Br + CH{sub 2}BR {yields} products (1), and CH{sub 2}BrO{sub 2} + CH{sub 2}BrO{sub 2} {yields} products (2) k{sub 1} = (2.93 {plus minus} 0.60) {times} 10{sup {minus}11} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} and k{sub 2obs} = (3.26 {plus minus} 0.31) {times} 10{sup {minus}11} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} (quoted errors represent 2{sigma}). These results are discussed with respect to previous studies of the absorption spectra and kinetics of peroxy radicals.