2-Bromoethylperoxy and 2-bromo-1-methylpropylperoxy radicals: ultraviolet absorption spectra and self-reaction rate constants at 298 K

Abstract

The self-reaction rate constants and UV absorption spectra of two brominated peroxy radicals, BrCH₂CH₂O₂(2-bromoethylperoxy) and (CH₃)BrCHCH(CH₃)O₂(2-bromo-1-methylpropylperoxy) have been measured using the molecular modulation technique, Self-reaction rate constants (K_obc) of (6.2 ± 1.2)× 10^–12 and (9.6 ± 1.9)× 10^–13 cm³ molecule^–1 s^–1 were obtained for BrCH₂CH₂O₂ and (CH₃)BrCHCH(CH₃)O₂, respectively. In both cases secondary chemistry is likely to enhance the removal rate of the radicals and the given rate constants are expected to be slightly higher than the true value. The UV spectra of both radicals are broad absorptions with maxima close to 240 nm. Absolute cross-sections at 270 nm were found to be (2.2 ± 0.4)× 10^–18 and (2.8 ± 0.6)× 10^–18 cm² molecule^–1 for BrCH₂CH₂O₂ and (CH₃)BrCHCH(CH₃)O₂, respectively. The measured values of self-reaction rate constants and UV absorption spectra are compared to results for C₂H₅O₂. In addition, a long-lived transient absorption was observed in the BrCH₂O₂CH₂O₂ experiments, and is thought to be due to BrCH₂CH₂OOBr, a product of an association reaction between Br atoms and BrCH₂CH₂O₂.