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

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 (Kobc) 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.