Kinetic study of the self-reactions of the BrCH2CH2O2 and BrCH(CH3)CH(CH3)O2 radicals between 275 and 373 K

A conventional flash photolysis technique was used to measure the self-reaction rate constants of the primary BrCH 2 CH 2 O 2 (2-bromoethylperoxy) and secondary BrCH(CH 3 )CH(CH 3 )O 2 (2-bromo- 1 -methylpropylperoxy) β-brominated peroxy radicals, at temperatures in the range of 275 -373 K. The absolute UV absorption spectra of BrCH 2 CH 2 O 2 and BrCH(CH 3 )CH(CH 3 )O 2 were also measured and compared to those obtained previously for these radicals. The temperature dependence of the self-reaction rate constants provided the following Arrhenius expressions: k(BrCH 2 CH 2 O 2 + BrCH 2 CH 2 O 2 ) = (6.15 + 5 . 5 1 - 2 . 9 1 ) x 10 - 1 4 exp{(1247 ′ 203) K/T} cm 3 molecule - 1 s - 1 and k(BrCH(CH 3 )CH(CH 3 )O 2 + BrCH(CH3)CH(CH3)O 2 ) = (7.60 + 2 2 . 0 5 - 5 . 6 5 ) x 10 - 1 5 exp{(1305 ′ 428) K/T} cm 3 molecule - 1 s - 1 , where the uncertainties represent 95% confidence limits associated with the statistical fitting procedure and include the contribution for the expanded uncertainties in the individual rate constant. These results confirm the enhancement of the peroxy radical self-reaction reactivity upon β-substitution, which is similar for Br, Cl, or OH substituents. Structure-activity relationships are proposed for self-reactions of β-substituted peroxy radicals.