E. Roth

Study of a benzoylperoxy radical in the gas phase: ultraviolet spectrum and C6H5C(O)O2 + HO2 reaction between 295 and 357 K.

This work reports the ultraviolet absorption spectrum and the kinetic determinations of the reactions 2C(6)H(5)C(O)O(2) → products (I) and C(6)H(5)C(O)O(2) + HO(2) → C(6)H(5)C(O)O(2)H + O(2) (IIa), → C(6)H(5)C(O)OH + O(3) (IIb), → C(6)H(5)C(O)O + OH + O(2) (IIc). Experiments were performed using a laser photolysis technique coupled with UV-visible absorption detection over the pressure range of 80-120 Torr and the temperature range of 293-357 K. The UV spectrum was determined relative to the known cross section of the ethylperoxy radical C(2)H(5)O(2) at 250 nm. Kinetic data were obtained by simulating the temporal behavior of the UV absorption at 245-260 nm. At room temperature, the rate constant value of reaction I (cm(3)·molecule(-1)·s(-1)) was found to be k(I) = (1.5 ± 0.6) × 10(-11). The Arrhenius expression for reaction II is (cm(3)·molecule(-1)·s(-1)) k(II)(T) = (1.10 ± 0.20) × 10(-11) exp(364 ± 200/T). The branching ratios β(O3) and β(OH), respectively, of reactions IIb and IIc are evaluated at different temperatures; β(O3) increases from 0.15 ± 0.05 at room temperature to 0.40 ± 0.05 at 357 K, whereas β(OH) remains constant at 0.20 ± 0.05. To confirm the mechanism of reaction II, a theoretical study was performed at the B3LYP/6-311++G(2d,pd) level of theory followed by CBS-QB3 energy calculations.