The Ethylperoxy Radical: Its Ultraviolet Spectrum, Self-Reaction, and Reaction with HO2, Each Studied as a Function of Temperature

Article abstract of DOI:10.1021/j100116a016

The ultraviolet spectrum of the ethylperoxy radical (C2H5O2) and the reactions C2H5O2 + C2H5O2 --> products (1) and C2H5O2 + HO2 --> C2H5O2H + O2 (5) have been studied using the flash photolysis/UV absorption technique.The spectrum was taken between the wavelengths of 210 and 290 nm and at the temperatures of 298 and 600 K.The room temperature spectrum is found to be in good agreement with previous determinations, with a maximum cross section ?_max = (4.89 +/- 0.60) * 10^-18 cm² molecule^-1 at 240 nm.The temperature dependence of the broadness of the spectrum as well as the value of ?_max is analyzed by fitting the data to a Gaussian function that predicts the temperature behavior of broad, structureless UV absorptions.Our results on the C2H5O2 self-reaction are also in good agreement with previous studies, with k₁/cm³ molecule^-1 s^-1 = (6.7 +/- 0.6) * 10^-14 exp<(60 +/- 40)/T> for the temperature range 248-460 K.At higher temperatures, we observe non-second-order kinetic behavior which can be attributed to the thermal decomposition of the ethoxy radical, a product of reaction 1.Our results for the reaction C2H5O2 + HO2 are significantly different from the only previous determination of its temperature dependence, especially at and below room temperature, with k₅/cm³ molecule^-1 s^-1 = (1.6 +/- 0.4) * 10^-13 exp<(1260 +/- 130)/T> over the temperature range of 248-480 K; our room temperature rate constant is about a factor of 2 greater than the currently accepted value of k₅, with k₅(298)/cm³ molecule^-1 s^-1 * 10^-11.This result holds implications for the understanding of the reactivity of RO2 species with HO2, which is important for the chemical modeling of the troposphere.