Spectrokinetic Studies of Ethyl and Ethylperoxy Radicals

Article abstract of DOI:10.1021/j100403a038

Hydrogen atoms were produced by pulse radiolysis of H2 at 1 atm and T = 298 K.The yield of H atoms was determined by monitoring the UV absorption of HO2 produced in the presence of oxygen via the reaction H + O2(+M) -> HO2 (+M).In the presence of small amounts of C2H4 we observed the formation of ethyl radicals via H + C2H4 (+M) -> C2H5 (+M) (6) as well as the subsequent decay via 2C2H5 -> C4H10, C2H4 + C2H6 (8).The spectrum of C2H5 is composed of two absorption bands with maxima at 205 and 245 nm.The 205-nm band exhibits a characteristic fine structure with a maximum extinction coefficient of 2010 +/- 300 M^-1 cn^-1.The weaker 245-nm band appears to be a broad continuum with an extinction coefficient of 870 +/- 130 M^-1 cm^-1.By computer-aided analysis of the kinetic features we have obtained values of k₆ = (5.5 +/- 0.5)*E8 M^-1 s^-1 and 2k₈ = (2.3 +/- 0.3)*E10 M^-1 s^-1.In the presence of both C2H4 and O2 we observed the formation of ethylperoxy radicals, C2H5 + O2 (+M) -> C2H5O2 (+M) (10a), followed by a slow second-order decay, 2C2H5O2 -> products (13).The spectrum of C2H5O2 is a broad continuum with a maximum at 230 nm and ε = 1410 +/- 200 M^-1 cm^-1.From the observed rate of formation we obtained k_10a = (3.2 +/- 0.1)*E9 M^-1 s^-1 at p(M) = p(H2) = 1 atm.From the observed second-order decay we have determined 2k₁₃ = (6.3 +/- 0.3)*E7 M^-1 s^-1.The rate of reaction 10a was studied in the range of 298-400 K, and the results may be presented in terms of an Arrhenius expression with an apparent negative activation energy, log k_10a/M^-1 s^-1 = (8.90 +/- 0.04) + (840 +/- 70) cal mol^-1/2.303 RT.