The ethylperoxy radical: its ultraviolet spectrum, self-reaction, and reaction with hydroperoxy, each studied as a function of temperature

Abstract

The ultraviolet spectrum of the ethylperoxy radical (C2H502) and the reactions C2H5O2 + C2H5O2 -products (1) and C2H5O2 + H02 -C2H502H + 0 2 ( 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 umax = (4.89 f 0.60) X lo-'* cm2 molecule-' at 240 nm. The temperature dependence of the broadness of the spectrum as well as the value of umax 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 kl/cm3 molecule-' s-I = (6.7 f 0.6) X exp((60 f 40)/TJ 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 ks/cm3 molecule-' s-I = (1.6 f 0.4) X lO-I3 expi( 1260 f 130)/ 7') 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-' s-I = (1.10 f 0.21) X lo-". This result holds implications for the understanding of the reactivity of R02 species with H02, which is important for the chemical modeling of the troposphere.

UV absorption spectra of HO2, CH3O2, C2H5O2, and CH3C(O)CH2O2 radicals and mechanism of the reactions of F and Cl atoms with CH3C(O)CH3

“…As shown in Fig. 4C, the ethyl peroxy radical spectrum measured herein is in excellent agreement with those of Wallington et al 25, Maricq and Wallington 24, Bauer et al 26, Fenter et al 27, and the recommendation of Tyndall et al 4, but is significantly different from that reported by Munk et al 28. The present study was performed in the same laboratory using essentially the same apparatus as employed by Munk et al 28 and the difference in results deserves comment.…”

Unraveling the structure and chemical mechanisms of highly oxygenated intermediates in oxidation of organic compounds

“…At 500–600 K, peroxy radical isomerization reactions compete with bimolecular reactions (e.g., cross-combination and recombination of RO 2 ) and formation of dimer compounds ( 1 , 18 ). For example, the rate constant of RO 2 + RO 2 (e.g., C 2 H 5 O 2 + C 2 H 5 O 2 ) is on the order of 10 10 cm 3 ⋅mol −1 ⋅s −1 at 298 K and has a weak negative temperature dependence ( 31 ), while the intramolecular H-atom abstraction of the RO 2 radical via a six-membered-ring transition state is on the order of 10 −3 s −1 at 298 K ( 23 ). However, the intramolecular H-atom abstraction is strongly temperature dependent and its rate is on the order of 10 4 s −1 at 550 K ( 32 ).…”

An experimental and computational study of the methyl formate radical ultraviolet spectrum

“…12,14,15 The concentration of the methyl formate radical present at the measured delay time following laser photolysis is dependent on the initial reactions ͑2͒ and ͑3͒ as well as the following secondary reactions: The initial atomic chlorine, or fluorine, concentration is determined by calibration against ethylperoxy radical; Ϸ2-3 Torr ethane and Ϸ25 Torr O 2 are substituted for methyl formate plus a portion of the N 2 buffer, while maintaining the same amount of Cl 2 or F 2 as in the corresponding methyl formate radical measurement, and the C 2 H 5 O 2 concentration is measured via its previously reported UV cross section.…”