Publications

Reactions of α-hydroxyethyl (CH3CHOH) and β-hydroxyethyl (CH2CH2OH) radicals with oxygen are of key importance in ethanol combustion. High-level ab initio calculations of the potential energy surfaces of these two reactions were coupled with master equation methods to compute rate coefficients and product branching ratios for temperatures of 250-1000 K. The α-hydroxyethyl + O2 reaction is controlled by the barrierless entrance channel and shows negligible pressure dependence; in contrast, the reaction of the β isomer displays pronounced pressure dependence. The high pressure limit rate coefficients of both reactions are about the same at the temperatures investigated. Products of the reactions were monitored experimentally at 4 Torr and 300-600 K using tunable synchrotron photoionization mass spectrometry. Hydroxyethyl radicals were produced from the reaction of ethanol with chlorine atoms and the β isomer was also selectively produced by the addition reaction C2H4 + OH → CH2CH2OH. Formaldehyde, acetaldehyde, vinyl alcohol and H2O2 products were detected, in qualitative agreement with the theoretical predictions. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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The production of OH and HO2 in Cl-initiated oxidation of cyclohexane has been measured using pulsed-laser photolytic initiation and continuous-laser absorption detection. The experimental data are modeled by master equation calculations that employ new G2(MP2)-like ab initio characterizations of important stationary points on the cyclo-C 6H11O2 surface. These ab initio calculations are a substantial expansion on previously published characterizations, including explicit consideration of conformational changes (chair-boat, axial-equatorial) and torsional potentials. The rate constants for the decomposition and ring-opening of cyclohexyl radical are also computed with ab initio based transition state theory calculations. Comparison of kinetic simulations based on the master equation results with the present experimental data and with literature determinations of branching fractions suggests adjustment of several transition state energies below their ab initio values. Simulations with the adjusted values agree well with the body of experimental data. The results once again emphasize the importance of both direct and indirect components of the kinetics for the production of both HO2 and OH in radical + O 2 reactions. © the Owner Societies.

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