Ab initio kinetics for decomposition/isomerization reactions of C2H5O radicals.

Radical reactions: The ground-state potential energy surface of the C(2)H(5)O system is investigated by ab initio methods using optimized geometries. The rate constants for the unimolecular isomerization and decomposition reactions of the three isomeric radicals (see picture) are calculated by microcanonical transition-state theory at 200-3000 K, varying the pressures of the diluents.The ground-state potential energy surface of the C(2)H(5)O system, including the decomposition and isomerization of the ethoxy (CH(3)CH(2)O), 1-hydroxyethyl (CH(3)CHOH), and 2-hydroxyethyl (CH(2)CH(2)OH) radicals, is computed by the modified Gaussian-2 (G2M) and CCSD(T)/6-311+G(3df,2p) methods by using the geometries optimized at the B3LYP/6-311+G(3df,2p) level of theory. These detailed reaction pathways are used to calculate the rate constants for the unimolecular isomerization and decomposition reactions of the three radicals by the microcanonical transition-state theory and Rice-Ramsperger-Kassel-Marcus (RRKM) theory in the temperature range of 200-3000 K at varying pressures of He and other diluents. The predicted rate constants are in reasonable agreement with the available experimental data. In addition, the predicted heats of formation of the three isomeric radicals are compared with available experimental and theoretical values.