Aspects of the reaction mechanism of ethane combustion. Conformations of the ethylperoxy radical

The detailed molecular understanding of hydrocarbon combustion processes is recognized as an important goal. The specific system studied-via ab initio theoretical methods - in this work is the reaction between the ethyl radical (C{sub 2}H{sub 5}{degrees}) and molecular oxygen (O{sub 2}). It may be argued that further experimental work on this system will yield limited new insights until theoretical investigations of the potential energy surface are made. Theoretical methods used include self-consistent-field (SCF) and configuration interaction including all single and double excitations (CISD) with up to double zeta plus polarization (DZP) quality basis sets. A total of 55 distinct stationary points on the C{sub 2}H{sub 5}(O82){degrees} potential energy surface were considered here. Two excited states of the ethylperoxy radical, six conformers of the ground {sup 2}A inch state, and four conformers of the excited {sup 2}A (foot), state were studied. For the ground-state surface, the barrier between the staggered and gauche structures is only 1.0 kcal mol{sup {minus}1}. The barrier to internal rotation of the methyl group is between 2.5 and 3.0 kcal mol{sup {minus}1} depending on the level of theory. 74 refs., 3 figs., 7 tabs.