Ab initio study of the isomerization and photodissociation of the C 3H 6O + [rad] cation radicals

Abstract

We have performed ab initio (using Gaussian-2 (G2M) method) calculations for the reactant, intermediates, transition states, and photofragmentation products of the C 3H 6O + cation radicals in order to elucidate its unimolecular photofragmentation and isomerization mechanisms. We have identified nine photofragmentation pathways, 39 stable intermediates, and 61 transition states for the acetone cation radical C H 3 COC H 3 + as an initial state by ab initio calculations. The isomerization pathways among them are also characterized. It was found that the photofragmentation and isomerization pathways are intertwined through various transition states. Two of the nine pathways contain only one transition state with high energy (70–80 kcal/mol) just after the reactant. In the other ones, the reactant acetone cation radical is transformed into an enol structure via one transition state, and enol and ether isomers undergo many-step isomerizations. From the ab initio calculation, the reaction pathways found in this work have energy barriers higher than those obtained by Heinrich et al. [J. Am. Chem. Soc. 110 (1988) 8183]. In general, the photofragmentation species not investigated previously are found to have high energies, which coincides with the fact that the previous experiments conducted with low laser intensity and short wavelength do not reveal such species.