Ab Initio Calculations of the Potential Energy Surfaces for the Unimolecular Dissociation Reaction of Ethylene Oxide

Ab initio calculations, including electron correlation, were employed to compute the geometries and energies of all stable C2H4O species, as well as four transition states along the potential surfaces connecting oxirane to the unimolecular dissociation products. The calculations indicate that the primary step in the major reaction observed experimentally is the isomerization of oxirane along the ground-state potential surface to acetaldehyde. Calculations indicate that the experimental reaction products are derived from unimolecular decomposition on the acetaldehyde S0 surface (CH4+CO) or, after intersystem crossing, along the lowest triplet state of acetaldehyde (CH3+HCO). Additional pathways connecting oxirane to a number of less energetically favorable ring-opened or fragmentation products are also presented.