Theoretical Study of the Low-Lying Excited States of Butoxy Radicals and Non-Radiative Decay Routes

The potential energy surfaces for the butoxy radical dissociation into R·+O on the six low-lying electronic states have been determined with the combined CASSCF and MR-CI methods. The isomerization reactions between the different conformers of 1- and 2-butoxy radicals at the X̃ and B̃ states have been also investigated with the MP2, B3LYP, and CASSCF methods. The non-radiative decay mechanisms of butoxy radicals at the B̃ state have been characterized with the computed potential energy surfaces and intersections. Supported by recent LIF experimental results, it was predicted that the t-butoxy radical would predissociate via the B̃/ C̃ intersection. As to 1- and 2-butoxy radicals, the relative energies of the transition states for the isomerization reactions between conformers at the B̃ state are much lower than those of the B̃/C̃ intersections, resulting in the predominance of the isomerization in the decay of the B̃ state for 1- and 2-butoxy radicals.