Ab Initio Study of the Photochemical Dissociation of Methylamine

Abstract

The threshold photochemistry of methylamine along three dissociation channels is examined using CASSCF and MRSDCI wave functions. Excitation of a nitrogen lone pair electron into a Rydberg s orbital produces an excited state that can decompose via NH rupture, CN rupture, or CH rupture. In the case of NH and CN rupture the excited state and ground state surfaces cross as the molecule dissociates, forming a conical intersection. The NH rupture excited state products lie above the excitation energy, and so dissociating molecules are funneled through the conical intersection and emerge as ground state products. The CN rupture excited state products lie below the excitation energy, and dissociation would proceed mostly on the excited state surface. In the case of CH rupture, the excited state products lie above the excitation energy, but since there is no conical intersection in this channel, CH rupture has to occur only after internal conversion to the ground state. These three mechanisms are all consistent w...