Abstract
Nonempirical molecular orbital calculations have been carried out on the So (ground), Si, Tj, and T2 states of azomethane and on selected states of diimide and azoethane. Potential energy surfaces for several possible isomerization pathways
from trans to cis isomers have been obtained. Motions in which one alkyl group rotates about the N=N bond or moves in the
N=N—R plane through a linear configuration appear to be of considerable importance, while the motion which simultaneously linearizes both N=N—R groups is forbidden by a substantial energy barrier. Spectral and thermodynamic quantities
calculated are in good agreement with the experimental data where available. The shapes of the energy surfaces provide explanations for such phenomena as the lack of observed fluorescence and phosphorescence in acyclic azoalkanes and the variation
in the quantum yields of isomerization and dissociation with pressure and with the method of excitation.