Geometries and Energies of Nitrobenzene Studied by CAS-SCF Calculations

Abstract

Optimized geometries and energies in the ground (S0) and excited states of nitrobenzene were calculated using the CAS-SCF method. The optimized geometries in the S1, S2, T1, T2, and T3 states are very different from that in the S0 state. Most significantly, the nitro group is largely bent out of the phenyl plane in the excited states. The potential curves along the nitro rotation coordinate around the C−N bond and the out-of-plane bending mode of the nitro group in the S0, S1, T1, and T2 states were calculated in relation to the excited states dynamics. It is found that the potential curves along the bending mode in the excited states are very flat compared with that in the S0 state. The mechanisms for the fast relaxation from the S1 and T1 states are discussed based on the ab initio results.