Theoretical calculations of the excited state potential energy surfaces of nitric oxide

Excited state potential energy surfaces of NO are studied using density functional theory and coupled cluster theory exploiting a recently developed algorithm called the maximum overlap method. States arising from excitation to Rydberg orbitals are described well, with coupled cluster theory providing properties comparable in accuracy to multi-reference configuration interaction calculations. For the π → π∗ valence states, larger errors are observed with density functional theory, and coupled cluster theory fails. This is associated with the multiconfigurational nature of these states. The calculations yield pseudo diabatic states, allowing the surface crossing between the B2Π and C2Π states to be studied directly.