Ab initio study of valence state potential energy curves of N₂

Abstract

Valence state calculations are reported for the nitrogen molecule, including the X1Σg+ ground state and A3Σu+, B3Πg, W3Δu, B′3Σu-, a′1Σu-, a1Πg, w1Δu, C3Πu, b1Πu, and b′1Σu+ states, whose dominant configurations are single orbital excitations from the ground state, and G3Δg, H3Φu, A′5Σg+ and C″5Πu states, which are predominantly double excitations from the ground state. Configuration interaction (CI) wave functions expanded in a CSF space of all valence configurations plus first- and second-order configurations, which use single and double orbital substitutions into the dominant configuration of each state, are shown to well describe these states around Re. Exceptions are C3Πu, b1Πu, and b′1Σu+, which need more elaborate treatments that include multiple "dominant" configurations, rydbergization of orbitals, and mixing with Rydberg states. Spectroscopic analyses of the potential curves, along with adiabatic and vertical excitation energies, are presented with experimental comparisons. We predict Te values for A′5Σg+ and C″5Πu approximately 1 eV lower than indirectly derived "experimental" values. Dissociation energies computed with several ground-state wave functions illustrate the necessity for reaching basis set limits in analyzing contributions to an observable. © 1982 American Chemical Society.