Bond functions in molecular excited states: MRD CI calculations for the A 3Σ +u, B 3Π g and W 3Δ u states of N 2

Abstract

Using double-zeta plus polarization (DZP) basis sets systematically augmented with a variety of bond functions, the term dissociation energies are calculated for the A 3Σ + u, B 3Π g and W 3Δ u states of N 2. It is found that the best agreement with literature values is generally with a basis set composition of DZP augmented by a set of s, p and d orbitals at the bond midpoint. The excited state potential energy curves and spectroscopic constants for the B 3Π g state are calculated from this basis and compared with experimental values. Good agreement was obtained, considering the small basis set size, with the spectroscopic constants ω e, ω eχ e, ω e y e, B e and α e and the dissociation energy D e (e.g., D e = 3.38 (3.681, exp.), 4.75 (4.897) and 4.77(4.873) eV for the A, B and W stages, respectively). Poorer agreement was obtained for the term energy T′ 0 (7.92 versus 7.35 eV, exp., for the B state). The error in term energy arises largely from an error in the calculated 4S → 2D splitting (2.705 versus 2.383 eV, exp.), and shifting the potential curve for the B state by a constant amount leads to much improved agreement relative to the ground state. The counterpoise correction applied to the potential curve of the B state causes a drastic deterioration of the results and shows qualitatively incorrect behaviour, and is therefore not recommended for calculations of this type.