Using double-zeta plus polarization (DZP) basis sets systematically augmented with a variety of bond functions, the term dissociation energies are calculated for the A3Σ+ u, B3Πg and W3Δu states of N2. 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 B3Πg 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 ωe, ωeχe, ωeye, Be and αe and the dissociation energy De (e.g., De = 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.

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Journal Chemical Physics
Wright, J.S, Barclay, V.J., & Buenker, R.J. (Robert J.). (1987). Bond functions in molecular excited states: MRD CI calculations for the A3Σ+ u, B3Πg and W3Δu states of N2. Chemical Physics, 115(1), 23–32. doi:10.1016/0301-0104(87)80175-1