Low-lying excited states of N3−

A b initio SCF molecular-orbital calculations on low-lying states of linear, symmetric N3− were performed with the Hunt–Hay–Goddard open-shell program. Both a [3s, 2p] basis contracted from a primitive (9s, 5p) Gaussian basis, and the same basis augmented by polarization functions [3s, 2p]+d, were employed at a fixed internuclear distance rN–N=2.225 a.u. in calculating vertical excitation energies for the following states: ...4σg2 3σu2 1πg4, 1Σ+g; ...1πg3 2π1u, 1,3Σ+u, 1,3Σ−u, and 1,3Δu; ⋅⋅⋅3σu1 ⋅⋅⋅2π1u, 1,3Πg; and ⋅⋅⋅4σ1g ⋅⋅⋅2πu1, 1,3Πu. The smaller basis [3s, 2p] was used in calculating energies of the 1Σ+g ground state and the 3Σ+u, 1,3Σ−u, and 1,3Δu states of linear, symmetric N−3 as a function of internuclear distance. The [3s, 2p] basis was also used in the ibmol program of Clementi and Mehl to calculate energies of the 1A1(1Σ+g) ground state and the following low-lying triplet states of bent N3−: 3B2(3Σu+), 3A2(3Δu), 3B2(3Δu), and 3A2(3Σ−u). The triplet-state energies of bent N3− were corrected by incorporating approximate configuration mixing. Comparison of calculated energies with absorption spectra of azide compounds shows only qualitative agreement, but supports the interpretation of McDonald, Rabalais, and McGlynn.