MRCISD and GVVPT3 study of the low-lying electronic states of NO−

Abstract

The ground electronic state (X 3Σ−) and three low-lying excited electronic states, 11Σ+, 11Δ, and 13Π, of NO− were studied using MRCISD and GVVPT3 with the aug-cc-pVXZ (X = D, T, Q) basis sets and extrapolated to complete basis set limits. The thermodynamic constants, re , ωe , ωexe , and De , are predicted to be in good agreement with experimental values, where available. The increase of basis set lowers substantially the potential well of 13Π with respect to the ground state, e.g. the value of Te , 18425 cm−1 by MRCISD/aug-cc-pVDZ, decreases to 10829 cm−1 by MRCISD at the complete basis set limit. Additional calculations, using perturbative corrections for triple and quadruple excitations to MRCISD, i.e. MRCISD(TQ), showed that inclusion of triples and quadruples are essential to predictions of the electron affinity of NO, resulting in an increase in electron binding of over 0.36 eV.