Global ab initio potential energy surfaces for both the ground ((X)over-tilde1 A′) and excited ((A)over-tilde1 A") electronic states of HNO and vibrational states of the Renner-Teller (A)over-tilde1 A"-(X)over-tilde1A′ system

The global potential energy surfaces for both the ground ((X) over tilde (1) A') and excited ((A) over tilde (1) A '') electronic states of the HNO molecule have been constructed by three-dimensional cubic spline interpolation of more than 17 000 ab initio points, which have been calculated at the internal contracted multi-reference configuration interaction level with the Davidson correction using an augmented correlation-consistent polarized valence quadruple zeta basis set. The low-lying vibrational energy levels for the two electronic states of HNO have also been calculated on our potential energy surfaces including the diagonal Renner-Teller terms. The calculated results have shown a good agreement with the experimental vibrational frequencies of HNO and its isotopomers. (C) 2011 American Institute of Physics. [doi:10.1063/1.3632994]