An ab initio global potential-energy surface for NH2(A2A') and vibrational spectrum of the Renner-Teller A2A'-X2A' system

A global potential-energy surface for the first excited electronic state of NH2(A(2)A(')) has been constructed by three-dimensional cubic spline interpolation of more than 20 000 ab initio points, which were calculated at the multireference configuration-interaction level with the Davidson correction using the augmented correlation-consistent polarized valence quadruple-zeta basis set. The (J=0) vibrational energy levels for the ground (X(2)A(')) and excited (A(2)A(')) electronic states of NH2 were calculated on our potential-energy surfaces with the diagonal Renner-Teller terms. The results show a good agreement with the experimental vibrational frequencies of NH2 and its isotopomers.