Variational calculation of low-lying and excited vibrational levels of the water molecule

Abstract The variational method of calculating vibrational energy levels for triatomic molecules has been extended to determine the lowest 22 levels for H 2 O, using an analytic form for the potential surface developed by Sorbie and Murrell. In addition, complete ab initio calculations of the fundamental frequencies for H 2 O have been carried out using extensive configuration interaction forms for the potential. They are predicted to be 3720, 1629, and 3807 cm −1 , to be compared with experimental values of 3656, 1597, and 3754 cm −1 . Also discussed is how the variational method may be extended to allow the calculation of vibrational energy levels for larger molecules.