Centrifugal distortions in molecules: An ab initio approach with application to water

Abstract

Our procedure for employing analytical gradients of ab initio potential energy hypersurfaces in the description of centrifugally distorted molecules is applied to an asymmetric top, namely water. Both single determinantal ( HF /6-31G**) and configuration-interaction ( CISD /6-31G**) surfaces were utilized. Quartic centrifugal spectroscopic coefficients are obtained in both cases and are in reasonable agreement with experiment. It is shown that the calculated dependence of the energy upon the rotational angular momentum is better represented by a PadÉ approximant than by the conventional power series.