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

Abstract

Our procedure for employing analytic gradients of ab initio potential energy hypersurfaces in the description of centrifugally distorted molecules is applied to a symmetric top, namely phosphine. Quartic centrifugal spectroscopic coefficients are obtained and are in excellent agreement with the coefficients from the Kivelson and Wilson method for J || z. We proposed a Borel form that enables us to fit the stabilization energies up to J = 80 for the vibrational ground state of phosphine. The sextic spectroscopic constant for J || z is obtained. Both single determinantal (HF/6-31G**) and multideterminantal Moller-Plesset (MP2/6-31G*) surfaces were utilized.