Knowledge Bank

An ab initio approach to the theoretical description of centrifugal distortions in molecules is $presented.1$ The method is based on the calculation of the electronic energy changes and gradients accompanying rotationally induced distortions. A centrifugal distortion pathway in nuclear coordinate space is defined. Results are presented at the $HF/6-31G\ast \ast$ level for $NH3,CH4,BF3$, and $SF6$, and at the Gullemin-Zener level for $H2+$. Quartic centrifugal distortion parameters are computed for each molecule, with distortion anisotropies presented in the form of tensor coefficients. Centrifugally induced electric dipole moment coefficients are presented for $CH4$ and $BF3$ together with dipole moment changes for $NH3$. Agreement with experiment and with conventional theoretical descriptions is generally quite satisfactory, particularly for the tensor coefficients representing the cubic anisotropy in the distortions of the spherical tops $CH4$ and $SF6$.