THE GEOMETRIES AND THE INVERSION POTENTIAL FUNCTIONS OF FORMALDEHYDE AND THIOFORMALDEHYDE IN THE $\bar{A}^{1}A_{2}$ AND $\bar{a}^{3}A_{2}$ ELECTRONIC STATES

Abstract

We have developed the ""semirigid invertor"" Hamiltonian to calculate rotation-inversion energy levels for an $X_{2}YZ$ formaldehyde-type molecule. In this model, the bond lengths and XYX angle are allowed to very as functions of the inversion coordinate. This is an improvement over the rigid invertor Hamiltonian derived by $Kreglewski^{1}$. Least squares fits to the inversion-rotation energy levels of the $\bar{A}^{1}A_{2}$ and $\bar{a}^{3}A_{2}$ electronic states of $H_{2}CO, H_{2}^{13}CO, D_{2}CO, H_{2}CS$, and $D_{2}CS$ have been carried out, yielding the geometrical parameters and the effective inversion potential function for each molecule and electronic state. The barrier to planarity for formaldehyde was found to be $316 cm^{-1}$ in the singlet state and $762 cm^{-1}$ in the triplet state. This result does not agree with ab initio $calculations^{2}$. For thioformaldehyde, the barrier to planarity was found to be only $7 cm^{-1}$ in the triplet state, whereas the molecule is found to be planar in the singlet state.