Vibrational intensities of F2CS and Cl2CS

The CNDO approximate molecular wavefunctions for F₂CS and Cl₂CS have been applied to the calculation of the derivatives of the dipole moment with respect to the symmetry coordinates. Unique sets of experimental derivatives in the A₁ symmetry species of these molecules are definitely preferred according to these calculations. Two experimental sets of derivatives in the B₁ symmetry species of each molecule are consistent with the calculated results. All the preferred experimental derivatives for the stretching coordinates, ${\mathrm{\partial \; p/\partial \; r}}_{\mathrm{CF}}$ and ${\mathrm{\partial \; p/\partial \; r}}_{\mathrm{CCl}}$ , and the in‐plane bending coordinate, $\mathrm{\partial \; p/\partial \alpha }$ , have negative signs. The CF out‐of‐plane bending derivative in F₂CS appears to be negative although the corresponding CCl derivative is probably positive. The theory qualitatively reflects trends in the magnitudes of these derivatives in the different X₂CY molecules and in different symmetry species of the same molecule. Empirical equations of the type ${\mathrm{(\partial \; p/\partial \; r}}_{\mathrm{CCl}}{{)}_{{\mathrm{Cl}}_2}}_{\mathrm{CS}}{\mathrm{-(\partial \; p/\partial \; r}}_{\mathrm{CF}}{{)}_{{\mathrm{F}}_2}}_{\mathrm{CS}}{\mathrm{=(\partial \; p/\partial \; r}}_{\mathrm{CCl}}{{)}_{{\mathrm{Cl}}_2}}_{\mathrm{CO}}{\mathrm{-(\partial \; p/\partial \; r}}_{\mathrm{CF}}{{)}_{{\mathrm{F}}_2}}_{\mathrm{CO}}$ , relating corresponding derivatives for F₂CO, Cl₂CO, F₂CS, and Cl₂CS, are discussed.