Infrared vibrational intensities and polar tensors of the carbonyl and thiocarbonyl halides

Abstract

The polar tensors of F 2CO, Cl 2CO, F 2CS and Cl 2CS have been determined from experimental infrared intensities. The sign ambiguities in the dipole moment derivatives were resolved by comparing alternative polar tensor solutions with the results of MP2 6-31G ∗ molecular orbital calculations using bidimensional principal component projections of the polar tensor spaces. The signs chosen for the dipole moment derivatives are the same as those chosen in an earlier work where CNDO estimates were used for comparison. Signs for derivatives related to very small intensities (< 0.5 km mol −1) were left undetermined. As already noted before the polar tensor for an atom of one of these carbonyl or thiocarbonyl halides can be estimated from the atomic polar tensors of the other three molecules. This is also true for the mean dipole moment derivatives and infrared intensity sums of these molecules. These simple relations can be explained if one assumes no saturation effect on the capacity of the carbon atom to donate electron density to the terminal atoms. Furthermore these simple relations appear to be extendable to the 1s core electron energies of these molecules if the mean dipole moment derivative values are used as atomic charges in the simple potential model.