INFRARED VIBRATIONAL INTENSITIES AND POLAR TENSORS OF THE CARBONYL AND THIOCARBONYL HALIDES

The polar tensors of F2CO, Cl2CO, F2CS and Cl2CS have been determined from experimental infrared intensities. The sign ambiguities in the di pole moment derivatives were resolved by comparing alternative polar t ensor solutions with the results of MP2/6-31G molecular orbital calcu lations using bidimensional principal component projections of the pol ar tensor spaces. The signs chosen for the dipole moment derivatives a re the same as those chosen in an earlier work where CNDO estimates we re used for comparison. Signs for derivatives related to very small in tensities (<0.5 km mol(-1)) were left undetermined. As already noted b efore the polar tensor for an atom of one of these carbonyl or thiocar bonyl halides can be estimated from the atomic polar tensors of the ot her three molecules. This is also true for the mean dipole moment deri vatives and infrared intensity sums of these molecules. These simple r elations can be explained if one assumes no saturation effect on the c apacity of the carbon atom to donate electron density to the terminal atoms. Furthermore these simple relations appear to be extendable to t he Is core electron energies of these molecules if the mean dipole mom ent derivative values are used as atomic charges in the simple potenti al model. (C) 1997 Elsevier Science B.V.