THE METHOD OF OSCILLATING INTERACTING DIPOLES AND THE VIBRATIONAL SPECTRA OF SOME ORGANIC AND METAL POLYCARBONYL DERIVATIVES

Abstract

The method of oscillating dipoles, in which the carbon and oxygen motion in a carbonyl stretching mode is replaced by a vector representing the oscillating dipole induced from such motion, is used to represent the normal modes of some organic and inorganic polycarbonyl derivatives. Metal pentacarbonyl halides of group VII:a elements $show^{1}$ one less main absorption band than expected in the $C \equiv O$ stretching region. The above method is used and shows at least qualitatively, that the two infrared active $a_{1}$ modes have the same intensity and are accidentally degenerate. The situation can thus lead to quantum mechanical interaction. The analysis of the situation $concludes^{2}$ that generally when tow accidentaly degenerate fundamentals with the same intensity interacts, only one infrared band appears with twice the intensity of either of the zero order fundamentals. From the relative position of the two carbonyl groups, the model predicts the relative position and activity of the infrared and Raman bands of organic dicarbonyls with two unconjugated nearby fixed carbonyl groups. The fact that planar $O = C \diamondsuit$ has a carbonyl $frequency^{3} (1783 cm^{-1})$ in between the high energy Raman active $(1860 cm^{-1})$ and the low energy infrared active $(1730 cm^{-1})$ modes of the planar dicarbonyl $O = C \diamondsuit C = O$ can easily be seen from the model. Other examples will be discussed.