Infrared intensities: Polar tensors and charge flux parameters

Abstract

An attempt has been made to streamline the procedure for analysis of infrared intensities of fundamental bands through polar tensor calculations. Different methods used in the literature to calculate the rotational contributions have been compared and a correlation has been pointed out. Using the atomic charge model, a generally applicable expression relating an atomic polar tensor to the equilibrium atomic charges and their flux terms has been derived. The bond moment model has also been used to obtain an analogous expression relating the atomic polar tensor to the bond moments and their derivatives. However, the final equations of these two models indicate that, irrespective of the model chosen for the interpretation of infrared intensities, one would obtain identical information.

Applied quantum chemistry

“…This correction arises from the fact that the molecular electronic charge distribution does not follow the atomic displacements in a rigid manner. For the same reasons the fixed partial atomic charges model [282] of the IR intensities proved to be unsatisfactory [1132]. We note in passing that the equivalence of the simple bond dipole and the fixed partial charge models have been demonstrated by the fact that they lead to the same atomic polar tensor expressions [1132].…”

A reinterpretation of the infrared linear dichroism of oriented nucleic acid films and a calculation of some effective partial changes on the ribose phosphate backbone

“…Finally, the apparent nonphysical charges obtained as a result of our simple-minded calculation must be viewed as the "dynamic charges" that appear in the transition dipole moments (31,32) that can differ significantly from the equilibrium charges obtained from a molecular orbital calculation. Our imprecise knowledge of both the atomic displacements and atomic charges does not warrant at this point a more refined calculation based on the available data.…”