Interpretation of vibrational absorption intensities: Effective bond charges from rotation free atomic polar tensors

Abstract

Abstract In the present paper a new theoretical framework for analysis of vibrational intensities is presented. In a mathematically straightforward procedure corrected for various rotational contributions, atomic polar tensors are transformed into quantities termed effective bond charges. All rotational contributions to dipole moment derivatives are appropriately considered and eliminated from the equations. The effective bond charges are expected to reflect in a generalized manner polar properties of the valence bonds in molecules. Aside from the usual harmonic approximation no other constraints are imposed on the dipole moment function. The application of the formulation developed is illustrated with calculations employing atomic polar tensors for H 2 O, NH 3 , CH 4 , C 2 H 4 , C 2 H 2 and CH 2 O obtained from RHF/6-31G** ab initio calculations.