Broad and Comprehensive Approach to Evaluate Infrared Intensities at Atomic Level: The AC/DC Analysis

We present a complete theoretical protocol to split infrared intensity in terms owing to individual atoms in two different but related approaches: the Atomic Contributions (AC's) how how the entire molecule motion is noticed by the electronic structure of a single atom, and therefore reflected on the intensity. On the other hand, the Dynamic Contributions (DC's) show how the displacement of a single atom is noticed by the electronic structure of the entire molecule, and reflected on the IR intensity. The two analyses are complementary ways of partitioning the same total intensity, and conserve most of the features of the total intensity itself. Combined they are called the AC/DC analysis. These can be further partitioned following the CCTDP (or CCT) models regarding the population analysis chosen by the researcher. The main conceptual features of the equations are highlighted and representative numerical results are shown to support the interpretation of the equations. The results are invariant to rotation and translation and can readily be extended to molecules of any size, shape or symmetry. A fully automated protocol managed by Placzek program is made available, free of charge.