A new computational tool for interpreting infrared spectra of molecular complexes

The popularity of the Infrared (IR) spectroscopy is due to its high interpretive power. This study presents a new computational tool for analyzing the IR spectra of molecular complexes in terms of intermolecular interaction energy components. In particular, the proposed scheme enables to associate the changes in IR spectra occurring upon the complex formation with individual types of intermolecular interactions (electrostatic, exchange, induction, dispersion), thus providing a completely new insight into the relations between the spectral features and the nature of cohesive forces in molecular complexes. To demonstrate its interpretive power, we analyze which interaction types govern the IR intensity changes for selected vibrational modes upon the formation of a complex of benzene and 1,3,5-trifluorobenzene representing π···π stacking structural motif.