Infrared Linear Dichroism in Stretched Films: Quantum Mechanical Approach Within the Polarizable Continuum Model

In this work we discuss how environmental effects on vibrational transition moment directions for molecules dispersed in stretched films can be accounted for via the integral equation formalism polarizable continuum model (IEFPCM). In particular, effects related to the matrix polarization induced by the probing field (cavity field terms) are taken into account. Calculations are performed for three DNA-related molecules (9-methyladenine, 7-methyladenine, and 2-amino-9- methylpurine) for which infrared linear dichroism (IR LD) has been measured experimentally. By combining experimental data and calculations, different parameters of the film (Saupe order parameters and orientational axis direction) can be obtained and used to give “experimental” estimates of transition moment directions. The results show the importance of accounting for the environment surrounding the molecule in transition moment calculations.