Application of a reflection principle to spectroscopic transitions in molecular dimers

Absorption spectra of molecular dimers are calculated within the reflection approximation which ignores the kinetic energy operators in the respective Hamiltonians. In treating a single vibrational degree-of-freedom for each monomer unit, it is found that band positions and band shapes are excellently reproduced as compared to the numerically exact calculation. In particular, it is shown that the spectra originating from the coupled electronically excited states can be related to the probability density of the initial wave function in the ground electronic state along a single center-of-mass coordinate.