Enhancement of Infrared Absorption Bands of Charge Transfer Complexes

Abstract

An enhancement of infrared absorption bands is shown to be inherent in charge-transfer theory due to change in vertical ionization energy or change in vertical electron affinity during the course of molecular vibration. A semiquantitative calculation of the intensity enhancement of the symmetric ring stretching vibrational mode of benzene in the benzene-iodine complex agrees well with the experimentally observed value. This result shows that previous investigators' assumptions of charge-transfer complex asymmetry, based on observed infrared absorption bands may not be valid.