Vibrational Structuring in Optical Activity

Abstract

The role which vibration can play in the ultraviolet- visible-range manifestations of optical activity is considered. The rotatory strength for individual vibronic bands as well as the rotatory strength integrated over all vibrational structure is developed. Rotatory strength of mixed sign appears as the analog of mixed polarization in ordinary absorption. Such developments can be carried out within the Born-Oppenheimer adiabatic approximation or in a manner appropriate to pseudo-Jahn-Teller effects. It can be shown that the study of vibronic structuring in circular dichroism, for example, can materially aid the assignment of vibrations, the assessment of the degree of “forbidden” character, the identification of “hot bands,” andthe analysis of strong, intermediate, and weak vibronic coupling with near-degenerate electronic levels. Some experimental examples are considered.