Vibrational Structuring in Optical Activity. I. Vibronic Coupling in the Circular Dichroism of Dimers

Abstract

The characteristics of circular dichroism arising from near‐degenerate electronic states under the influence of vibration are considered and compared to the ordinary absorption. A ``pseudo‐Jahn—Teller effect'' operates between limits of strong and weak coupling, the influence of which on ordinary absorption has been considered earlier. An exciton or coupled‐oscillator model is used which seems especially appropriate to optically active biaryls. For intermediate coupling, overlapping band systems of equal net rotatory strength but opposite sign will give a resultant dichroism altogether different in appearance from the ordinary absorption.