On the nature of the background absorption in vibrational overtone spectroscopy

Abstract

A general coupling scheme between the X-H local modes and the collection of normal modes of a polyatomic molecule, due to the kinetic and potential energy interactions, is presented. Numerical calculations performed for benzene indicate the relatively strong effects of the kinetic energy coupling on the overtone absorption spectrum. The dipole forbidden transitions to the combined local and normal states borrow intensity from the dipole allowed transitions to the overtones and can give a contribution to the observed background absorption.