Three Sum Rules for Total Optical Absorption Cross Sections

Abstract

A sum rule is proved for the total optical absorption cross section for a system of interacting polarizable particles, each of which may have a total charge, a dipole moment, and an arbitrary mass distribution. This sum rule may be applied to the measurement of dipole moments of molecules or ions. The total absorption intensity due to an internal transition in a system of interacting asymmetric rotors is calculated. The first moment of the absorption intensity distribution about an internal transition is found for a system of interacting asymmetric rotors. This rule may be used to determine the true internal transition energy from an absorption spectrum.