Infrared Intensity Sum Rule and Effective Charges

Abstract

By using a Cartesian coordinate system, it is shown that the sum of integrated infrared intensities is given by a very simple expression that depends upon atomic masses, effective charge parameters, and the molecular dipole moment, but is otherwise independent of molecular geometry. The application of this sum rule to the analysis of the intensities of the hydrocarbons reveals that the effective charge parameters are approximately transferable from one molecular system to another, with the possible exception of acetylene.