Determination of re, the Difference between the Equilibrium Internuclear Distances in the Two Electronic States of a Diatomic Molecule, from Intensities of Vibrational Bands

Abstract

A method for determining the value of re' - re, the difference between the equilibrium internuclear distance of two electronic states involved in a band system, from the intensity of vibrational bands is discussed. The value of Δre ≡ re' - re thus obtained can be used to give the value of equilibrium internuclear distance for any one of the two states involved provided the same is known for the other. The method consists of equating the Jarmain - Fraser theoretical expression for the ratio of the squares of the overlap integrals of the two bands having the same v' value to the ratio of their I/ν4 values, and solving it for Δre = re' - re. In some cases, where the variation of electronic transition moment is large, the values of Δre obtained in this way may be unexpectedly divergent among themselves. In such cases the pair of bands used for estimating Δre should be selected in such a way that the individual members should have the same r-centroid, rather than the same v' values.