Spin-rotation interaction in diatomic molecules

Abstract

The simple operator gamma N.S which is usually assumed to give a proper description of the first order spin-rotation interaction in diatomic molecules, is in the case of Sigma states shown to be strictly derivable from a fundamental microscopic Hamiltonian given by Van Vleck. In this derivation the electronic screening of the rotating nuclear charges is taken into account. For other types of states it is emphasized that this simple operator only represents an approximation to the true spin-rotation interaction Hamiltonian. Assuming the electronic functions to be given by a Slater determinant of one-electron molecular orbitals, a formula suitable for ab initio calculation of the coupling constant gamma is derived.