PUB - Publikationen an der Universität Bielefeld

We present a general procedure. based on the Holstein-Herring method. for calculating exactly the leading term in the exponentially small exchange, energy splitting between two asymptotically degenerate states of a diatomic molecule or molecular ion. The general formulae we have derived are shown to reduce correctly to the previously known exact results for the specific cases of the lowest Sigma and Pi states of H-2(+). We then apply our general formulae 2 to calculate the exchange energy splittincys between the lowest states of the diatomic alkali cations K-2(+), Rb-2(+) and Cs-2, which are isovalent to H-2(+). Our results are found to be in very good agreement with the best available experimental data and ab initio calculations.