Non-adiabatic crossing of energy levels

Abstract

The crossing of energy levels has been a matter of considerable discussion. The essential features may be illustrated in the crossing of a polar and homopolar state of a molecule. Let ψ 1 ( x /R), ψ 2 ( x /R) be two electronic eigenfunctions of a molecule with stationary nuclei. Let these eigenfunctions have the property that for R≫R 0 , ψ 1 has polar characteristics, ψ 2 homopolar; while at R≪R 0 , ψ 2 has polar characteristics, ψ 1 homopolar. In the region R=R 0 these two eigenfunctions may be said to exchange their characteristics.