The electron-pair density distribution of the 1,3Π u excited states of H2.

The non-monotonic behavior of the electron repulsion energy and the inter-electronic distance, as a function of the internuclear separation, in the 3Π u excited state of the hydrogen molecule has been assessed by explicit calculation and analysis of the electron-pair density distribution functions from high level ab initio full configuration interaction wave functions, for both the 3Π u and the 1Π u states. Additionally, Hund's rule as applied to these two states has been accounted for in terms of simple electronic shielding effects induced by wave function antisymmetrization. [ABSTRACT FROM AUTHOR]