Molecular study of outer K-L shell interactions: the Na-He collisional system

A Feshbach projection operator technique involving self-consistent field (SCF) calculations in orthogonal subspaces is used to obtain diabatic orbitals of the Na-He collisional system. Analysis of the molecular orbital wavefunctions and their delta / delta R couplings show that the Barat-Lichten correlation rule for the promoted orbital is incompatible with the diabatic smoothness criterion. The previously admitted conjecture that the strong asymmetry of the system would lead to an adiabatic behaviour of the sigma 1s He - sigma 3s Na molecular orbital (MO) crossing is not supported by the presently calculated coupling matrix elements. The molecular mechanism for Na(3s to 3p) excitation appears to be induced indirectly (as for Na-Ne collisions) by two successive curve crossings via the core-core K-L shell interaction.