A valence-bond diatomics-in-molecules model for the formation of Na+ and Na2+ ions from the interaction of excited sodium atoms with a tungsten surface

Potential energy surfaces for Na(²S, ²P) interacting with a partially covered tungsten surface are computed within the framework of the method of diatomics-in-molecules (DIM). Only two sodium atoms are considered explicitly but the effect of all of the adsorbed sodium is taken into account through its influence on the fragment matrix elements in the DIM formulation. Na₂⁺ wavefunctions are approximated by valence-bond calculations for the ²Σ_g⁺ and ²Σ_u⁺ manifolds. The three lowest potential energy surfaces of the polyatomic system suggest plausible pathways for the production of Na⁺ and Na₂⁺ ions from the interaction of Na(²P) atoms with the metal surface as observed by Auschwitz and Lacmann.