Nonorthogonal configuration-interaction calculations of molecular states: The low-lying molecular states of ArHsup+ and two-electron charge exchange in Ar-H\u3csup\u3e+\u3c/sup\u3e collisions

A nonorthogonal configuration-interaction procedure has been used to calculate adiabatic energy curves of ArH+. The basis functions are a mixture of typical molecular-orbital configurations and typical valence-bond (Heitler-London) configurations. This gives an economical description of the wave functions, allowing an easy tracing of various diabatic states through the adiabatic states and a clear identification of the asymptotic states. The results are used to rationalize the unexpectedly large production of Ar2++H- from collisions of H+ with Ar