Communication: A simple full range analytical potential for H2 b3 ∑ u +, H-He 2∑+, and He 2 1 ∑ g +

Abstract

The Tang-Toennies potential for the weakly interacting systems H2 b3 Σ u +, H-He 2Σ+, and He 2 1 Σ g + is extended down to the united atom limit of vanishing internuclear distance. A simple analytic expression connects the united atom limiting potential with the Tang-Toennies potential in the well region. The new potential model is compared with the most recent ab initio calculations for all three systems. The agreement is better than 20% (H2 and He2) or comparable with the differences in the available ab initio calculations (H-He) over six orders of magnitude corresponding to the entire range of internuclear distances.