Very accurate potential energy curve of the He ₂ ⁺ ion

A very accurate ground-state potential energy curve (PEC) of the He ₂₊ molecule is calculated with 1200 explicitly correlated Gaussian functions with shifted centers in the range between 0.9 and 100 a ₀. The calculations include the adiabatic corrections determined for the ³He ⁴He ⁺, ³ He ₂₊, and ⁴ He ₂₊ isotopologues. The absolute accuracy of the PEC is better than 0.05cm ^-1 and that of the adiabatic corrections is around 0.01cm ^-1. The depths of the PECs augmented with the adiabatic corrections for the three isotopologues are: 19956.708cm ^-1 for ⁴ He ₂₊, 19957.054cm ^-1 for ³He ⁴He ⁺, and 19957.401cm ^-1 for ³ He ₂₊. The rovibrational energies are also determined. For ³He ⁴He ⁺ the computed rovibrational transitions corresponding to the = 1-0 band differ from the experiment by less than 0.005cm ^-1. For the rovibrational transitions corresponding to the = 23-22 band the difference is around 0.012cm ^-1. Presently, this represents the best agreement between theory and experiment for He ₂₊.