Ab initio/spectroscopic interaction potential for He+Ne+

High-level ab initio calculations have been carried out on the lowest Σ and Π states of HeNe+. These have been used to construct a new interaction potential in a Hund’s case (e) representation, by fitting spectroscopic vibrational spacings ΔGv+1/2 and rotational constants Bv using a close-coupling method and a potential function whose form is established by the ab initio data and a long-range analysis. The characteristics of the resulting Born–Oppenheimer potential curves, particularly for the X state, where only the higher vibrational levels were observed, differ considerably from those derived by extrapolation of the experimental spectroscopic constants. A new set of constants is proposed, and functions for the X-state G(v) and Bv are given that are well-behaved from the bottom of the well to the dissociation limit. The asymptotic formula for Bv of Le Roy is extended to improve its accuracy. The X state of HeNe+4 is predicted to support 15 bound vibrational states, the A2 state 7. Good agreement with experiment in magnitude and trends is found for spin-splitting and Ω-doubling constants. Comparison is made between energy levels calculated in the close-coupling formalism and in the customary case (c) Born–Oppenheimer approximation; the largest differences, which are readily resolved spectroscopically, are reflected in Bv for high vibrational levels of the X state, including those observed.