Ab initio ground-state potential energy functions of beryllium monohydride ions: BeH+ and BeH-.

The accurate ground-state potential energy functions of beryllium monohydride (BeH) cation and anion have been determined from ab initio calculations using the multi-reference averaged coupled-pair functional (MR-ACPF) method in conjunction with the correlation-consistent core-valence basis sets up to septuple-zeta quality. The effects of electron correlation beyond the MR-ACPF level of approximation, as well as the scalar relativistic and adiabatic corrections were taken into account. The vibration-rotation energy levels of the BeH, BeD, and BeT isotopologues of both ions were predicted to near "spectroscopic" accuracy. The results can be useful in a future experimental detection of the BeH anion by high-resolution vibration-rotation spectroscopy.