An accurate ab initio potential energy surface and calculated spectroscopic constants for BeH2, BeD2, and BeHD

A three-dimensional potential energy surface for the ground electronic state of BeH(2) has been determined by three-dimensional spline interpolation over 6864 symmetry-unique ab initio points calculated at the icMRCI/aug-cc-pV5Z level and corrected for core-electron correlation computed at the MR-ACPF/cc-pCV5Z level. Calculated spectroscopic constants of BeH(2) and BeD(2) are in excellent agreement with recent experimental results: for 11 bands of BeH(2) and 5 bands of BeD(2) the root mean square (rms) band origin discrepancies were only 0.15(+/-0.09) and 0.46(+/-0.19) cm(-1), respectively, and the rms relative discrepancies in the inertial rotational constants (B([v])) were only 0.028% and 0.023%, respectively. Spectral constants for BeHD were predicted using the same potential surface. The effect of different interpolation methods on predicted potential function values and on the calculated level energies and spectroscopic constants has been examined.