Morphing the He–OCS intermolecular potential

A potential energy surface for He–OCS that agrees with experimental rotational spectra to within 1 MHz is presented. The potential was first calculated at a grid defined in prolate spheroidal coordinates, which give stabler interpolations than Jacobi coordinates. Coupled cluster calculations at the CCSD(T) level were carried out with an aug-cc-pVTZ basis set. The potential was then morphed, a procedure that scales the energy and the intermolecular distance in a coordinate-dependent way. The parameters of the function used for morphing were determined by a least-squares fit to the experimental data. The global minimum of the recommended potential, at −50.2 cm−1, is 4.8 cm−1 deeper than the unscaled potential of Higgins and Klemperer [J. Chem. Phys. 110, 1383 (1999)]. The morphing procedure increases the well depth by more at the sulfur end than at the oxygen end