Knowledge Bank

We present {ab initio} potential surfaces and rovibrational levels for He-CO, Ar-HCCH, and Ar-HCN. The intermolecular potentials are calculated using $M\backslash o$ller-Plesset perturbation theory up to the complete fourth-order (MP4) and efficient basis sets containing bond functions. The rovibrational energies and spectroscopic constants are calculated using the collocation method with the potential values at the collection points given by spline interpolation or by an analytical fit to the {ab initio} values. For He-CO, the potential surface is consistent with the $V3,3,3$ potential of Chuaqui and Le $Roy1$ but differs significantly from the latest empirical (XC) potential of Le Roy{ et al}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ and an earlier {ab initio} $calculation.3$ The energy levels predicted from our potential are compared with experiment. For Ar-HCCH, our potential shows a very flat minimum region from $\theta =70\circ$ to $110\circ$ (energy change $\le 1.0cm-1)$ in contrast to a high barrier $(25cm-1$) of the recent empirical potential by Bemis {et al}.$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$ The energy levels and spectroscopic constants predicted from our potential are compared with experiment. For Ar-HCN, we explicitly considered the effect of HCN bending vibration on the global potential and particularly on the potential anisotropy. The energy levels and spectroscopic constants arising from the calculated potential are compared with experiment.