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The first three-dimensional ab initio intermolecular potential energy surface of the Ar-CO van der Waals complex is calculated using the coupled cluster singles and doubles including connected triples model and the augmented correlation-consistent polarized valence quadruple zeta ͑aug-cc-pVQZ͒ basis set extended with a (3s3 p2d1 f 1g) set of midbond functions. The three-dimensional surface is averaged over the three lowest vibrational states of CO. Rovibrational energies are calculated up to 50 cm Ϫ1 above the ground state, thus enabling comprehensive comparison between theory and available experimental data as well as providing detailed guidance for future spectroscopic investigations of higher-lying states. The experimental transitions are reproduced with a root-mean-square error of 0.13 cm Ϫ1 , excluding states observed around 25 cm Ϫ1 above the ground state. The latter states are at variance with the experimentally deduced ordering.

A study of the intermolecular potential-energy surface ͑IPS͒ and the intermolecular states of the perprotonated and perdeuterated benzene-He complex is reported. From a fit to ab initio data computed within the coupled cluster singles and doubles including connected triples model for 280 interaction geometries, an analytic IPS including two-to four-body atom-atom terms is obtained. This IPS, and two other Lennard-Jones atom-atom surfaces from the literature, are each employed in dynamically exact ͑within the rigid-monomer approximation͒ calculations of Jϭ0 intermolecular states of the isotopomers. Rotational constants and Raman-scattering coefficients for intermolecular vibrational transitions are also calculated for each of the three surfaces. The calculated results are compared with experimental results reported herein pertaining to intermolecular Raman spectra of benzene-He. The calculated rotational constants are compared with experimental values from the literature. The fitted IPS of this work leads to calculated observables that match the experimental results very well. The IPSs from the literature are not as successful, specifically in regard to the intermolecular Raman spectra.

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