Computational and experimental investigation of intermolecular states and forces in the benzene–helium van der Waals complex

A study of the intermolecular potential-energy surface ~IPS! 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 twoto 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 approximation! calculations of J50 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. © 2003 American Institute of Physics. @DOI: 10.1063/1.1628217#