Cross Second Virial Coefficients of the H 2 O-H 2 and H 2 S-H 2 Systems from First-Principles.

The cross second virial coefficients B 12 for the interactions of water (H 2 O) with molecular hydrogen (H 2 ) and of hydrogen sulfide (H 2 S) with H 2 were obtained at temperatures in the range from 150 to 2000 K from new intermolecular potential energy surfaces (PESs) for the respective molecule pairs. The PESs are based on interaction energies determined for about 12 000 configurations of each molecule pair employing different high-level quantum-chemical ab initio methods up to coupled cluster with single, double, triple, and perturbative quadruple excitations [CCSDT(Q)]. Furthermore, the interaction energies were corrected for scalar relativistic effects. Both classical and semiclassical values for B 12 were extracted from the PESs using the Mayer-sampling Monte Carlo approach. While our results for the H 2 O-H 2 system validate the older first-principles results of Hodges et al. [J. Chem. Phys. 2004 , 120, 710-720], B 12 for the H 2 S-H 2 system was, to the best of our knowledge, hitherto neither measured experimentally nor predicted from first principles.