Cross Second Virial Coefficients of the H2O–H2S and H2O–SO2 Systems from First Principles

The cross second virial coefficients B12 for the interactions of water (H2O) with hydrogen sulfide (H2S) and of water with sulfur dioxide (SO2) were determined at temperatures from 200 to 2000 K employing new intermolecular potential energy surfaces (PESs) for the H2O–H2S and H2O–SO2 molecule pairs. The PESs were fitted to interaction energies calculated for more than 50 000 configurations of each molecule pair using quantum-chemical ab initio methods up to coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] with consideration of relativistic effects. The B12 values were extracted from the PESs both classically and semiclassically using the Mayer-sampling Monte Carlo scheme. In addition, accurate correlations of the final B12 values were used to derive the dilute gas cross isothermal Joule–Thomson coefficients, ϕ12 = B12 – T(dB12/dT). For both investigated systems, Wormald provided the only experimentally based B12 and ϕ12 values available in the literature. While his B12 values, which he obtained from the ϕ12 data with the aid of model potentials, are not in satisfying agreement with the present B12 values, his ϕ12 data, after a reanalysis using more accurate pure-component ϕ values, agree very well with the calculated ϕ12 values of this work.