  Gaseous mixtures of water vapor and neutral molecules of salt (e.g., NaCl,
CuCl etc.) can be highly non-ideal due to the strong attractive interaction
between salt and water molecules. In particular, this can result in high
solubility of salts in water vapor and a strong dependence of solubility on
vapor pressure. The analysis of salt solubility in water vapor can be done
using the Pitzer-Pabalan model, which is based on the thermodynamic theory of
imperfect gases. The original Pitzer-Pabalan work demonstrated that one can
reproduce experimental data for NaCl solubility in vapor. No analysis was
performed on the reliability of their original fits, which we believe has
contributed to the lack of applications of the Pitzer-Pabalan model despite the
apparent success of the original paper. In this work, we report recent progress
in developing a rigorous fitting procedure to parameterize the Pitzer-Pabalan
model using experimental data. Specifically, we performed fitting of the
experimental results obtained elsewhere for NaCl and CuCl. We investigate the
degree of underfitting/overfitting and the sensitivity of the fitting quality
to variations in the resulting fitting parameters. The results, as represented
by the thermodynamic parameters describing the energetics of formation of
salt-bearing water clusters, were successfully benchmarked against Gaussian 16
ab initio quantum chemistry calculations. The resulting rigorous fitting
procedure presented here can now be applied to other systems.
