INTERMOLECULAR FORCES IN WATER VAPOR

Vapor-phase thermodynamic and transport properties at low to moderate densities were analyzed to determine intermolecular forces and hydrogen bonding of pure water vapor. Hydrogen-bond energies up to about -6 kcal. per mole for an open-chair dimer model are consistent with experimental second virial coefficient and heat capacity data. In addition, Stockmayer potential parameters fitted to the data indicate that the energy parameter should be less than 300° K., while the distance parameter is between 2.68 and 3.00 A. These values appear more consistent with the structure of water than previous ones which ignored hydrogen-bonding and induction forces. However, the pure component data are not sufficiently sensitive to the potential to be able to establish the parameters more closely. Analysis of the anomalous effect of pressure on the viscosity of water vapor indicates that further theoretical work may be needed to explain the experimental temperature dependence, although hydrogen bonding is apparently not inconsistent with the observed effect. © 1969, American Chemical Society. All rights reserved.