The H₂O-H₂O dispersion energy constant and the dispersion of the specific refractivity of dilute water vapour

Abstract

Several alternative dipole oscillator strength distributions for the ground-state water molecule are used to calculate the average long-range dispersion energy coefficient C ₆ for the interaction of a pair of water molecules and the dispersion of the specific refractivity of dilute water vapour. The distributions are based on different experimental photoabsorption and/or high energy inelastic scattering data for water vapour. Each distribution is required to satisfy the Thomas-Reiche-Kuhn sum rule and to yield the value of the static dipole polarizability, α _d = 1·427 × 10^-30 m³ (9·630 bohr³), which is obtained from an analysis of published refractive index and dispersion measurements on water vapour at visible and ultra-violet wavelengths. A comparison of the experimental and the calculated specific refractivities, as a function of wavelength, is used to assess the quality of each distribution. On the basis of this comparison a recommended value of the dispersion energy coefficient, C ₆ = 43·4 × 10^-79 J m⁶ (45·4 hartree-bohr⁶), is obtained. In addition a formula for the dispersion of the specific refractivity of dilute water vapour is given, in the Cauchy form, for wavelengths in the visible and near ultra-violet regions.

This research was supported by a grant from the National Research Council of Canada and grant 240 of the Ontario Treatment Research Foundation.

This research was supported by a grant from the National Research Council of Canada and grant 240 of the Ontario Treatment Research Foundation.

Notes

This research was supported by a grant from the National Research Council of Canada and grant 240 of the Ontario Treatment Research Foundation.

Additional information

Notes on contributors

William J. Meath

Associated with the Centre for Interdisciplinary Studies in Chemical Physics.