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 ...