Dipole spectrum, sums and properties of ground-state methane and their relation to the molar refractivity and dispersion energy constant

Abstract

Experimental and theoretical photo-absorption and high energy inelastic electron scattering cross sections, together with refractivity and sum rule constraints, are used to construct the non-relativistic dipole oscillator strength distribution (DOSD) for ground-state CH₄. The DOSD is used to evaluate a number of useful dipole oscillator strength sums. For example, these results give the mean excitation energies (estimated error 4 in the Bethe-Born approximation. The DOSD is also used to evaluate the molar refractivity, as a function of wavelength, in the ultra-violet and visible spectral region, and to obtain an accurate result (estimated error C ₆, for the CH₄-CH₄ interaction. Experimental band intensities are used to evaluate the infra-red contribution to both C ₆(CH₄-CH₄) and the dipole polarizability of methane. Finally combination rule values of C ₆(CH₄-B), for B=H₂, N₂, O₂, NH₃, H₂O, NO, N₂O and He are obtained by using C ₆(CH₄-CH₄) and accurate literature values for C ₆(B-B).