Experimental and theoretical investigation of the far-infrared spectrum of H2-He mixtures.

Abstract

New measurements of the rototranslational collision-induced absorption spectra in the far-infrared (FIR) frequency region of gaseous mixtures of hydrogen (${\mathrm{H}}_{2}$) and helium (He) are reported. The frequency range extends up to 1500 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at the temperature of 195 K, and 1700 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at 296 K. The uncertainties of the measurement are assessed. Comparison with previous measurements show substantial agreement at frequencies where the measurements overlap. For comparison with the measurement, spectra are computed from the fundamental theory using a state of the art ab initio dipole function and an isotropic potential surface as input. The observed agreement suggests that for important applications, such as the analysis of the FIR spectra of the outer planets, the spectra can be obtained reliably as a function of frequency and temperature from quantum calculations of the kind presented here.