Measurements and analysis of rototranslational absorption spectra of low density H2–Ar mixtures

We present new measurements of the rototranslational absorption of H2–Ar mixtures at 195 and 298 K. Measurements were made at densities as low as possible. The first accurate (5% error) rototranslational spectrum of the H2–Ar pair was thus derived. We performed a line-shape analysis of these spectra; as a result, we found a low-frequency component associated with an isotropic overlap induced dipole. We also found an important anisotropic overlap contribution associated with the dominant quadrupolar induction. Through a spectral-moment analysis we determined the intensity of isotropic (λ0 = 2.35 ± 0.15 × 10−3ea0) and anisotropic (λ1 = 0.9 ± 0.1 × 10−3ea0) overlap induced dipoles. The range of the isotropic overlap induced dipole was found to be ρ0 = (0.105 ± 0.010)σ, in very good agreement with the value 0.11 σ frequently assumed in the literature for the range of overlap induced dipoles. Our measurements and the results of our analysis were in good agreement with results of recent computations.