Rototranslational absorption in gaseous H2–Ar mixtures at intermediate densities

We present the measurements and analysis of the density effects on the rototranslational absorption spectrum of H2–Ar mixtures, for densities up to about 200 amagat. This density range is intermediate between the low-density limit, in which the spectrum is due to binary interactions, and the high-density range, in which density produces the so-called density-narrowing effect, which was studied previously. We find in the density range currently explored that density (ρ) effects are clearly evident and are well accounted for by considering a negative ρ3 contribution to the absorption besides the dominant ρ2 contribution. Experimental values of the two-body and three-body zeroth moments are obtained. We also obtain experimental line profiles for these two contributions. Even if the accuracy of the ρ3 profile is low, this work presents the first ρ3 line determined from measurements of collision-induced absorption.