Density dependence of pressure induce shifts of HCl rotational line perturbed by argon

Abstract

The density dependence of the pressure induced shift of the HCl pure rotational lines, perturbed by argon, has been measured. The shifts were measured for the rotational transitions J → J + 1, with J from 1 to 9, at a temperature of 162.5 K and argon densities between 39 and 480 amagat. In this density regime, the HCl rotational linewidths are known to depend non-linearly on the density. It is observed that most of the rotational lineshifts show no significant deviation from a linear density dependence. It therefore seemed justified to determine lineshift cross sections from the slopes of the straight lines that fitted the measured shifts best. The magnitude of the cross sections thus determined is significantly larger than has been predicted. The relevance of the lineshift cross sections for the determination of the HCl---Ar intermolecular potential is discussed. A possible explanation for the qualitatively different density dependence of lineshifts and linewidths is indicated