Intracollisional interference in the pure rotational spectrum of HD: Determination of the permanent electric dipole moment

The intensity of the pure rotational absorption spectrum of gaseous HD is measured as a function of density for pure HD and HD-He and HD-Ar mixtures. The decrease in the absorption coefficient with increasing density is consistent with a destructive intracollisional interference between the transitions involving the permanent and collision-induced dipole moments. The permanent dipole moment of the molecule in its ground vibrational state is found to be J dependent and in the range (8-10)×{}10^-4 D.