In many spectral theories, the knowledge of the time autocorrelation functions associated with the solute-solvent intermolecular anisotropic potential is a necessary step to obtain the far-infrared (FIR) spectra of small polar diatomic molecules dissolved in a nonpolar solvent. Within the pairwise additive approximation, we have obtained these functions from a molecular dynamics simulation for HCI in fluid Ar (between 100 and 480 amagat) at T = 162.5 K. The simulated correlation functions are tested in the calculation of the pure far-infrared spectrum, appropriately described by a theory incorporating memory effects, line mixing effects, and the influence of any anisotropy order on the diatom-atom intermolecular potential. The comparison between the theoretical and experimental spectra allow us to obtain some conclusions about the relative importance of the first and second order anisotropic interaction correlations on the FIR spectra of HCI in dense Ar.