Infrared Q-branch absorption and rotationally-hindered species in liquids

Abstract

We show the interesting sensitivity of infrared Q-branch absorption of HCl in liquid Ar to anisotropic solute–solvent interaction potentials. Comparing the differences among potentials with the different simulated absorption profiles they yield to, it is feasible to extract well-founded conclusions on the main mechanisms contributing to absorption on the Q-branch region. Moreover, it is shown that the well-known Ar–HCl stable quasilinear configuration at low densities is to some extent preserved in the liquid phase. The sizes and orientations of these traces of complexes in the liquid resemble those of van der Waals complexes in low-density gases. Finally, we analyze the meaning of the observed rotational hindering of the molecular probe and its influence on the shape of near-infrared spectra.