T₁ relaxation of perylene in fluid ethane: Pressure-dependent changes in short-range organization

We report our measurements of vibrational population relaxation of the v₇ (1375 cm^-1) mode of perylene in ethane at a series of fluid pressures. The data show that T₁ decreases with increasing fluid pressure and that the dependence of T₁ on pressure is not consistent with predictions based on simple spatial or stoichiometric considerations. The data indicate a nonrandom orientational distribution of the solvent molecules about the solute where the portion of the solvent environment sensed by the perylene v₁ coordinate changes from one ordered state to another ordered state with increasing pressure.