Interaction Induced Raman Light Scattering Studies of CH4/H2 Mixtures as a Function of Density

We have recently interrogated several binary supracritical mixtures by means of interaction-induced Raman light scattering originating from a probe molecule (supracritical methane) at a concentration of 10 mol % in a variety of supracritical solvent systems (e.g., Ar, CO2, CF4, etc.). In this paper we look at a very different kind of solvent, supracritical molecular hydrogen. It was chosen because of its well-known reorientational properties, i.e., quantum mechanical rotation in all phases (except perhaps metallic H2(s)). The results indicate that the I/d vs d plots are more complicated than earlier systems studied and give good evidence of additional numbers of H2 molecules clustered around the solute CH4. Hydrogen's absolute differential Raman rotational cross-section for ΔJ = 1 → 3 is very well known and combined with the cross-section of the methane probe molecules' ν1 symmetric stretching vibration, it was possible to quantify and compare the contributions of various mechanisms known to be present in interaction-induced Raman light scattering of a wide variety of solvents and to therefore judge their solvating capacities vis a vis CH4.