A High-Density Supercritical Fluid of H₂

X-ray diffraction was performed on SCF H₂ using synchrotron radiation at room temperature. The structure factor <i>S</i>(<i>Q</i>) was observed in a low-<i>Q</i> region at each pressure, revealing a crossover at around 0.56 GPa, consistent with our previous Raman spectroscopy results.

The average volume per molecule was calculated at each pressure using the center-to-center distance between the nearest neighboring H₂ molecules, reflecting van der Waals interactions and compression of the internuclear distance. The volumes calculated from the face-centered cubic model were consistent with those derived from the cited equation of state, with a slight discrepancy that increased gradually with the pressure.