Raman Measurements of Hydrogen in the Pressure Range 0.2-630 kbar at Room Temperature

Raman spectra of fluid hydrogen at room temperature include rotational, ${S}_{0}(J)$, and vibrational bands, ${Q}_{1}(J)$. The rotational bands become diffuse between 0.2 and 55 kbar, the solidification point at 22\ifmmode^\circ\else\textdegree\fi{}C. Between 55 and 630 kbar, only ${Q}_{1}(J)$ was resolved. This band increases in frequency to 360 kbar, but the frequency decreases between 360 and 630 kbar. These phenomena are consistent with the softening of the molecular bond at high pressure.