The vibrational Raman spectrum of compressed solid hydrogen

Abstract

The frequencies of the pure vibrational lines, Q(0) and Q(1), in the Raman spectrum of solid H2 have been measured when the solid was subjected to a number of pressures between 400 and 1000 kg cm−2, corresponding to solid densities up to ~ 1250 amagat. Most samples studied had orthohydrogen concentrations ≥ 0.60. For these the frequency of Q(0) increased as the density increased but that of Q(1) showed little change. This can be explained if it is assumed that (i) the isotropic repulsive overlap interaction between a pair of molecules increases more rapidly than the attractive dispersion-type interaction, (ii) the effect of vibrational coupling between molecules in the same J-state increases asp2, and (iii) the lowering of the excitation energy of the ν = 1,J = 1 stale by electric quadrupolar interactions increases as ρ5/3. There is evidence that at higher densities ordering of the molecular angular momenta may occur at temperatures up to 4 K. The intensity of Q(1) relative to Q(0) is further enhanced at higher densities.