Experimental compressions for normal hydrogen and normal deuterium to 25 kbar at 4.2 K

The piston-displacement technique has been used to determine the pressure-volume relations for normal hydrogen ($n\ensuremath{-}{\mathrm{H}}_{2}$) and normal deuterium ($n\ensuremath{-}{\mathrm{D}}_{2}$) at pressures to 25 kbar at 4.2 K. The accuracy of the relative compressions $\frac{V}{{V}_{0}}$ ranges from \ifmmode\pm\else\textpm\fi{}${10}^{\ensuremath{-}3}$ at low pressures to \ifmmode\pm\else\textpm\fi{}3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ at 25 kbar. The data, especially for $n\ensuremath{-}{\mathrm{H}}_{2}$, agree well with earlier 20-kbar results, and the extrapolated $P=0$ bulk moduli, 1.70 \ifmmode\pm\else\textpm\fi{} 0.06 kbar for $n\ensuremath{-}{\mathrm{H}}_{2}$ and 3.15 \ifmmode\pm\else\textpm\fi{} 0.06 kbar for $n\ensuremath{-}{\mathrm{D}}_{2}$, are consistent with recent ultrasonic data. The shapes of the pressure-volume relations resemble more closely those for the helium isotopes than those for the heavier-rare-gas solids, and suggest that the two-body repulsive interaction for hydrogen molecules (and helium atoms) varies more slowly with intermolecular spacing than that for the heavier-rare-gas atoms. These experiments also give maximum values for the pressure-dependent shear yield stress of solid hydrogen.

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