The Melting Line of Molecular Hydrogen at High Pressure

We have measured the melting line of molecular hydrogen to pressure P=82 GPa in a diamond anvil cell (DAC) using pulsed laser heating and found a peak at P=64.5$\pm$4 GPa and T=1055$\pm$20 K. Previous attempts to measure the melting temperature of hydrogen in a DAC by CW ohmic heating methods were limited by the diffusion of hydrogen at elevated temperatures. We have developed a technique of temperature determination in a pulsed laser heated DAC and succeeded to achieve much higher pressures and temperatures. In the pulsed laser method hydrogen diffusion is suppressed allowing access to high temperatures at elevated pressures.