A HIGH-PRESSURE STUDY OF ORTHO-PARA CONVERSION IN HYDROGEN BY NMR

We have developed a system for studying NMR in a diamond anvil cell (D AC) resulting in an increased sensitivity of a few orders of magnitude . The DAC was loaded with solid hydrogen and studied to a pressure of 12.8 GPa in the temperature range of 4.2 to 77.3 K. We measured free i nduction decays and spin echoes. From this we could determine the orth o-para conversion rate. Conversion measurements were made at both low and high temperatures and are possible because at high pressure the sa mple remains solid. The rate constant rises to 58 %/hr at our highest pressure.