| We have constructed a facility that is capable of studying materials at high pressure using nuclear magnetic resonance spectroscopy (NMR). A novel gasket, the split gasket, has been developed that has been used to contain samples to at least 25 GPa. When used in conjunction with a split cover inductor (together forming the "split gasket resonator") it allows for unprecedented increase in sensitivity (a factor of 50-100) for measurement of NMR when compared to previous NMR methods in a diamond anvil cell (DAC). A technique for loading hydrogen samples in our NMR cryostat has been developed that allows us to keep the pressurized sample at low temperatures and inside the cryostat at all times.; To demonstrate and test our facility, we performed an experiment studying the spin-lattice relaxation times (T{dollar}sb1{dollar}) of cyclohexane as a function of pressure to 97kbar at 77 K.; As the principal objective of this program, we have measured the ortho-para conversion of hydrogen as a function of pressure to 129kbar and to liquid helium temperature using NMR. The rate constant, which is 1.9%/hour at zero-pressure (this term is used by high-pressure physicists to denote atmospheric pressure), increases to almost 60%/hour at our highest pressure. We have also measured T{dollar}sb1{dollar} and T{dollar}sb2sp*{dollar} at various pressures, temperatures, and ortho concentrations. |
