Nuclear Magnetic Resonance Study of Methane Adsorbed on Graphite.

We have measured the spin-spin and spin lattice relaxation times of methane adsorbed on Grafoil, an exfoliated graphite, using pulsed nuclear magnetic resonance techniques. Data were taken between 45K and 105K and between 0.20 and 1.1 monolayers at frequencies of 4.586 and 2.107 MHz. In addition, proton relaxation times were measured with mixtures of 50% CD(,4) + 50% CH(,4). It was determined by the CD(,4) dilution experiments that relaxation was via intramolecular dipolar interactions. Activation energies, which were computed from the T(,1) data, provide evidence for both coverage-driven (at 0.87 monolayers) and temperature-driven (at (TURN)65K, coverage dependent) commensurate-incommensurate phase transitions. A frequency independent jump in T(,1) at lower coverages indicates first order melting to the liquid at approximately 57K. Higher temperature data find supporting evidence for a hypercritical fluid (2D gas) above a critical temperature of about 75K.PhDCondensed matter physicsUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159061/1/8225022.pd