Short term proton spin conversion in solid CH4

Short term measurements were made of the static proton magnetic susceptibility of solid CH4 containing O2 impurities in the temperature range between 1.6 and 80 K. The samples were slowly crystallized and annealed above 80 K. A low level NMR Q-meter detector was used to measure the temperature dependence of the polarization of the hydrogen nuclei in methane relative to the polarization of fluorine nuclei in a thick teflon coil form surrounding the sample after thermal equilibration times of up to 2 h. The results can be consistently interpreted according to the James–Keenan model for Phase II of solid methane by assuming that, during a 2 h period, proton spin symmetry conversion essentially comes to equilibrium on the two disordered sublattices whose molecules are in states of nearly free rotation, but that conversion does not significantly occur within this time for molecules on the six remaining ordered sublattices.