Rotational ordering and nuclear spin-lattice relaxation in solid methane

Abstract

The proton spin-lattice relaxation time has been measured in solid CH4 down to 0.4 K. In the ordered phase at 9 < T < 20 K the relaxation process is induced by librons. The energy of the librons (~75 K) is in excellent agreement with the theoretical prediction by Yamamoto, Kataoka, and Okada. T1 has been found constant within experimental error between 0.4 and 9 K. The mechanism responsible for relaxation in this lower temperature region is attributed to the adiabatic molecular reorientation of the ordered T molecules. The cooling procedure has been found in special cases to affect the experimental results.