Observation of spin conversion in solidCH313D by NMR

The temperature dependence of the proton magnetic susceptibility in ${}_{}{}^{13}{}_{}{}^{}\mathrm{CH}_3^{}{}_{}{}^{}$D has been measured throughout the temperature range from 1.6 to 95 K by cw NMR techniques. The observations were calibrated by an internal ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ spin thermometer. At 1.8 ± 0.3 K the mean-squared angular momentum of the protons $〈I(I+1\mathrm{})\mathrm{}〉$ was 2.71 ± 0.07. This value was significantly larger than the classical value of 2.250, due to nuclear spin conversion. At 11.4 K the conversion time constant was estimated to be ∼ 30 h.