Study of the Nuclear-Magnetic-Resonance Line Shape in hcpD2

A study of the nuclear-magnetic-resonance (NMR) absorption line shape in solid hcp ${\mathrm{D}}_2$ in the nondiffusive region is presented. The mole fraction $C$ of paramolecules (i. e., those with) a rotational angular momentum $J=1\mathrm{}$) ranged from 0.02 to 0.93, and the temperature was varied between 0.5 and 10 °K. Both continuous-wave (cw) and pulse (free-induction-decay) methods were used to obtain complementing information on the NMR absorption line shape. It is shown that the line shape attributed to $J=1\mathrm{}$ molecules broadens rapidly with decreasing temperature. At low enough temperatures, cw experiments record only the absorption from the $J=0\mathrm{}$ molecules. Second moments $M_2$ were obtained from the analysis of both cw and pulse experiments. Over a restricted range of molé fractions and temperatures, $M_2$ both for the signal from all the molecules and for that from the $J=0\mathrm{}$ molecules alone could be obtained separately from the free induction decay. The extrapolation of $M_2$ to the high-temperature limit where the line shape is determined by random intermolecular nuclear dipole-dipole interactions is in good agreement with theoretical predictions. A discussion is presented of the observed and theoretically expected temperature variation of $M_2$ for both $J=1\mathrm{}$ and $J=0\mathrm{}$ molecules. The results support the calculations by Harris which take account of admixtures of the $J=2\mathrm{}$ excited state in the $J=0\mathrm{}$ ground-state wave function, caused by the interactions with $J=1\mathrm{}$ molecules.