Nuclear Magnetic Resonance in Solid Hydrogen

The fine structure of the nuclear magnetic resonance line in solid hydrogen at low temperatures (1.15°K) was studied experimentally using a recording meter technique. The observed line shape can be explained quantitatively by the magnetic dipole interaction of the two protons in a hydrogen molecule, provided one takes into consideration the effect of the crystalline potential responsible for lifting the rotational degeneracy of the ortho-molecules in the solid. Extremely general assumptions concerning the nature of this crystalline potential are sufficient to account for the nuclear resonance data; in particular, one can treat the case where this potential, by virtue of the random mixture of ortho- and para-molecules in the solid, is not symmetric and not the same at the positions of different ortho-molecules. An apparent hysteresis effect in solid hydrogen was observed and some experiments were also performed on solid HD and ${\mathrm{D}}_2$. The general theory developed in connection with the foregoing experiments also predicts the detectability in solid hydrogen of a resonance line in zero external magnetic field, this line constituting a direct measure of the dipole interaction responsible for the fine structure of the resonance line in high fields. Despite experimental difficulties peculiar to the zero-field experiment, this resonance line was found at the expected frequency of about 165 kc/sec.