Nuclear Magnetic Resonance of SolidifiedH2-D2Mixtures. I. Steady-State Experiments

Steady-state NMR measurements using a marginal oscillator technique at 10 Mc/sec have been made on solid mixtures of $n-{\mathrm{H}}_2-n-{\mathrm{D}}_2$ of $n-{\mathrm{H}}_2$ concentration from 100% to 1% in the temperature range 1.1°K to about 12°K. Striking differences in the line shape were observed, particularly in the $n-{\mathrm{D}}_2-\mathrm{rich}\mathrm{sample}$, with change in temperature, the line shape at the lowest temperatures revealing a composite structure. The question whether this line shape transition is due to isotopic phase separation is discussed, and this interpretation is considered unlikely. It is concluded that the transition is probably associated with a hindering of the rotation of the ortho-${\mathrm{H}}_2$ molecule. Narrowing of the resonance lines with increasing rf power was observed. It is shown that no satisfactory explanation of this effect is possible using the Bloch equations. This narrowing is in excellent agreement with a recent calculation by Provotorov, however, and his theory is used to obtain a value of the exchange interaction in solid ${\mathrm{H}}_2$ of approximately ${10}^{-7\mathrm{}}$ °K. The progressive-saturation technique is used to obtain values of the product $T_1{T}_2$ for several of the mixtures. The data showed that $T_1{T}_2$ has a value at 4.2°K of about 2×${10}^{-6\mathrm{}}$ ${\sec }^2$ for concentrations of $n-{\mathrm{H}}_2$ from 10% to 100%.