Interpretation of¹H NMR results of HD impurities in solid H₂. I. Spin-spin relaxation

Abstract

Previous¹H NMR results on HD impurities in solid H₂ samples of low ortho concentration (X≲0.01) are reexamined, resulting in a different interpretation of the spin-spin relaxation timeT ₂. The relaxation time is found to be measured by using short rf pulses rather than the long (100–120 µsec) pulses used previously for the spin-echo pulse sequences. This is due to the fact that the nuclear spin dipolar flip-flop interactions between the HD and ortho-H₂ molecules are effectively quenched because of the large intramolecular dipolar splittings of the H₂ molecules. The measured spin-spin relaxation times for the HD impurities in a sample ofX≲0.01 are found to be consistent with those from statistical theory, revealing no appreciable motional narrowing, which was invoked previously.