PULSED NMR OF DILUTE ORTHO-H-2 IN SOLID NE, AR, KR, AND PARA-H-2

Pulsed NMR was used to study ortho-H2 as a dilute impurity in solid neon, argon, krypton, and para-H2. The nuclear relaxation arises principally from intramolecular spin-spin and spinrotation interactions. Many features of the observed relaxation are in excellent agreement with Fedders' predictions of the effects of local crystal fields. The H2 sites in solid neon and argon are found to have crystal fields with very low symmetry and the sites in p-H2 have fields with axial symmetry. The temperature variation of the rotational-quantum-state correlation frequencies of the o-H2 molecules is discussed in terms of a two-phonon Raman process. The data fit well the model of Van Kranendonk, but with an unusually low characteristic temperature near 40 K in all four host solids. In the rare-gas solids motional narrowings of intermolecular broadenings indicate that the coefficients of H2 impurity diffusion are similar to the coefficients of host self-diffusion. © 1979 The American Physical Society.