Pulsed NMR studies in solid H2. III. Spin-lattice relaxation times
Abstract
We report a systematic study of the longitudinal relaxation time T1 for solid H2 samples with ortho concentration X between 0.15 and 0.70 and for 0.1≲T≲2 K. It is over this temperature region that substantial orientational ordering takes place, which drastically affects T1. The measurements were made using the solid echo technique at 9 and 27 MHz. By Fourier-transforming the echo decay, it was possible to investigate the recovery from saturation of the various parts of the NMR absorption line as a function of their distance ν-νLfrom the center at the Larmor frequency νL.The dependence of T1 on ν-νLis particularly noticeable in the hcp disordered (para-orientational) phase at the lowest temperatures, where the NMR absorption is broad, and this observation is qualitatively explained. An attempt is made to understand the general features of T1 in the cubic ordered phase and in the hcp para-orientational phase in terms of certain relaxation mechanisms. A comparison with previous work is presented. © 1983 Plenum Publishing Corporation.