Datensatz

Zusammenfassung

Nuclear relaxation in the rotating frame was measured to investigate slow but large amplitude mobility in naphthalene- and biphenyl-type crystals. Reorientation of the whole molecule around molecular axes appears to be the most probable motion. While increasing fluorine substitution slows down the mobility in biphenyl the opposite is true for naphthalene crystals. According to the effective external fields acting on the sample the following relaxation rates were measured: : relaxation of Zeeman order in the high magnetic field H0; : relaxation of Zeeman order in the rotating frame effective field Hϱ under rf-irradiation; : relaxation of dipolar order in the local dipolar field : spin-spin relaxation rate. For the dipolar relaxation rate in some crystals deviations by orders of magnitude were found with respect to the following theoretical predictions: (1) All relaxation rates are expected to be essentially equal in the “extreme narrowing” regime: ω0τ r ⪡ 1. (2) The ratio of the relaxation maxima , should be given approximately by that of the inverse Larmor frequencies in the effective field .