Deuteron spectra, spin-lattice relaxation, and stimulated echoes in ice II.
(2)H NMR spectra, spin-lattice relaxation, and stimulated echoes have been measured in polycrystalline ice II in the temperature range of 84-145 K at ambient pressure. From the spectra we obtain the quadrupole coupling constant in ice II, e(2)qQ/h = (225.7+/-1.2) kHz, and the asymmetry parameter, eta = 0.118+/-0.006. At 145 K, a phase transition of ice II into ice I(c) is observed by a change of both, its spectral and relaxation behavior. The spin-lattice relaxation in ice II is bimodal, showing two components of approximately the same weight. The fast relaxing part of the recovery curve progresses monoexponentially and the temperature dependence of its mean relaxation time corresponds to an unusually low activation energy of 2.3 kJ mol(-1). The slowly relaxing part, displaying average relaxation times of about 4000 s, is significantly stretched with a Kohlrausch parameter of 0.6 and shows no temperature dependence. The stimulated echo experiments show a temperature independent correlation decay. The analysis of intermediate states indicates that no small-angle motions are involved in the underlying process. Both findings exclude an interpretation in terms of molecular motion. Instead, spin diffusion in the deuteron system has to be considered as the origin of the phenomena observed in the stimulated echo experiments.
Scheuermann
M
M
Institut fur Festkorperphysik, TU Darmstadt, Hochschulstr. 6, 64289 Darmstadt, Germany. marco.scheuermann@physik.tu-darmstadt.de
Geil
B
B
Löw
F
F
Fujara
F
F