Spin-Gitter-Relaxation der Protonen in hexagonalem Eis

Abstract

Proton spin-lattice relaxation timesT₁ in hexagonal ice have been measured from −10 to −80°C for different external Zeeman fieldsH_R from 0.125 to 6.57 kOe. The results can be described byT₁∼H ² _R exp(ΔE_c/kT) (ΔE_c=activation energy). In pure ice (H_R ∥c-axis)ΔE_c is 0.62 eV, whereas relaxation due to impurities givesΔE′_c≈0.25 eV. The analysis of these results including additional data of the dielectric relaxation and the self-diffusion coefficient yields thatT₁ in pure ice is determined mainly by the motion of Schottky defects. Bjerrum faults give an additional but small contribution. SettingT₁=C·τ_c (τ_c=molecular correlation time which is proportional to exp(ΔE_c/kT), C=constant depending onH_R and molecular distances) we calculatedC with the model mentioned above and found e.g. 0.88 · 10⁶ atH_R=6.57 kOe.E′_c≈0.25 eV is assumed to be the energy of migration of Bjerrum and ionic faults.