Nuclear magnetic spin relaxation in solid solutions of hydrogen bromide in deuterium bromide

Publisher Website
Google Scholar
Abstract
The following measurements have been made: the proton linewidth for HBr and 50% HBr/DBr in all solid phases by both steady state and Bloch decay methods, the deuteron spin-lattice relaxation time for DBr in the liquid and upper solid phase, the proton spin-lattice relaxation time for HBr and 50% HBr/DBr in the solid state at resonance frequencies of 215, 208, 143 and 90 MHz and the proton spin-lattice relaxation time in the rotating frame for radio-frequency fields of 145, 120 and 53 G. The measurements have been interpreted in terms of the various nuclear spin interactions and important information has been obtained about the molecular motion. The deuteron quadrupole coupling constant in DBr is estimated to be 250±50 kHz. It is found that for HBr in the upper temperature phase below the melting point the molecules are reorienting rapidly and diffusing slowly and the corresponding correlation times and diffusion constants are derived. On melting the reorientation rate hardly changes but the molecules become free to translate much more rapidly. It is possible that there is an observable spin-rotation contribution to spin-lattice relaxation in the upper solid phase in HBr. The relaxation in the lower temperature region of the upper phase has a strong contribution from proton-bromine dipolar relaxation of the second kind. A hysteresis effect similar to that observed in dielectric constant measurements is found around the lower of the upper pair of phase transitions in HBr. The relaxation in the middle phase is also controlled by proton-bromine interactions giving dipolar relaxation of the second kind but with the quantization of the bromine nucleus controlled by electric field gradients. The necessary theoretical analysis is given for relaxation with or without electric field gradient quantization for T1 and T1ρ. The linewidth in this phase shows motional narrowing of the second kind. The values of the molecular reorientational correlation time and the bromine nucleus spin-lattice relaxation times are predicted. The proton spin relaxation in the lowest temperature phase in HBr/DBr is closely related to the dielectric loss measurements. The interpretation is complicated by the strong bromine quadrupole interaction. `Vapour snakes' were observed during the solidification of HBr and DBr.