Nuclear Magnetic Resonance of the Solid Phases of HCl, HBr, and HI

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Abstract
Proton relaxation times, second moments, and deuteron line splittings have been measured in the solid phases of HCl, HBr, and HI from 50° to 200°K. In solid I of each hydrogen halide two types of molecular motion have been detected: (1) a rapid rotational reorientation and (2) translational diffusion of the molecules. Solid III of HBr shows an intermediate plateau in the proton second moment and both HBr and HI have a well-defined minimum in the rotating-frame relaxation time T1ρ. These effects are interpreted as due to a single-plane reorientation process. Similar minima of T1ρ are observed in solid II of HI and the intermediate solid of HBr, which are ascribed to two-plane and three-plane reorientation processes. The splitting of the deuteron resonance of DBr and DI is quite dependent on temperature but not as strongly dependent as expected for equal site occupational probability. It is proposed that in the ferroelectric solid II of HCl the molecules undergo a single-plane reorientation process but with nonequal orientational site probabilities. Correlation times for these motions are compared with correlation times derived from dielectric loss measurements. The two sets of correlation time data are generally in order-of-magnitude agreement.