Bromine Nuclear Quadrupole Resonance in Ferroelectric Hydrogen Bromide

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Abstract
Bromine‐79 and bromine‐81 nuclear quadrupole resonance frequencies have been observed for HBr (below 70°K) and DBr (below 85°K). The observed frequencies decrease with temperature more rapidly than those calculated from the Bayer theory, and the lines broaden rapidly with increase in temperature above 45°K for HBr and above 65°K for DBr. The line broadening is interpreted as due to a 90° flip process of the molecules in the ferroelectric solid III. The correlation times and activation energy for this process are in good agreement with those calculated from dielectric dispersion data for DBr. The bromine‐79 resonance is 4 times broader in DBr than in HBr at low temperatures. A quantitive explanation of this effect has not been found. A doublet fine structure in the resonance of H79Br at low temperatures is interpreted as due to two kinds of chemically inequivalent molecules in the unit cell.