Nuclear Magnetic Resonance Studies of Ammonium Halides. I. Proton Magnetic Resonance in Single Crystals of Ammonium Chloride and Ammonium Bromide

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Line shapes of proton magnetic resonance absorption in single crystals of ammonium chloride and bromide were measured in temperature range from 90°K to room temperature. At liquid air temperature, broad lines with structures corresponding to rigid configuration of ammonium ions were observed for both crystals. These structures were analysed by solving the nuclear magnetic energy levels of ammonium ion containing four protons and one nitrogen nucleus, and also by estimating the width of each component line. Theoretical line shapes coincide well with experimental ones in the chloride, but the agreement is worse in the bromide. Some possible origins for the disagreement in the latter case are discussed. Line width at higher temperatures narrowed by rapid rotation of ammonium ions was measured for various orientations of the crystal. A slightly discontinuous change of the second moments of the line was observed at the order-disorder transition point in the bromide.