THE INFRARED SPECTRUM OF THIS AMMONIUM ION IN LATTICES OF THE NaCl TYPE
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Date
1959
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Ohio State University
Abstract
At the temperature of liquid helium no less than 14 lines appear within $25 cm^{-1}$ of the sharp central peak of the bending mode of $NH_{4}^{+}$ ions in dilute solid solution in alkali halide lattices of the NaCl typo. These solutions contain the $NH_{4}^{+}$ ions in an environment closely related to that in the pure ammonium halides in the high temperature NaCl type phase. On the basis of infrared and Raman Spectra, as well as neutron diffraction, it has been concluded previously that the stable structure in these phases is one in which one proton is bound in a N-H... X bond and the ion rotates about this axis. It has not been found possible thus far to interpret the observed fine structure in these terms. Consideration of the electrostatic potential of a tetrahedron in an octahedral field indicates the presence of 144 identical minima. This suggests the possibility of nearly free rotation. But, although this conclusion is supported by heat capacity measurements the present infrared spectra do not appear to be those of a slightly perturbed spherical top. The spectrum will be presented together with a theoretical discussion.
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Author Institution: Department of Chemistry, Princeton University