Asymmetry Parameters and the Temperature Dependence of the PQR Frequencies of 127I in SnI4

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Abstract
The pure quadrupole resonance spectrum of 127I in solid SnI4 has been measured from 4.2°–300°K at atmospheric pressure. The data have been fitted with a form of Bayer–Kushida theory which incorporates temperature effects due to field‐gradient asymmetry. The adjustable parameters were determined for a given temperature range by a procedure designed to yield as nearly as possible both the best fits to the data and the same value for a given parameter for both the high‐ and low‐frequency curves at a given lattice site. This procedure was largely successful and resulted in values for the asymmetry parameter, viz., 0.012 and zero for the two inequivalent iodine sites, which appear almost independent of the temperature range selected. The results for the average normal‐mode lattice frequency may be taken to indicate that several of the low‐frequency vibrational modes of the SnI4 molecule contribute importantly to the temperature dependence of the quadrupole resonance frequency in the solid.