Positive temperature coefficient of the iodine quadrupole resonance frequency in ammonium tri-iodide due to reorientation of the ammonium ion
- 1 January 1983
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 79 (4) , 497-504
- https://doi.org/10.1039/f29837900497
Abstract
A large increase in the nuclear quadrupole resonance (n.q.r.) frequency of a terminal iodine atom Ia of the I3 anion in NH4I3 in NH4I3 is explained by a simple theory which relates the reorientation of the ammonium ion to a concerted change in the relative weights of the resonance structures of the I3 anion through formation and scission of the N—H Ia hydrogen bond. The weight of the structure (I– a I—I) oscillates between 0.75 (hydrogen-bonded) and 0.48 (non-bonded) as the NH4 cation is reoriented. The proton spin–lattice relaxation time was measured between 77 and 240 K; a minimum of 2.45 ms occurs at 80 K. The activation energy for ammonium reorientation is 7.53 kJ mol–1. The energy of a hydrogen bond, including the effect of the change in relative weights of I3, was derived as 5.20 kJ mol–1.Keywords
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