On the rotational motion of the ammonium ion in the CsCl-type phase of NH4Br: Results from quasielastic neutron scattering
- 14 July 1980
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 73 (2) , 934-939
- https://doi.org/10.1063/1.440212
Abstract
The rotational motion of the ammonium ion in polycrystalline NH4Br has been investigated by quasielastic incoherent neutron scattering at 12 different temperatures between 297 and 409 K. The measured spectra were corrected for multiple scattering and compared to the C4‐rotational jump model. The elastic incoherent structure factor was determined experimentally within the range 0.15⩽Q⩽1.72 Å−1 of elastic wave vector transfer. It yields a N‐H bond length of 1.028±0.005 Å. The rotational jump rate was found to follow an Arrhenius law, 1 τC4[s−1] ±0.16)×1013 exp{(−1623±16)/T[K]}, with an activation energy of Ea=13.49±0.13 kJ/mole. Within the studied temperature interval the mean square hydrogen vibration amplitude can be described by the expression 〈u2〉 [Å2−]±1.6)×10−4 T[K] −(16.4±6)×10−2.Keywords
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