Libration of the OH— Ion in LiOH
1965; American Institute of Physics; Volume: 43; Issue: 3 Linguagem: Inglês
10.1063/1.1696851
ISSN1520-9032
Autores Tópico(s)Luminescence Properties of Advanced Materials
ResumoMuch discussion and controversy has taken place in recent years on libration of the OH− ion in hydroxide crystals. Recent work on the charge distribution in the OH− ion makes it feasible to calculate the librational frequency and amplitude in LiOH arising from thermal agitation. A simplified model of the libration is chosen which corresponds with the Einstein model for this mode. The calculation is based on the change in lattice energy with rotation of a single OH− ion, involving Madelung, van der Waals, and repulsive terms. The results indicate considerable anisotropy of libration at thermal amplitudes at room temperature. The calculated frequency thus varies with direction so that ν̃a=342 cm−1 while 〈ν̃〉Av=396 cm−1. At room temperature the calculated rms thermal displacements of the hydrogen atom arising from libration agree well with those derived from the results of neutron-diffraction experiments. The apparent success of this simple model in LiOH suggests that it might be extended to similar layer-lattice hydroxide crystals.
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