Temperature-dependent Raman study of ammonium perchlorate single crystals: Evidence for NH4+ quantum rotation below 30 K.

Abstract

We report a detailed temperature-dependent Raman study of oriented single crystals of ${\mathrm{NH}}_{4}$${\mathrm{ClO}}_{4}$ and ${\mathrm{ND}}_{4}$${\mathrm{ClO}}_{4}$ in the lattice-mode region from 10 to 300 K. Based on the deuterium shift, characteristic changes in bandwidth with temperature, structural information, etc., we have assigned the Raman bands in the lattice-mode region, which provides deeper insight into the dynamics of ammonium ions in the lattice. We have observed temperature-dependent sidebands by \ifmmode\pm\else\textpm\fi{}19 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (10 K) from the main bands associated with some of the internal and lattice modes of the ${\mathrm{NH}}_{4}^{+}$ ion below 30 K. These spectral features have been explained in terms of a model in which the ${\mathrm{NH}}_{4}^{+}$ ion rotates almost freely about one of the axes coinciding with the N-H(2)...O(1) bond while it performs librational motion about the two perpendicular axes below 30 K.