## Characterization and Assignment of Far Infrared Absorption Bands of K^{+} in Muscovite

M. Diaz^{1}, V.C. Farmer^{2} and R. Prost^{1}

^{1} Unité de Science du Sol, INRA, Route de Saint Cyr, 78026 Versailles, cedex, France

^{2} Soil Science Group, Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, UK

**Abstract:** To assign far infrared (FIR) absorption bands of K^{+} in muscovite, dichroic experiments were performed. For a muscovite crystal rotated about a crystallographic axis, *c**, *a*, or *b*, two bands corresponding to vibration modes of K^{+} appear, respectively, at 107 and 110 cm^{−1} (rotation about *c**), 107 and 143 cm^{−1} (rotation about *a*), and 110 and 143 cm^{−1} (rotation about *b*). Two in-plane modes at 107 and 110 cm^{−1} and one out-of-plane mode at 143 cm^{−1} are identified for the vibrations of K^{+} in muscovite. Each of these transition moments are near the crystallographic axes *b*, *a*, and *c*, respectively. These observations match well predictions based on the approximate C_{3i} symmetric environment of K^{+}, although the site symmetry in the space group of muscovite is only *C*_{2}.