Characterization and assignment of far infrared absorption bands of K+ in muscovite

To assign far infrared (FIR) absorption bands of K+ in muscovite, dichroic experiments were performed. For a muscovite crystal rotated about a crystal lographic 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 c m(-1) are identified for the vibrations of K+ in muscovite. Each of these t ransition moments are near the crystallographic axes b, a, and c, respectiv ely. These observations match well predictions based on the approximate C-3 i symmetric environment of K+, although the site symmetry in the space grou p of muscovite is only C-2.