Normal coordinate analysis of the orthorhombic trifluorides MF3 (M ¼ Gd, Tb, Er, Yb)

A short-range force constant model has been applied for the first time to investigate the phonons in trifluorides MF3 (M ¼ Gd,Tb,Er,Yb) in their orthorhombic phase. The normal symmetry coordinates for the orthorhombic trifluorides have been computed. The calculations with 14 stretching and bending force constants provide good agreement for the observed Raman frequencies. The infrared frequencies have been assigned. q 2004 Elsevier B.V. All rights reserved.