Vibrational spectra of water molecules in some transition metal dichloride dihydrates

Abstract

The i.r. spectra of MCl 2.2H 2O ( M = Co, Fe, Mn) and partially and almost completely deuterated derivatives thereof were recorded at liquid nitrogen and room temperature in a low wavenumber region covering 700-200 cm −1. Librational bands were assigned unambiguously to rocking and wagging modes by taking advantage of a theoretical conclusion that the isotopic frequency ratio, v H 2O v HDO (but not v H 2O v D 2O , is considerably different between the rocking mode and the wagging mode. The force constant of rocking is one order of magnitude greater than that of wagging. The result is explained by means of a simple point-charge model.