REINVESTIGATION OF THE WATER BENDING REGION IN THE SPECTRA OF GYPSUM-LIKE COMPOUNDS - AN FTIR STUDY

The IR spectra of gypsum (CaSO4.2H(2)O) and the related CaSeO4.2H(2)O and YPO4.2H(2)O have been reinvestigated by FTIR spectroscopy. For the components of the correlation-field doublet in the delta(HOH) region, the measured ratio of the intensities for CaSO4.2H(2)O is rather clos e to that derived (employing the oriented-gas model) from neutron diff raction data. From the acquired spectroscopic data for the selenate an d the phosphate (no neutron data are available for either of them), th e angle between the HOH bisector and the C-2 axis was estimated. The s mall but significant increase in the frequency separation of the compo nents of the delta(HOH) doublet on lowering the temperature can be exp lained in terms of the unit cell contraction which brings the water mo lecules closer to each other and thus increases the dipole-dipole inte ractions which are believed to be the principal cause for the correlat ion-field splitting. (C) 1997 Elsevier Science B.V.