Infrared studies of water in crystalline hydrates: gypsum, CaSO 4 •2H 2 O
1969; NRC Research Press; Volume: 47; Issue: 8 Linguagem: Inglês
10.1139/v69-223
ISSN1480-3291
AutoresVera Seidl, Osvald Knop, Michael Falk,
Tópico(s)Spectroscopy and Quantum Chemical Studies
ResumoInfrared spectra of partially deuterated hydrates yield the fundamental frequencies of isotopically dilute H 2 O, D 2 O, and HDO molecules. Isotopic dilution eliminates vibrational coupling and allows the determination of the total number of crystallographically distinct water molecules in the crystal. It also yields the number of distinct symmetric (C 2v ) and asymmetric (C s ) water molecules. The results for gypsum show that all the water molecules are equivalent and that they are asymmetric, in agreement with crystallographic results. The extent of asymmetry is measured by the difference between the two OH stretching frequencies of HDO molecules, which is 90 cm −1 . This corresponds to an estimated difference of 0.02 Å in the [Formula: see text] distances of the two hydrogen bonds. The spectra of partially deuterated gypsum show clearly that spectral features previously explained by the presence of two sets of distinct water molecules or by proton tunnelling, are in fact due to vibrational coupling.
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