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Bifurcated hydrogen bonds in water
Author(s) -
Giguère Paul A.
Publication year - 1984
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250150513
Subject(s) - hydrogen bond , molecule , fermi resonance , raman spectroscopy , chemistry , liquid water , spectral line , hydrogen , crystallography , infrared spectroscopy , tetrahedron , thermodynamics , physics , organic chemistry , astronomy , optics
A new model is proposed for liquid water, based on recent studies of the Raman spectra as a function of temperature. It features two kinds of hydrogen bonds: in addition to the well known linear hydrogen bonds (LHB), predominant in cold water, there are some bifurcated hydrogen bonds (BHB) between three water molecules. These three‐centered bonds, mainly electrostatic, have an average energy of 2.5 kcal mol −1 , about half of that of the LHB. Their characteristic OH stretching frequency is around 3420–3440 cm −1 , compared with 3220 cm −1 for the LHB. In addition, there are a few percent of nearly free OH groups, i.e. non‐hydrogen‐bonded (NHB), with a stretching frequeney of ca 3615 cm −1 . Reorientation between these three states occurs through rotation of the H 2 O molecules about one of their OH bonds. Thus, on melting, one third of the hydrogen atoms move out of the tetrahedral framework to occupy interstitial sites in the open ‘shafts’ characteristic of the ice structure. As in the case of ice, Fermi resonance between the ν 1 and 2 ν 2 levels has little impact on the vibrational spectra of liquid water and iee. The hybrid molecule, HDO, does not form LHB with H 2 O or D 2 O, hence its simpler spectra. The BHB model can account much better than previous models for the thermodynamic anomalies of water.