Nonharmonic transverse vibration of the H-bonded molecules and the THz spectra in ice and water
ABSTRACT A nonlinear equation of motion is found for the dimer comprising two charged H2O molecules. The THz dielectric response to nonharmonic vibration of a nonrigid dipole, forming the hydrogen bond (HB), is found in the direction transverse to this bond. An explicit expression is derived for the autocorrelator that governs the spectrum generated by transverse vibration (TV) of such a dipole. This expression is obtained by analytical solution of the truncated set of recurrence equations. The far infrared (FIR) spectra of ice at the temperature −7 °C are calculated. The wideband, in the wavenumber (frequency) ν range 0…1000 cm−1, spectra are obtained for liquid water at room temperature and for supercooled water at −5.6 °C. All spectra are represented in terms of the complex permittivity ε(ν) and the absorption coefficient α(ν).The obtained analytical formula for ε comprises the term ε⊥ pertinent to the studied TV mechanism with three additional terms Δεq, Δεμ, and εor arising, respectively, from: elastic harmonic vibration of charged molecules along the H-bond; elastic reorientation of HB permanent dipoles; and rather free libration of permanent dipoles in ‘defects’ of water/ice structure.The suggested TV-dielectric relaxation mechanism allows us: (a) to remove the THz ‘deficit’ of loss ε″ inherent in previous theoretical studies; (b) to explain the THz loss and absorption spectra in supercooled (SC) water; and (c) to describe, in agreement with the experiment, the low- and high-frequency tails of the two bands of ice H2O located in the range 10…300 cm−1. Specific THz dielectric properties of SC water are ascribed to association of water molecules, revealed in our study by transverse vibration of HB charged molecules.
- Angewandte Chemie 01/2009; 121(17):3230-3233.
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ABSTRACT: Similarities and differences: Far-infrared spectra of protic ionic liquids could be assigned to intermolecular bending and stretching modes of hydrogen bonds. The characteristics of the low-frequency spectra resemble those of water. Both liquids form three-dimensional network structures, but only water is capable of building tetrahedral configurations. EAN: ethylammonium nitrate, PAN: propylammonium nitrate, DMAN: dimethylammonium nitrate.Angewandte Chemie International Edition 04/2009; 48(17):3184-6. · 11.34 Impact Factor
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ABSTRACT: A two-fraction model that makes it possible to calculate analytically the complex dielectric permittivity of ice in the far infrared and submillimeter wavelength ranges is proposed. The librational and vibrational fractions are considered. The first fraction, consisting of rigid dipoles executing anharmonic reorientations in defects of the structure, gives rise to the librational band of ice at 800 cm−1. The second fraction consists of elastically vibrating oppositely charged H-bonded molecules. This fraction describes two bands of ice in the range 100–300 cm−1, and the nonresonant background of dielectric losses in the submillimeter wavelength range. The dielectric permittivity spectra of ice calculated for the temperature of −7°C are consistent with the experimental spectra. The spectra of ice at the temperature −30°C are predicted.Optics and Spectroscopy 01/2006; 101(5):698-707. · 0.56 Impact Factor