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In aqueous acetone solutions, the strong bathochromic shifts observed on the OH and CO stretch infrared (IR) bands are due to hydrogen bonds between these groups. These shifts were evaluated by factor analysis (FA) that separated the band components from which five water and five acetone principal factors were retrieved [J. Chem. Phys. 119, 5632 (2003)]. However, these factors were abstract making them difficult to interpret. To render them real an organization model of molecules is here developed whose abundances are compared to the experimental ones. The model considers that the molecules are randomly organized limited by the hydrogen bond network formed between the water hydrogen atoms and the acetone or water oxygen atoms, indifferently. Because the oxygen of water has two covalent hydrogen atoms which are hydrogen-bonded and may receive up to two hydrogen atoms from neighbor molecules hydrogen-bonded to it, three types of water molecules are found: OH[sub 2], OH[sub 3], and OH[sub 4] (covalent and hydrogen bonds). In the OH stretch region these molecules generate three absorption regimes composed of ν[sub 3], ν[sub 1], and their satellites. The strength of the H-bond given increases with the number of H-bonds accepted by the oxygen atom of the water H-bond donor, producing nine water situations. Since FA cannot separate those species that evolve concomitantly the nine water situations are regrouped into five factors, the abundance of which compared exactly to that retrieved by FA. From the factors’ real spectra the OH stretch absorption are simulated to, respectively, give for the ν[sub 3] and ν[sub 1] components the mean values for OH[sub 2], 3608, 3508; OH[sub 3], 3473, 3282 and OH[sub 4], 3391, 3223 cm-1. The mean separations from the gas-phase position which are respectively about 150, 330, and 400 cm-1 are related to the vacancy of the oxygen electron doublets: two, one, and zero, respectively. No acetone hydrate that sequesters water molecules is formed. Similarly, acetone produces ten species, two of which evolve concomitantly. Spectral similarities further reduce these to five principal IR factors, the abundance of which compared adequately to the experimental results obtained from FA. The band assignment of the five-acetone spectra is given. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The crystal structures of 6-methyl-2-ethyl-3-hydroxypyridiniun nitrate (C8H12NO)NO3 (I) and fumarate (C8H12NO)2C4H2O4 (II) were solved and refined from X-ray single crystal diffraction data (CuKα, (I) a=4.6477(2), b=14.5906(9), c=14.5551(8) Å, β=99.100(4)°, space group P21/c, Z=4, Rp/Rwp=0.033/0.047; (II) a=8.8293(3), b=13.4268(5), c=8.3893(3) Å, β=96.303(3)°, space group P21/c, Z=2, Rp/Rwp= 0.034/0.049). Both structures are built of infinite chains along ac diagonal of the unit cells formed by hydrogen bonding between the hydroxypyridium cation and the corresponding anion. Each fumarate anion is linked to four hydroxypyridium cations while nitrate anion is connected with two hydroxypyridium cations only leaving one oxygen atom in the nitrogen group isolated. [ABSTRACT FROM AUTHOR]

As a result of the experimental study of water Raman spectra and water-ethanol solutions, it was established that Fermi resonance and Darling-Dennison resonance make significant contribution to the formation of Raman spectra. Basing on the analysis of the spectra using optimization algorithms, the coupling constants W and the contributions of Fermi resonance to spectra in water and aqueous ethanol solutions at various temperatures were calculated. The contribution of the resonance of Darling-Dennison to the formation of the spectra of solutions was analyzed. It was established that Fermi and Darling-Dennison resonances manifested stronger in a 20% solution of ethanol in water in comparison with pure water. These resonances weakened with increasing temperature. This effect was explained from the point of view of strength of hydrogen bonds. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Direct measurements of the individual dynamics of water in bulk and ionic hydration shells in aqueous ionic solutions are quite experimentally challenging because the different subsets of water in bulk and ionic hydration shells are not spectrally well-resolved in most aqueous ionic solutions. In contrast, the different subsets of water in the bulk, cationic hydration shell, and anionic hydration shell in aqueous NaPF6 solutions were found to be spectrally well distinct. Such spectral features allowed us to study the individual dynamics of the different subsets of water in aqueous NaPF6 solutions. In this work, we studied the hydrogen-bond (H-bond) structure and dynamics of water in aqueous NaPF6 solutions at different NaPF6 concentrations by FTIR, Raman, and IR pump–probe spectroscopy. Three different subsets of water in the bulk, cationic hydration shell, and anionic hydration shell were found to have their own characteristic hydroxyl stretch peaks (eigen spectra) in FTIR and Raman spectra and have unique vibrational lifetimes independent of NaPF6 concentration. However, the orientational relaxation dynamics, r(t), were not able to be separately measured for three different subsets of water. The overall orientational relaxation times were found to be linearly dependent on the solution viscosity and were reasonably well described by the Debye–Stokes–Einstein equation. Finally, the frequency-dependent transition dipole moments of the hydroxyl (–OD) stretch vibration obtained in neat water and aqueous 3.0 M NaPF6 solution were compared and found to be dependent on the nature of H-bonds. [ABSTRACT FROM AUTHOR]

A general case of interaction between two oscillators of statistically distributed frequencies has been studied. The interaction between fundamental and overtone vibrations (Fermi resonance) can be a special case. The feasible, non-zero original intensity of an overtone is also considered. Frequency distributions can be any (e.g., Gaussian, Lorentzian, and a Dirac delta function). The analytical expressions are derived for band shapes in the infra-red spectra. However, the formalism developed is also applicable to calculations of the isotropic and anisotropic components of Raman spectra. The formulas have allowed us to describe the infrared spectra of several 1:1 complexes of amines with the bases available from the literature, where Fermi-doublet bands are broadened due to hydrogen bonding. It is shown that the traditional description of Fermi resonance considering only the peak frequencies and intensities of the decomposed experimental spectral contours (ignoring their form), provides incorrect results. [ABSTRACT FROM PUBLISHER]

5,6-Dihydrothymine (DHT) is a nucleobase lesion induced by the action of ionizing radiation on thymine residue in DNA. In this work, we present the hydrogen bonding base pairs involving 5,6-dihydrothymine bound to four bases in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). Full geometry optimizations are performed for the studied complexes by the B3LYP method. Interaction energies are corrected for the basis set superposition error, using the full Boys-Bernardi counterpoise correction scheme. Hydrogen bonding patterns of these base pairs are characterized using NBO and AIM analysis. According to the calculated binding energies and structural parameters, the stability of the base pairs decrease in the following order: DHT:G ∼ DHT:A > DHT:C > DHT:T. [ABSTRACT FROM AUTHOR]

Vibrational spectra of the isolated complementary guanine-cytosine pair are calculated at the B3LYP/6-311++G( d,p) level. The hydrogen bond effect on the structure, frequency positions, and intensities of normal vibrations of the pair are analyzed in comparison with the spectra of isolated guanine and cytosine molecules. Characteristic spectral features of the formation of the complementary guanine-cytosine base pair are revealed. [ABSTRACT FROM AUTHOR]

Excess thermodynamic functions of D2O water have been calculated from the vibrationally decoupled O−D stretching spectra of very dilute solutions of HOD in H2O. Comparison of the results with reference calorimetric data for water showed a good correspondence for excess heat capacity above the melting point of ice. The excess enthalpy at the melting point also coincides well with latent heat of melting. [ABSTRACT FROM AUTHOR]

Statistical distributions of the frequencies of OH vibrations calculated from the experimental Raman spectra of HOD molecules over the temperature range of 10-200 °C using the recently developed deconvolution technique have been analysed in the framework of fluctuation theory of hydrogen bonding. Two temperature independent functions that are the basis of the Zhukovsky theory for describing the temperature transformation of frequency distribution functions of OH vibrations in a statistical ensemble of O-H···O bonds were established and analytically approximated. This made it possible to reconstruct the entire set of initial spectra and to extrapolate their forms to a wider temperature range. These results support the continuum model of liquid water structure. [ABSTRACT FROM AUTHOR]

We calculated the proton kinetic energies Ke(H) of ice under high pressures up to 63 GPa by assuming the harmonic approximation. The input measured optical frequencies of vibration, libration, and translation of ice VII versus pressure as well as the H2O geometry and the distances ROH necessary for calculating Ke(H) (at 298 K) were taken from the literature. The resulting Ke(H) values were found to decrease gradually with increasing pressure, approaching the region where the H-atom is symmetrically hydrogen bonded between two oxygens in the OH-O system. Interestingly, the Ke(H) results were found to be consistent with those of other materials such as Rb3H(PO4)2 and KH2PO4 having similar ROH and ROO distances in the OH-O system. Similar calculations were also carried out for D2O. [ABSTRACT FROM AUTHOR]