A RAMAN SPECTROSCOPY STUDY OF TAUTOMERIC O-HMIDLINE HORIZONTAL ELLIPSISO HYDROGEN BONDING

The work reports a study of the properties of tautomeric O-HMIDLINE HORIZONTAL ELLIPSISO hydrogen bonding (tau-bonding). The Raman spectra of crystalline and polycrystalline samples of terephthalic acid chains, benzoic acid dimers, and ibuprofen dimers are studied in the temperature region of 5-300 K. The protons on tau-bonds in terephthalic acid and ibuprofen are substituted by deuterium. Temperature dependences of the frequencies of tau-bond translational vibrations are analyzed, their relation to tunneling and proton hopping is discussed. It is shown that the propagation of the proton (deuteron) density distribution function into the neighboring empty potential well increases hydrogen bonding, while physical motion of the particle through the barrier or hopping over the barrier affect the omega(T) dependence of the vibration of the C=O bond in the tau-ring. On the example of ibuprofen, asymmetric tau-bonds are analyzed and the energy difference betweenL- andR-tautomers are measured.