A detailed analysis of the temperature evolution of polarized and depolarized Raman spectra in the OH stretching region of pure liquid alcohols has been performed in order to gain more insights on the nature of the noncoincidence effect (NCE) in inhomogeneously broadened OH profiles. For 1-octanol temperature-induced difference spectra, wavenumber-dependent depolarization ratios and H-bond energy dispersion have been evaluated. The results allow for a consistent interpretation of the overall NCE in terms of distinct spectral components. In practice, it results that different classes of oscillators can be singularly characterized by specific NCEs. The major contribution to the overall NCE is experimentally separated and arises from OH oscillators embedded within the H-bonded chain structures characterized by an average H-bonding enthalpy of ca 20 kJ/mol. The study has been extended to Raman OH profiles of liquid ethanol, 2-octanol and tert-butanol to understand the effects of the hydrophilic and hydrophobic molecular moieties in determining the strength on the vibrational coupling, responsible for the resonant transfer of vibrational energy (RET), in these liquid systems. Copyright (c) 2005 John Wiley & Sons, Ltd.
Raman non-coincidence effect on OH stretching profiles in liquid alcohols
PAOLANTONI, Marco;SASSI, Paola;MORRESI, Assunta;
2006
Abstract
A detailed analysis of the temperature evolution of polarized and depolarized Raman spectra in the OH stretching region of pure liquid alcohols has been performed in order to gain more insights on the nature of the noncoincidence effect (NCE) in inhomogeneously broadened OH profiles. For 1-octanol temperature-induced difference spectra, wavenumber-dependent depolarization ratios and H-bond energy dispersion have been evaluated. The results allow for a consistent interpretation of the overall NCE in terms of distinct spectral components. In practice, it results that different classes of oscillators can be singularly characterized by specific NCEs. The major contribution to the overall NCE is experimentally separated and arises from OH oscillators embedded within the H-bonded chain structures characterized by an average H-bonding enthalpy of ca 20 kJ/mol. The study has been extended to Raman OH profiles of liquid ethanol, 2-octanol and tert-butanol to understand the effects of the hydrophilic and hydrophobic molecular moieties in determining the strength on the vibrational coupling, responsible for the resonant transfer of vibrational energy (RET), in these liquid systems. Copyright (c) 2005 John Wiley & Sons, Ltd.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
