LOCALIZED MOTION IN SUPERCOOLED GLYCEROL AS MEASURED BY H-2-NMR SPIN-LATTICE RELAXATION AND INCOHERENT NEUTRON-SCATTERING

Selectively deuterated glycerol has been subjected to H-2-NMR spin-lattice relaxation and quasi-elastic neutron scattering experiments. The measurements yield relaxation rates and a non-Gaussian Q-dependence of the Debye-Waller factor which are different for the two hydrogen sites. The data analysis shows that below the onset of the glass transition alpha-process the hydrogens perform a local motion (almost-equal-to 10(-12)s) in addition to what is expected from harmonic phonons. The resulting mean-square displacements are highly temperature dependent but are significantly smaller than those found in van der Waals glasses. Amplitudes and activation energies of the carbon-bonded and oxygen-bonded hydrogens are different. A possible mechanism is discussed.