Localized Motion in Supercooled Glycerol as Measured by ² H-NMR Spin-Lattice Relaxation and Incoherent Neutron Scattering

Selectively deuterated glycerol has been subjected to 2 H-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 α-process the hydrogens perform a local motion (≈ 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.