H-2-NMR-STIMULATED ECHO STUDY OF ULTRASLOW REORIENTATIONAL MOTION IN VISCOUS GLYCEROL NEAR ITS GLASS-TRANSITION TEMPERATURE

2H-NMR stimulated echo experiments have been performed in order to study the molecular basis of the a-process in viscous glycerol near its glass transition temperature. Decay functions following modified Jeener-Broekaert pulse sequences were compared with predictions from different models for molecular reorientation. Rotational diffusion, rotational random jumps, rotational fixed-angle jumps and combinations of diffusive and jump motions have been tested. All data are fitted with a log-Gaussian distribution of correlation times. Thereby, small- but finite-angle reorientation processes turn out to dominate in the 103s… 10°s regime. Pure large-angle rotational jumps can be ruled out with high significance. The mean rotational correlation time, (rc>, agrees with results from other relaxation experiments which monitor the a-process of the glass transition. © 1990 IOP Publishing Ltd.