LIBRATIONAL MOTION OF GUEST SPIN-PROBE MOLECULES IN GLASSY MEDIA

Echo-detected (ED) EPR spectra of nitroxide spin probes dissolved in g lassy materials evidence that guest molecules in these media undergo f ast librational motion. The mean square amplitude [alpha(2)] of this m otion can be simply derived from continuous wave (CW) EPR spectra by m easuring the field separation between the two outer spectral peaks. By comparing the ED and CW EPR data the correlation time tau(c) of libra tional motion could be evaluated. Above the glass transition temperatu re [alpha(2)] was found to increase sharply.