L. Andreozzi et al., JUMP REORIENTATION OF A MOLECULAR PROBE IN THE GLASS-TRANSITION REGION OF O-TERPHENYL, Journal of physics. Condensed matter, 8(21), 1996, pp. 3795-3809
The reorientation process of a molecular probe dissolved in the fragil
e glass former o-terphenyl is studied via electron spin-resonance spec
troscopy. Owing to the good resolution of the ESR lineshape in the so-
called slow-motion regime, we are able to discriminate between diffusi
ve and jump rotations. In the region of the glass transition (T-g - 31
K < T ( T-g + 17 K) the results are at variance with the diffusion mo
dels and are fairly well reproduced by assuming that the probe jumps w
ith steps phi = 80 degrees(-5 degrees)(+10 degrees). The temperature d
ependence of the correlation time is well described, in the temperatur
e range investigated, by a double Arrhenius law broken at T-g. The fin
dings are compared with previous NMR, dielectric, fluorescence and mol
ecular dynamics studies.