Abstract
Abstract The short-time rotational dynamics of nearly spherical and cylindrical spin probes in supercooled and glassy o-terphenyl is investigated by nonlinear electron spin resonance spectroscopy. At higher temperatures, the relaxation is exponential and the Debye-Stokes-Einstein law holds, τ α(η/T). τ is the rotational correlalion time, η the shear viscosity and T the temperature. On cooling, the coupling of the short-time rotational dynamics and the shear viscosity weakens, and a fractional Debye-Stokes-Einstein law τ α(η/T)ξ, with ξ constant, is observed. At the lower temperatures, the rotation is activated. A scaling of the short-time rotational dynamics of the different molecular probes is obtained for the overall range of temperature.
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