  Using depolarized light scattering, we have recently shown that structural
relaxation in a broad range of supercooled liquids follows, to good
approximation, a generic line shape with high-frequency power law
$\omega^{-1/2}$. We now continue this study by investigating a systematic
series of polyalcohols (PAs), frequently used as model systems in
glass-science, i.a., because the width of their respective dielectric loss
spectra varies strongly along the series. Our results reveal that the
microscopic origin of the observed relaxation behavior varies significantly
between different PAs: While short-chained PAs like glycerol rotate as more or
less rigid entities and their light scattering spectra follow the generic
shape, long-chained PAs like sorbitol display pronounced intramolecular dynamic
contributions on the time scale of structural relaxation, leading to systematic
deviations from the generic shape. Based on these findings we discuss an
important limitation for observing the generic shape in a supercooled liquid:
The dynamics that is probed needs to reflect the intermolecular dynamic
heterogeneity, and must not be superimposed by effects of intramolecular
dynamic heterogeneity.
