Evidence for the weak steric hindrance scenario in the supercooled-state reorientational dynamics.

We use molecular-dynamics computer simulations to study the translational and reorientational dynamics of a glass-forming liquid of dumbbells. For sufficiently elongated molecules the standard strong steric hindrance scenario for the rotational dynamics is found. However, for small elongations we find a different scenario--the weak steric hindrance scenario--caused by a new type of glass transition in which the orientational dynamics of the molecule's axis undergoes a dynamical transition with a continuous increase of the nonergodicity parameter. These results are in agreement with the theoretical predictions by the mode-coupling theory for the glass transition.