  We present extensive molecular dynamics simulations of a liquid of symmetric
dumbbells, for constant packing fraction, as a function of temperature and
molecular elongation. For large elongations, translational and rotational
degrees of freedom freeze at the same temperature. For small elongations only
the even rotational degrees of freedom remain coupled to translational motions
and arrest at a finite common temperature. The odd rotational degrees of
freedom remain ergodic at all investigated temperature and the temperature
dependence of the corresponding characteristic time is well described by an
Arrhenius law. Finally, we discuss the evidence in favor of the presence of a
type-A transition temperature for the odd rotational degrees of freedom,
distinct from the type-B transition associated with the arrest of the
translational and even rotational ones, as predicted by the mode-coupling
theory for the glass transition.
