We present simulations of the motion of a single rigid rod in a disordered
static 2d-array of disk-like obstacles. The rotational, DRβ, and
center-of-mass translational, DCMβ, diffusion constants are calculated
for a wide range of rod length L and density of obstacles Ο. It is found
that DCMβ follows the behavior predicted by kinetic theory for a hard
disk with an effective radius R(L). A dynamic crossover is observed in
DRβ for L comparable to the typical distance between neighboring
obstacles dnnβ. Using arguments from kinetic theory and reptation, we
rationalize the scaling laws, dynamic exponents, and prefactors observed for
DRβ. In analogy with the enhanced translational diffusion observed in
deeply supercooled liquids, the Stokes-Einstein-Debye relation is violated for
L>0.6dnnβ.Comment: 8 pages, 4 figures. Major changes. To be published in Europhysics
Letter