Molecular diffusion across a surface is typically assumed to involve only relatively minor changes in molecular orientation and internal structure. Nevertheless, it is expected (in principle) that certain molecules may diffuse in more complex ways; rolling, deforming, or otherwise adapting their configuration as they make their way across the surface. Here we show that adsorbed benzyne on the Ir {1 0 0} surface displays three distinct diffusional pathways through its configuration space, corresponding to three different values of the molecular tilt. The lowest barrier to diffusion is 1.0 eV. (C) 2002 Published by Elsevier Science B.V.