We have studied the associative desorption of N-2 from a Ru(000 1) surface, using a six-dimensional classical trajectory method and a potential energy surface based on density functional theory. The frozen surface and Born-Oppenheimer approximations were used, neglecting phonons and electron-hole pair excitation. Our results show, in agreement with experiments, that only 40% of the potential energy at the barrier is transferred to the translational and rotational degrees of freedom. Our results also show, in disagreement with experiment, high vibrational excitation of the desorbed molecules, suggesting the importance of non-adiabatic effects for this process. (c) 2006 Elsevier B.V. All rights reserved.