The dissociation probability of N-2 on Ru(001) increases from 5 x 10(-7) at a kinetic energy of 0.15 eV to 10(-2) at 4.0 eV. Vibrational excitation of the impinging nitrogen molecules enhances the dissociation more than the equivalent energy in translation. Its relative importance increases as the incident kinetic energy grows. The dissociation was found to be surface temperature independent at all incident kinetic energies, in agreement with theoretical predictions based on quantum mechanical nonadiabatic calculations. These simulations reproduce accurately the kinetic energy dependence of So over the entire energy range, suggesting that N-2 tunnels from the molecular to the adsorbed atomic state through an effective barrier of 2.2 eV.