We have determined the dynamics and energetics of associative desorption of ${\mathrm{N}}_2$ from Ru(0001) using both an experimental technique, laser-assisted associative desorption, and density functional calculations. These show that ${\mathrm{N}}_2$ is preferentially desorbed into very high vibrational states and that the barriers between gas phase ${\mathrm{N}}_2$ and adsorbed N atoms increase from 2 to $>3\mathrm{}$ eV with increasing N coverage on the surface. This experimental technique is found to be quite insensitive to low barrier steps and defects which complicate interpretations from other methods of studying high-barrier surface reactions.

• Received 22 December 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.4906