A comparative study of the dissociation dynamics of energetic H 2, N 2 and NO scattered from Cu(111) under glancing angles of incidence

We have scattered fast beams of H ₂, N ₂ and NO and their positive ions from Cu(111) under glancing angles of incidence. By directly measuring the relative velocity v of the dissociation fragments of those molecules which dissociatively scatter, we obtain distributions of the kinetic energy released in the H-H, N-N and N-O internuclear coordinate as a function of the final orientation of the internuclear axis. We propose a dissociation mechanism involving repeated electronic excitation-relaxation cycles with the dynamics dominated in the case of H ₂ by the topography of electronically excited states, and in the case of N ₂ and NO by vibrational excitation in the exit channel of the ground state. This interpretation is supported by classical dynamics simulations.