Tunneling mechanism for the dissociative chemisorption of N₂ on metal surfaces

A quantum mechanical tunneling mechanism is found to describe accurately recent experimental study on the dissociative chemisorption dynamics of nitrogen molecules on metal surfaces. A numerical treatment of the time dependent Schrödinger equation was employed to evaluate the transition probability (S) from N₂-metal to N-metal potential energy surfaces (PES) for two degrees of freedom on a flat and rigid surface. The rapid increase of S with incident kinetic energy, its saturation at energies above the barrier for dissociation and vibrational excitation effects were all in good agreement with the experimental results. The calculated results were found to be very sensitive to the potential topology at the crossing area (seam) between the two PES. This extreme sensitivity may serve as a calibration method for the potential shape, by using experimental data for the relative importance of vibration to translation in promoting the dissociation. Large isotope effects are predicted and confirmed by temperature programmed recombinative desorption experiments of ¹⁴N₂ and ¹⁵N₂ from Re(0001).