Effect of molecular energy content on the dissociative chemisorption of N₂ on Re(0001)

Dissociative chemisorption dynamics of N₂ on Re(0001) was studied by employing molecular-beam methods. The dissociation probability S₀ increases three orders of magnitude from 4×10^-5 to 4×10^-2 upon increasing the normal translational energy of N₂ from 0.05 to 1.5 eV, respectively. These results imply the presence of a barrier for dissociation of 0.6±0.15 eV. The influence of vibrational excitation of the incident molecules on S₀ was investigated. A quantum-mechanical study was carried out to simulate the dissociation dynamics. The calculated results reproduce the experimental S₀ dependence on translational energy over a wide range. The vibrational energy is predicted to be less effective for the enhancement of S₀, in agreement with experiment. The quality of the agreement between the theoretical simulation and the experimental data strongly supports a tunneling process through the adiabatic barrier for dissociation as a key mechanism to explain the dynamics of N₂ chemisorption over Re.