The internal energy distribution of NO and N 2 scattering from defective surfaces

Abstract

The internal energy distribution of NO and N 2 scattering from a defective surfaces has been studied using classical molecular dynamics. Stochastic trajectory simulations were used to calculate the final rotational excitation, angular distribution and trapping probabilities of N 2 and NO scattering from clean Ag(1 1 1) surfaces, with adatoms and with vacancies. Calculations reproduce well the experimental results for NO and N 2 scattering from clean surfaces. NO undergoes more extensive rotational excitation than N 2 on clean and defective surfaces. Scattering is more inelastic on defective surfaces and adatoms defects appear to promote rotational excitation more efficiently than vacancies. Trapping exhibits a complex behavior. Dynamical corrugation causes trapping of NO on clean Ag(1 1 1) to exhibit a “crossover” behavior. That is, the value of n in the standard functional dependence of trapping on the incident energy, E i cos n θ i , switches sign as the incident energy increases. This behavior is also observed in the case of N 2 scattering from a surface with adatoms, but in this case is caused by the static corrugation. It appears that the breaking of the 2-D symmetry of the surface (i.e. static corrugation) compensates for the lack of anisotropy in the interaction potential (i.e. dynamical corrugation) for N 2/Ag(1 1 1). Adatom defects increase trapping for NO molecules impinging on the surface with glancing trajectories while vacancies have the opposite effect.