The internal energy distribution of NO and N2 scattering from defective surfaces

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(111) surfaces, with adatoms and with vacancies. Calculations reproduce well the experimental results for NO and N2 scattering from clean surfaces. NO undergoes more extensive rotational excitation than N2 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 11) 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)0(i), switches sign as the incident energy increases. This behavior is also observed in the case of N2 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(111). Adatom defects increase trapping for NO molecules impinging on the surface with glancing trajectories while vacancies have the opposite effect. (C) 2008 Elsevier B.V. All rights reserved.