Calculations of 1 eV–3 keV oxygen scattering from Ag(111) using a b i n i t i o pair potentials

Abstract

Classical trajectory calculations, using an ab initio Ag–O potential, are presented of O2 scattering from Ag(111) in a broad energy range. These calculations can explain the results of various O2/Ag(111) scattering experiments performed at different energies. For O2 scattering around 1 eV, the experimentally observed angular broadening in the scattered signal can be explained as an onset of surface rainbows. The degree of dissociation observed in scattering around 200 eV (incoming angle with respect to surface normal (θi=70°) and around 2 keV θi=85°) can be explained by a collision-induced dissociation. Since O2/Ag(111) is a very corrugated system, we also studied the effect of the parallel velocity on the scattering. With constant normal velocity, the ‘‘largest corrugation’’ (most energy loss and dissociation) occurs for θi between 30° and 60°. For grazing incidence (θi≊85°), the scattering shows the characteristics of scattering from a flat surface: energy losses only decrease the normal component of the incident velocity and energy losses and fractions of dissociated molecules are independent of the parallel component. However, the molecule gets more rotationally excited than in the case of scattering from a flat surface with the same normal incident velocity. Finally, we investigated the relative amounts of vibrational and rotational excitation leading to dissociation. For a flat surface, the dissociation turns out to be mostly due to vibrational excitation, but for a corrugated surface, also rotational excitation largely contributes to dissociation.

Scattering aligned NO+ on Ag(111): The effect of internuclear-axis direction on NO− and O− product formation

“…Previous studies have usually claimed that rotational excitation is the dominant contributor to CID. 71,[79][80][81][82][83] Because of the qualitative agreement between our CTC and the experiment, the model presented in Sec. V was used to help resolve this open question.…”

“…This observation is consistent with the simulations of van den Hoek and Kleyn, where nondissociating trajectories have, on average, more internal energy at impact than after the collision. 71 In summary, the optimal dissociation regime occurs around 25°where rovibrational excitation is large and damping from the surface is reduced to a minimum.…”

“…The CTC of Kleyn and co-workers show that dissociative scattering on a corrugated surface at normal incidence is more likely to occur via rotational excitation, whereas normal incident scattering on a flat rigid surface promotes vibrationally mediated dissociation. 71 They also observed that the CTC results on the flat rigid surface were insensitive to the choice of repulsive gas/surface potential. 71 Our model embodies normal incident scattering on a flat, nonrigid surface.…”

“…70 The HF curves were fit in a fashion similar to that of Kleyn and co-workers. 71 The Morse parameters were chosen to match those of isolated neutral NO in its ground electronic state. For comparison with the experimental data, trajectories were run as a function of collision energy and approach geometry in order to ascertain dissociation dependencies.…”

Rotational excitation in scattering of hyperthermal NO from Pt(111)

“…39 In a perfect chattering collision all of the translational energy is transferred to rotation on the initial impact, then back into translation as the other end strikes the surface, leaving the molecule with no rotational excitation. For initial conditions slightly different from the perfect chattering condition, it can be expected that the rotational excitation will vary widely.…”