Six-Dimensional Quantum Dynamics of Adsorption and Desorption ofH2at Pd(100): Steering and Steric Effects

Abstract

We report the first six-dimensional quantum dynamical calculations of dissociative adsorption and associative desorption. Using a potential energy surface obtained by density functional theory calculations, we show that the initial decrease of the sticking probability with increasing kinetic energy in the system H2/Pd (100), which is usually attributed to the existence of a molecular adsorption state, is due to dynamical steering. In addition, we examine the influence of rotational motion and orientation of the hydrogen molecule on adsorption and desorption.

Potential-energy surface forH2dissociation over Pd(100)

“…An increase of the rotational energy implies that states with shorter rotational periods are occupied and those molecules turn out of the favorable orientation again more easely. As a consequence of the reduced steering the inital sticking coefficient reduces 1,22 .…”

“…Here we analyze the physical properties behind the topology of the PES. We note that the results are now sufficiently complete for a six-dimensional quantum-dynamical simulation of the dissociation of H 2 molecules on Pd(100) 22 .…”

“…Summarizing these results it is concluded that the dynamics of the hydrogen molecule on the high-dimensional PES cannot be understood using low-dimensional model surfaces but require a quantum dynamic simulation including all degrees of freedom of the hydrogen molecule. Those calculations have been performed using the calculated PES presented in this paper as an input 22 .…”

“…In particular, the character of the dissociation pathway, whether it is activated or non-activated, is not influenced. This part of the PES determines the dynamics dissociation of the hydrogen molecule 22 . The dependence of the adsorption energy on the layer thickness is more pronounced an the region of the PES corresponding to adsorbed H atoms and strong H-Pd bonds.…”

A note on the vibrational efficacy in molecule-surface reactions

“…31). Thus, since the minimum barrier is a very narrow bottleneck towards dissociation, and since the high barrier requires a high collision energy for the molecule to cross it which in turn makes it difficult for it to be steered [53,54] by the potential forces towards the lowest barrier configuration, only a molecule arriving at the surface with the right orientation and in the right position will cross the barrier. The low degree of steering is displayed in Figs.…”