Quantum and classical dynamics ofH2scattering from Pd(111) at off-normal incidence

Abstract

We have used the classical trajectory and the time-dependent wave packet methods to study dissociative adsorption, rotational excitation and diffraction of ${\mathrm{H}}_{2}$ colliding with the Pd(111) surface at off-normal incidence. Both methods make use of a potential energy surface obtained from density functional theory calculations. The incidence energies investigated vary from $140\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}230\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. We show that, for fixed incidence energies above $\ensuremath{\simeq}100\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, dissociative adsorption decreases with incidence angle. We also show that molecules that are reflected in an excited rotational state take most of the excitation energy from the normal component of the incident translational energy. First-order diffraction peaks, in particular the out-of-plane ones, are found to be comparable to the specular peak, in agreement with recent experimental results. In most cases, classical and quantum results are in fair agreement, which confirms that classical dynamics methods can be used to analyze the scattering of ${\mathrm{H}}_{2}$ by metal surfaces at off-normal incidence, including diffraction.