The dependence of molecular motion on the dissociative adsorption of H ₂ on Pt(111)

The dependence of molecular motion on the dissociative adsorption mechanism of hydrogen molecule (H₂) on platinum (Pt) surface was studied by Molecular Dynamics (MD) method. An interaction between atoms was considered by the Embedded Atom Method (EAM). A potential between an H atom and a Pt atom was determined from results of Density Functional Theory (DFT). Dissociation probabilities of three surface conditions, that is, (1) when the surface temperature is 300 K, (2) when the surface temperature is 0 K with allowing motion of the surface atoms and (3) when the surface temperature is 0 K with prohibiting motion of the surface atoms, were obtained. From results of the simulations, the effect of surface motion on dissociation probability was analyzed as a function of initial energy of the dissociating molecule or the surface conditions. First, it was concluded that the increase in the dissociation probability of the case (3) by the increase in the initial translational energy of H₂ molecule is gentle compared with those of the other cases. Additionally, the minimum initial translational energy of H₂ molecule of case (3) at which the H₂ molecule can dissociate is the smallest among all of three cases. It was found that this is because the range of the dissociation barrier distribution for the case (3) is wider than those for the other cases due to the thermal motion of surface atoms. Moreover, the effect of translational and rotational motion of molecule on the dissociation probability was analyzed. It was concluded that the dissociation probability increases with the increase in the translational energy while it decreases with the increase in the rotational energy when the rotational energy is small.