Dynamics of Water Dissociative Chemisorption on Ni(111): Effects of Impact Sites and Incident Angles

The dissociative chemisorption of water on rigid Ni(111) is investigated using a quasiclassical trajectory method on a nine-dimensional global potential energy surface based on a faithful permutation invariant fit of $\sim 25000$ density functional theory points. This full-dimensional model not only confirms the validity of our earlier reduced-dimensional model with 6 degrees of freedom, but also allows the examination of the influence of impact sites and incident angles. It is shown that the reactivity depends on the site of impact in a complex fashion controlled by the topography of the potential energy surface rather than the barrier height alone. In addition, the reaction is promoted by momenta both parallel and perpendicular to the surface, as predicted by the recently proposed sudden vector projection model.

Figure 1

(a) Fixed-site barrier height (in eV) map in the smallest symmetry irreducible triangle within the approximate $C_{6v}$ symmetry. (b)–(d) Fixed-site contour plots of the PES as a function of the vertical distance of ${\mathrm{H}}_2\mathrm{O}$ c.m. ($z_0$) and the distance between the dissociating H atom and c.m. of the molecule ($r$), with other coordinates fully relaxed. The saddle point geometries are inserted in the right upper corner.

Figure 2

The initial lateral coordinates distribution for reactive trajectories in the irreducible triangle at different normal incident energies.

Figure 3

QCT dissociation probabilities of ${\mathrm{D}}_2\mathrm{O}(v_1,v_2,v_3)$ in normal incidence on the 9D and 6D PESs as a function of translational energy (upper panel) and total energy (lower panel). $v_1$, $v_2$, and $v_3$ denote the symmetric stretching, bending, and asymmetric stretching modes of ${\mathrm{D}}_2\mathrm{O}$, respectively. The total energy is relative to the asymptotic potential plus the zero-point energy of ${\mathrm{D}}_2\mathrm{O}$.

Figure 4

Dissociation probabilities of ${\mathrm{D}}_2\mathrm{O}$ with nozzle temperatures at 573 K ($E_t=13.94\mathrm{kcal}/\mathrm{mol}$), 673 K ($E_t=15.68\mathrm{kcal}/\mathrm{mol}$), and 773 K ($E_t=17.71\mathrm{kcal}/\mathrm{mol}$), as a function of the incident angle, with the total translational energy fixed (upper panel) and the normal component of translational energy fixed (lower panel).