Dissociation dynamics of H2 on Ni(100), Ni(110), and Ni(111) surfaces

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Abstract
A realistic potential energy surface (PES) for the interaction between H2 and Ni surfaces was obtained using a many body expansion approach. Its analytical form is suited for any surface of the Ni crystal so that the parameter values obtained from experimental results or ab initio calculations on one surface can also be used for other faces. We have estimated the parameter values from ab initio cluster calculations on the H2–Ni (100) system. The PES for (100), (110), and (111) surfaces are presented. Using classical trajectories, we have calculated the dissociative sticking probabilities for all three surfaces at a variety of initial translational energies, vibrational states, rotational states, and incident angles. The dissociative sticking probability for the (110) surface is insensitive to the translational energy while that for the (111) surface increases with increasing translational energy. These features are in good agreement with experiments. We also predict that the (100) surface has a dissociative sticking probability which is insensitive to translational energy and is smaller than the (110) surface. The former feature is not in accord with experiment. The reflected molecules are shown to have low rotational energy even for high initial rotational states. Attributes of both the dissociative sticking probabilities and the reflected molecules are correlated with features of the PES. Most notably, we show that very good scaling of the dissociation probability with normal kinetic energy can arise even when the barrier to dissociation is not in the entrance channel (i.e., translational motion perpendicular to the surface) but in the exit channel (i.e., bond stretching of the H2).