engleski

Dissociative dynamics of O2 on Ag(110)

We have constructed the first full six- dimensional potential energy surface (PES) for O2 on the frozen Ag(110) surface that has a quality of density functional theory (DFT) results. We used the corrugation reducing procedure to interpolate a large number of spin polarized DFT energies resulting in a high quality PES. Our PES reproduces essential features known from other DFT calculations for O2 on Ag(110) such as the lack of entrance energy barriers for molecular adsorption, the existence of four molecular adsorption wells, and the existence of barriers to dissociation. The lowest barrier for dissociation of 0.36 eV from vacuum level is found in a hollow site with the molecule parallel to the surface. This barrier is lower than the ≈ 1.1 eV barriers found in the other flat silver surfaces, in line with the measured much higher reactivity of the (110) surface. Importantly, the constructed continuous PES provides fast evaluation of energy (and forces) for arbitrary molecular configuration, thus making possible to evaluate a large number of trajectories. Having this tool we study the dissociative dynamics of O2 on Ag(110) by performing classical (and quasi- classical) trajectory calculations. Classical dynamics calculations show that at normal incidence conditions no significant dissociation occurs below an initial energy of 0.9 eV (0.6 eV in quasi-classical calculation). This result is an indication of a very reduced configurational space leading to dissociation and also explains why direct dissociation has not experimentally been observed at low incidence energies. Our calculations also show that for non-normal incidence, most of the dissociation takes place close to the long bridge site, that presents a barrier of 0.7 eV, resulting in still lower dissociation probabilities. We have also analyzed the effect of vibrational energy and we have observed that it is very efficient promoting dissociation.

density functional theory

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