Six-dimensional quantum dynamics study for the dissociative chemisorption of H₂ on pure and alloyed AgAu surfaces

The 6D time-dependent wave packet calculations were performed to explore H-2 dissociation on Ag, Au, and two AgAu alloy surfaces, using four newly fitted potential energy surfaces based on the neural network fitting to density functional theory energy points. The ligand effect resulting from the Ag-Au interaction causes a reduction in the barrier height for H-2+Ag/Au(111) compared to H-2+Ag(111). However, the scenario is reversed for H-2+Au/Ag(111) and H-2+Au(111). The 6D dissociation probabilities of H-2 on Ag/Au(111) surfaces are significantly higher than those on the pure Ag(111) surface, but the corresponding results for H-2 on Au/Ag(111) surfaces are substantially lower than those on the pure Au(111) surface. The reactivity of H-2 on Au(111) is larger than that on Ag(111), despite Ag(111) having a slightly lower static barrier height. This can be attributed to the exceptionally small dissociation probabilities at the hcp and fcc regions, which are at least 100 times smaller compared to those at the bridge or top site for H-2+Ag(111). Due to the late barrier being more pronounced, the vibrational excitation of H-2 on Ag(111) is more effective in promoting the reaction than on Au(111). Moreover, a high degree of alignment dependence is detected for the four reactions, where the H-2 dissociation has the highest probability at the helicopter alignment, as opposed to the cartwheel alignment.