Six-Dimensional Quantum Dynamics of Dissociation of HCl on Bimetallic Surfaces: Cu/Ag(111) vs. Cu/Au(111)^†

In this study, six-dimensional (6D) time-dependent wave packet calculations were employed to investigate the dissociation of HCl molecules on two bimetallic surfaces, Cu/Ag(111) and Cu/Au(111). These calculations were based on two accurate potential energy surfaces (PESs) constructed using neural network methodology. Density functional theory (DFT) calculations revealed that the static barrier heights for HCl on Cu/Ag(111) and Cu/Au(111) were 0.32 eV and 0.28 eV, respectively. These values are significantly lower than the barrier height on pure Cu(111) (0.52 eV), primarily due to surface strain effects. However, it was found that the 6D dissociation probability of HCl in (v=0, 1, j=0) states on Cu/Au(111) was considerably lower, despite its barrier height being 0.04 eV lower than that for Cu/Ag(111). The underlying mechanism for this observation was attributed to the non-monotonic dependence of the minimum energy path (MEP) on the molecular orientation, which was induced by charge transfer effect for HCl+Cu/Au(111). In contrast, HCl+Cu/Ag(111) exhibited a monotonic dependence. These contrasting behaviors led to distinct differences in rotational alignment and excitation effects for the two reactions.