Surface strain hampers dissociation and induces curious rotational-alignment effect for HCl on the Au/Cu(111) alloy surface.

This article focuses on a six-dimensional quantum dynamics study of hydrogen chloride (HCl) dissociation on a strained pseudomorphic gold (Au) monolayer deposited on a copper (Cu)(111) substrate, using a machine learning-fitted potential energy surface (PES) based on density functional theory (DFT) calculations. The 12.62% compression of the Au monolayer induces a high and late reaction barrier (1.81 eV) with a tight saddle point, significantly suppressing the reactivity of ground-state HCl (v = 0) while substantially enhancing the dissociation probability of vibrationally excited HCl (v = 1), resulting in higher vibrational efficacy compared to HCl on pure Au(111) and Au/Ag(111) alloy surfaces. Additionally, the surface strain causes distinct rotational alignment effects: ground-state HCl dissociation favors a cartwheel alignment (rotation perpendicular to the surface), with high rotational excitation promoting reactivity, whereas vibrationally excited HCl favors a helicopter alignment (rotation parallel to the surface), where rotational excitation is less effective. These findings provide detailed insights into how surface strain influences molecular reactivity and rotational dynamics on bimetallic alloy catalysts, with implications for experimental control of gas–surface interactions and catalyst design.