A high-dimensional potential energy surface (PES) for CO interaction with the Au(111) surface is developed using a machine-learning algorithm. Including both molecular and surface coordinates, this PES enables the simulation of the recent experiment on scattering of vibrationally excited CO from Au (111). Trapping in a physisorption well is observed to increase with decreasing incidence energy. While energy dissipation of physisorbed CO is slow, due to weak coupling with both the phonons and electron-hole pairs, its access to the chemisorption well facilitates fast vibrational relaxation of CO through nonadiabatic coupling with surface electron-hole pairs. Energy transfer between molecules and metal surfaces represents a key aspect of surface processes, with important implications in a wide array of interfacial phenomena. There are two major energy exchange channels, namely the adiabatic coupling with surface phonons and the nonadiabatic interaction with electron-hole pairs (EHPs).[1-3] The lifetime of CO(ν=1) adsorbate has been measured to be 1-2 ps on Cu(001), using several experimental techniques.[4-7] Such a short lifetime for a high frequency mode (ω=2129 cm -1 ) can only be explained by its nonadiabatic coupling with surface EHPs, because its direct coupling with the low-frequency phonons is unlikely. This nonadiabatic energy dissipation mechanism has been characterized by various theoretical models, [8][9][10][11][12][13][14][15][16][17][18] cumulating with the latest first-principles calculations that quantitatively reproduced the observed lifetime. [19,20] It was thus a surprise when Shirhatti et al. reported a long lifetime (~10 2 ps) for trapped CO(ν=1) in the scattering of vibrationally excited CO(ν=2) from Au (111).[21] It was postulated that physisorption might be involved, given the relatively low desorption temperature of CO from Au (111).[22] Indeed, a recent density functional theory (DFT) study by Lončarić et al. did find such a physisorption well for CO on Au(111),[23] using the Bayesian Error Estimation Functional method with van der Waals corrections (BEEF-vdW).[24] The lifetime of physisorbed CO(ν=1) was calculated within first-principles many-body perturbation theory and found to be consistent with the experimental value.[21] The long vibrational lifetime was attributed to the weaker couplings with EHPs because of the large distance between the adsorbate and surface. The same argument has also been used to explain the vibrationally hot precursor CH4 on the Ir(111) surface. [25] However, the aforementioned theoretical work was only intended to calculate the vibrational relaxation rate for CO adsorbed on the surface, and it provides information on neither the mechanism and dynamics on how the impinging CO molecules are trapped and then desorbed, nor the accompanying energy dissipation into surface phonons. In principle, Ab Initio Molecular Dynamics (AIMD) can shed light on such issues, but the trapping and diffusion are too rare and too long to be computationally feasible for the onthe-fly ...