Vibrational Relaxation of Highly Vibrationally Excited Molecules Scattered from Au(111): Role of the Dissociation Barrier

Abstract

Energy transfer during molecular collisions at a metal surface represents a sensitive probe of the molecule−surface interaction potential. Here, via molecular dynamics calculations on several first-principles neural network potentials, we find that the vibrational energy transfer dynamics of highly vibrationally excited NO and CO molecules scattered from Au(111) are strongly correlated with their respective potential energy landscapes in the vicinity of the dissociation barrier. Our results not only reproduce the observed significantly less vibrational relaxation of CO (v i = 17) than NO (v i = 16) scattered from Au(111) and attribute it to the different dissociation barriers in the two systems, but also show a dramatic change of dynamics due to a minor adjustment of the energy landscape near the barrier in the CO case. We find that the BEEF-vdW density functional based potential largely overestimates the vibrational relaxation of CO (v i = 17) even in the absence of any nonadiabatic energy loss, despite its good description for CO adsorption on Au(111). We also discuss the possibility of integrating the validated adiabatic potential with first-principles determined diabatic states towards a more complete description of the non-adiabatic energy transfer in these benchmark systems.

Vibrational energy transfer in collisions of molecules with metal surfaces

“…113 The Born-Oppenheimer molecular dynamics (BOMD) simulations performed on the new NN-PES revealed a surprisingly large contribution to relaxation from an adiabatic mechanism for NO and CO scattering, arising from the softening of the vibrational potential for high vibrational states. 113,114 Existence of high-dimensional accurate PESs initiated a new wave in MD simulations of diatomic molecules scattering from metal surfaces aiming to overcome the deficiencies of the previous approaches. Recent research carried out by theory groups of Maite Alducin (San Sebastian, Spain), Hua Guo (Albuquerque, New Mexico, USA), Bin Jiang (Hefei, China), Geert-Jan Kroes and Jo ¨rg Meyer (Leiden, The Netherlands), Reinhard Maurer (Warwick, UK), Joseph E. Subotnik (Philadelphia, Pensilvania, USA), and Jean Christophe Tremblay (Metz, France) brought a great deal of improvement in our understanding of the non-adiabatic dynamics at surfaces and was reviewed in detail in ref.…”

“…For modelling of the collisional relaxation of highly vibrationally excited molecules, the energy landscape close to the dissociation barrier is very sensitive to the choice of the functional and strongly affects the predicted outcomes. 113 The Born–Oppenheimer molecular dynamics (BOMD) simulations performed on the new NN-PES revealed a surprisingly large contribution to relaxation from an adiabatic mechanism for NO and CO scattering, arising from the softening of the vibrational potential for high vibrational states. 113,114…”

“…113 The Born–Oppenheimer molecular dynamics (BOMD) simulations performed on the new NN-PES revealed a surprisingly large contribution to relaxation from an adiabatic mechanism for NO and CO scattering, arising from the softening of the vibrational potential for high vibrational states. 113,114…”

“…This prompted several theoretical groups to construct more accurate adiabatic and diabatic PESs paying close attention to the choice of the DFT functional and using neural network methods to reduce the fitting error. Several theory groups produced a set of such potentials with impressive accuracy for NO at Au(111), 69,[110][111][112][113] NO at Ag (111), 114 NO at LiF(001), 111 CO at Au(111), 73,113,115,116 H 2 at Ag(111), 106 and HCl at Au(111) [117][118][119] (see also the perspective paper 120 and review 121 ). For modelling of the collisional relaxation of highly vibrationally excited molecules, the energy landscape close to the dissociation barrier is very sensitive to the choice of the functional and strongly affects the predicted outcomes.…”

Rotationally Inelastic Scattering Dynamics of NO from Ag(111): Influence of Interaction Potentials

“…Molecules can gain or lose vibrational and rotational energy when colliding with a surface on account of the couplings of the internal motion either to the translation or to surface phonons and/or electron–hole pairs . A comprehensive understanding of the energy flow among these different degrees of freedom (DOFs) requires joint efforts of quantum-state-resolved surface scattering experiments , and first-principles molecular dynamics (MD) simulations. , Vibrationally and rotationally inelastic scattering of NO from various noble metal surfaces represent one series of the most experimentally studied systems regarding gas–surface energy-transfer dynamics. − In particular, the strong vibrational relaxation of highly vibrationally excited NO molecules, mainly on Au(111), has attracted much interest as a showcase of the breakdown of the Born–Oppenheimer approximation (BOA) at metal surfaces. − ,− Early experimental evidence suggested the dominant importance of an electron-mediated nonadiabatic mechanism, , but recent calculations based on a global adiabatic potential energy surface (PES) fitted to density functional theory (DFT) points have uncovered an interesting correlation between the dissociation barrier region and the degree of vibrational relaxation via an adiabatic mechanism. − However, the existent strong nonadiabatic interactions largely complicate this system, preventing a quantitative estimate to the accuracy of the adiabatic PES alone. , …”