CO Stretch Vibration Lives Long on Au(111)

Abstract

Measured lifetimes of the CO internal stretch mode on various metal surfaces routinely lie in the picosecond regime. These short vibrational lifetimes, which are actually reproduced by current first-principles nonadiabatic calculations, are attributed to the rapid vibrational energy loss that is caused by the facile excitation of electron-hole pairs in metals. However, this explanation was recently questioned by the huge discrepancy that exists for CO on Au(111) between the experimental vibrational lifetime that is larger than 100 ps and the previous theoretical predictions of 4.8 and 1.6 ps. Here, we show that the state-of-the-art nonadiabatic theory does reproduce the long CO lifetime measured in Au(111) provided the molecule-surface interaction is properly described. Importantly, our new results confirm that the current understanding of the adsorbates' vibrational relaxation at metal surfaces is indeed valid.

Vibrational Relaxation Lifetime of a Physisorbed Molecule at a Metal Surface

“…This shows that backbonding is absent in CO/Au, as the CO vibrational frequency (ν 01 ¼ 2131 cm −1 ) is quite close to that of gas-phase CO (2143 cm −1 ), indicating little or no electron transfer to the 2π Ã orbital of CO. Strong backbonding leads to strongly redshifted ν 01 values: for example, 2103 cm −1 [57] and 2070 cm −1 [58] for CO chemisorbed on Pt(111) and Cu(111), respectively. Further evidence that CO is physisorbed to Au comes from density functional theory calculations that predict a binding energy of 0.1 eV [33], similar to the experimentally derived activation energy of desorption. Thus, all available evidence supports the conclusion that CO binds to Au(111) by dispersion forces.…”

“…Physisorbed molecules interacting through dispersion forces with the metal are bound at longer distances and exhibit little or no electron exchange with the metal. Theory predicts physisorbed molecules exhibit longer vibrational relaxation lifetimes [29][30][31][32][33]. This has never been experimentally verified, as physisorbed molecules have very small spectroscopic transition strengths, making vibrational lifetime measurements difficult.…”

“…In essence, the longer range repulsion associated with physisorption limits image charge stabilization of the negative ion state, thus preventing electron transfer. When electron transfer is impossible, we may model the interactions between an oscillating dipole and a jellium electron gas [29][30][31][32] or by density functional perturbation theory following Fermi's golden rule expression for the nonadiabatic vibrational damping [33]. These methods predict vibrational relaxation lifetimes of CO on Au(111) between 250 ps [33] and 0.5-2 ns [29][30][31][32] (see Supplemental Material [45]).…”

Orbital-Dependent Electronic Friction Significantly Affects the Description of Reactive Scattering of N2 from Ru(0001)

“…ODF is thus expected to be important for reactive scattering of molecules from metal surfaces. 18,25−27 However, the pragmatic use of broadening techniques for the calculation of ODF coefficients, which is currently without any alternative for calculating these coefficients on a large scale in the context of dynamical simulations, 25,26,28,29 has recently been criticized to affect the values obtained for these coefficients in a way that is not well-defined within the quasi-static limit of TDPT. 30 Altogether, the LDFA and ODF as formulated and implemented at present both have advantages and disadvantages.…”

Electronic friction coefficients from the atom-in-jellium model for Z=1–92

“…Even though ehp excitations have been neglected in many theoretical studies in the past, which could also explain experimental data [6][7][8][9][10][11][12], recent studies indicate that ehp excitations can play an important role in the dynamics of molecule-surface reactions [13][14][15][16][17][18][19][20][21][22]. For example, vibrational lifetimes of simple diatomic molecules adsorbed on metal surfaces were only explained by going beyond the BO approximation [17,[23][24][25][26][27][28][29][30][31][32][33][34]. Furthermore, experiments with atomic hydrogen beams have confirmed the importance of ehp excitations [35][36][37].…”