Negative ion resonances of O₂adsorbed on Ag surfaces

Abstract

This article gathers together a collection of recent experimental studies of the adsorption of oxygen on (001), (110) and (111) crystal surfaces of silver with special emphasis on the negative ion states of this model system for oxygen adsorption. These investigations were performed in a network entitled 'Negative ion resonances of adsorbed molecules' supported financially by the European Union within the 'Human capital and mobility programme'. The kinetics and thermodynamics of adsorption are investigated by measuring the sticking coefficient and by thermal desorption spectroscopy (TDS). The vibrational spectra provided by high-resolution electron energy loss spectroscopy (HREELS) are used to analyse the adsorbed species (physisorbed and chemisorbed) in the case of O 2 on Ag(110) and on Ag(111). The mechanisms of inelastic electron scattering by adsorbed O 2 are further investigated with special reference to the negative ion resonances (NIRs), formed by electron capture, which are involved in the electron-molecule collision process.

Femtosecond-laser-driven molecular dynamics on surfaces: Photodesorption of molecular oxygen from Ag(110)

“…III C. However, we have checked that if the surface is allowed to relax, the H001 and H110 adsorption energies increase (in absolute value) to a similar value of around −0.36 eV. Note that the DFT-PBE description of the H001 and H110 adsorption wells seems to be in good agreement with experimental observations [22,23,56,57].…”

“…Adsorption wells at the bridge sites (LB and SB) are further away from the surface compared to the hollow wells. Considering the Z values of the bridge wells, one could be tempted to assign them to the measured physisorption wells [21,22,58]. However, Table I shows that DFT-PBE predicts too large adsorption energies in these wells to be considered as physisorbed states [24].…”

“…As an example, we will employ this methodology to study the laser-induced desorption of O 2 on Ag(110). Due to the importance of oxygen adsorption on silver surfaces in the process of ethylene epoxidation, this system has been a subject of numerous studies [19][20][21][22][23][24]. Using the corrugation reducing procedure (CRP) [11], we have recently constructed the first DFT-based 6D PES for O 2 on Ag(110) and used it to study the dissociative adsorption process [25].…”

Chemistry at molecular junctions: Rotation and dissociation of O2 on the Ag(110) surface induced by a scanning tunneling microscope

“…It also offers an interesting case for fundamental studies of gas-surface interactions because it exhibits physisorption, chemisorption, and molecular dissociation in the same system. A broad range of experiments on O 2 /Ag(110) over the years, 26 including, electron energy loss spectroscopy (EELS), [27][28][29][30] temperature programmed desorption (TPD), 28,30,31 ultraviolet photoemisson, 32,33 electron stimulated desorption ion angular distributions (ESDIAD), 34 near-edge x-ray absorption fine structure studies (NEXAFS), 35, 36 molecular beam studies, 29,37 and STM 24,25,38,39 have determined that (a) O 2 undergoes physisorption at surface temperature, T s < 40 K, chemisorption at 40 K < T s < 175 K, and dissociation at T s > 175 K, (b) O 2 adsorbs parallel to the surface on the fourfold hollow (FFH) site along either the (001) or (110) direction, and (c) the vibrational frequency of chemisorbed O 2 is significantly reduced from its gas-phase value of 1580 cm −1 to 640 cm −1 indicating strong surface-to-molecule electron transfer. Density functional theory (DFT) calculations by Gravil et al [40][41][42] studied the underlying electronic structure of the O 2 -surface bond and confirmed the chemisorption geometry observed by experiment.…”

Image states at the interface with a dipolar organic semiconductor

“…22 Such states therefore no longer possess pure image-state character and a hybrid image/molecular affinity level is created instead. 32 Jensen 33 applied the Rous model to rationalize photodissociation product state distributions of CH 3 Br and CH 3 I on an n-alkane-covered Cu ͑110͒ surface; a key step was identified to be the dissociative electron attachment mediated by an image state. 23,27,28 Theoretical work by Rous based on the Newns-Anderson model suggests considerable enhancement for excitation of image-like states in the event of near-resonance between molecular affinity levels and the image state.…”