Direct Observation of an Intermediate State for a Surface Photochemical Reaction Initiated by Hot Electron Transfer

Abstract

The photoinduced charge transfer that had been suggested to result in the dissociation of phenol on Ag(111) was investigated by two-photon photoemission spectroscopy. An unoccupied intermediate state was positively identified, which was found to be located 3.22 eV above the Fermi level. From the photoelectron energy dispersion, the effective mass of the intermediate state was determined to be (15 +/- 10)m(e) for a 1 ML coverage of phenol. This implies that the excited electron is localized mainly on the adsorbed phenol, forming a molecular resonance state. Polarization dependence of the photoelectron intensity suggested that the initial photoexcitation of the substrate produces hot electrons that scatter into the molecular resonance state, leading ultimately to the dissociation of the adsorbate. These results are the first two-photon photoemission study to characterize the transient anionic state involved in photodissociation of a molecule adsorbed on a metal surface.

Photoinduced Electron Transfer at Molecule−Metal Interfaces

“…Polarization-dependent 2PPE measurements, as described in eqs 20 and 21, have suggested that a σ state in the CO/Cu(111) system was populated by hot-electron transfer . The photochemical cross section was determined to be dependent exponentially on photon energy, which is consistent with hot-electron transfer to an adsorbate resonance energetically located at ∼3.2−3.5 eV above the Fermi level. , Indeed, two-photon photoemission measurements reveal a nondispersive state located at 3.22 eV above the Fermi level on the phenol-covered Ag(111) surface .…”

Electron solvation and solvation-induced crystallization of an ammonia film on Ag(111) studied by 2-photon photoemission

“…We note that the work function drops drastically as we increase Y from 0 to 1 ML, which is due to the interfacial dipole moment resulting from the charge transfer between chemisorbed ammonia and the substrate. 24,25 At 0 ML, the highest energy peak is attributed to the surface state 26 (denoted SS), while the middle peak (marked by an asterisk) should be associated with interband transitions (IBT) [27][28][29] in the bulk, since it is one that does not shift in energy even as we change the surface coverage. At coverages above 0 ML, the SS band disappears while new bands emerge.…”

Stereoselective Photopolymerization of Tetraphenylporphyrin Derivatives on Ag(110) at the Sub‐Monolayer Level

“…[46,47] In particular, the NÀH bond photodissociation threshold was estimated at 4.61 eV, that is approximately 0.4 eV lower than the OÀH analogue in phenol-we therefore expect that aniline residues can form radicals on the silver surface, as reported for phenol. [48,49] Here, the anilino radical formation is employed to covalently bond trans-TPP(NH 2 ) 2 monomers by a radical coupling reaction. Our results indicate that porphyrins form nanowires extending along the substrate [11 0] direction and that the monomers are joined by N=N (azo) links.…”