Electronic Excitations in the Course of the Reaction of H with Coinage and Noble Metal Surfaces: A Comparison

Abstract

The creation of electronic excitations during the reaction of atomic hydrogen on and with coinage and noble metals has been studied using metal-insulator-metal heterostructures. A characteristic current trace is observed when the outer metal surface of the structure is exposed to a 20 s pulse of H atoms. Comparison to the chemical kinetics allows to disentangle the contributions from the different chemical processes to this current. In the case of the coinage metals studied the observation is interpreted to suggest that predominantly electrons excited in connection with the hydrogen recombination reaction are the source of the current. For Pt such phenomenon is not observed. This difference allows insights into the role of the transition state for the non-adiabaticity in this simple chemical reaction.

Inelastic H and D atom scattering from Au(111) as benchmark for theory

“…First evidence of electronic excitations in H atom interactions with surfaces was provided by experiments using Schottky diodes and metal-insulator-metal devices to measure the chemicurrent produced by H atom adsorption or by the H-H recombination reaction on metal surfaces. [4][5][6][7] The experimental findings inspired several theoretical studies. [8][9][10][11][12] However, the only experimental observable here is the chemicurrent that is strongly dependent on the design of the sensor making comparison to theory difficult.…”

Dynamics of H2 dissociation on the close-packed (111) surface of the noblest metal: H2 + Au(111)

“…Experiments on reaction of H with H adsorbed to Au observe ehp excitation, which has been attributed to the Langmuir-Hinshelwood recombination reaction. 30,31 However, by themselves these experiments give no information on the extent to which ehp excitation affects the reverse dissociative chemisorption probability, and ehp excitation is also observed in experiments on reaction of H with H adsorbed on Cu surfaces 31 although the dissociation of H 2 on Cu( 111) is described quite well with electronically adiabatic theory. 19,20,32 Calculations using ab initio molecular dynamics with electronic friction (AIMDEF) on H 2 + Pd(100) do show that the dissociation of H 2 on a metal surface can be accompanied by substantial energy dissipation to ehps, but this dissipation takes place at the product side of the barrier.…”

Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111)

“…Part of this argument can be based on the findings of recent density functional theory (DFT) calculations, which suggest that the surface reconstruction only has a small influence on the interaction of surface adsorbed H-atoms with Au(111). 59 A further reason for studying H + Au(111) is that, like H + Cu(111), 60 H + Au(111) has been the subject of recent experiments that have measured ehp excitation in interactions of H-atoms with metal surfaces, and have made attempts to determine whether the observed ehp excitation could be attributed to ER or to associative desorption reactions. [60][61][62] Furthermore, experiments using a Schottky diode detector have detected ehp excitation in scattering of thermal H-atoms from Cu and Ag surfaces in the form of chemicurrents, 63 and such experiments have determined ehp excitation energy distributions for both thermal H-and D-atoms scattering from Ag surfaces.…”

“…59 A further reason for studying H + Au(111) is that, like H + Cu(111), 60 H + Au(111) has been the subject of recent experiments that have measured ehp excitation in interactions of H-atoms with metal surfaces, and have made attempts to determine whether the observed ehp excitation could be attributed to ER or to associative desorption reactions. [60][61][62] Furthermore, experiments using a Schottky diode detector have detected ehp excitation in scattering of thermal H-atoms from Cu and Ag surfaces in the form of chemicurrents, 63 and such experiments have determined ehp excitation energy distributions for both thermal H-and D-atoms scattering from Ag surfaces. 64,65 Electron emission from Cu, Ag, and Au surfaces induced by hyperthermal H-and D-atoms incident in plasma beams (with energies between 15 and 200 eV) has been studied by Kovacs et al 66 Much earlier, electron-hole pair excitation induced by hyperthermal Xe and Kr atoms incident on semi-conductor surfaces had been studied experimentally by Weiss et al 67 Scattering of H-atoms from copper surfaces has been investigated with electronically adiabatic models in a number of theoretical studies.…”