Collision-induced activation of the β-hydride elimination reaction of isobutyl iodide dissociatively chemisorbed on Al(111)

Abstract

The collision-induced activation of the endothermic surface reaction of isobutyl iodide chemisorbed on an Al(111) surface is demonstrated using inert-gas, hyperthermal atomic beams. The collision-induced reaction (CIR) is highly selective towards promoting the β-hydride elimination pathway of the chemisorbed isobutyl fragments. The cross section for the collision-induced reaction was measured over a wide range of energies (14–92 kcal/mol) at normal incidence for Ar, Kr, and Xe atom beams. The CIR cross section exhibits scaling as a function of the normal kinetic energy of the incident atoms. The threshold energy for the β-hydride elimination reaction calculated from the experimental results using a classical energy transfer model is ∼1.1 eV (∼25 kcal/mol). This value is in excellent agreement with that obtained from an analysis of the thermally activated kinetics of the reaction. The measured cross section shows a complex dependence on both the incident energy of the colliding atom and the thermal energy provided by the surface where the two energy modes are interchangeable. The dynamics are explained on the basis of an impulsive, bimolecular collision event where the β-hydride elimination proceeds via a possible tunneling mechanism. The threshold energy calculated in this manner is an upper limit given that it is derived from an analysis which ignores excitations of the internal modes of the chemisorbed alkyl groups.

Collision-Induced Desorption and Reaction on Hydrogen-Covered Al(111) Single Crystals: Hydrogen in Aluminum?

“…The surface area on which an atomic impact yields a desorption event per adsorbed molecule (either H or AlH 3 ) is the desorption cross-section, Q D . Ceyer et al described this relationship thoroughly in the context of a now classic study of the methane/Ni(111) system. ,, Following that work, the cross section for desorption as a function of the collision energy, flux of the beam (oriented normal to the surface), and the surface coverage can be written as where E i is the energy of the incident beam, F B is the total flux in atoms/cm 2 , q ( t ) is the time dependent surface coverage, and t is the time of exposure to the incident beam.…”

“…The experiments for this study were performed in a three-stage UHV chamber that has been described in detail previously. , The first two stages of the chamber are used for beam generation. The beam is formed by a constant adiabatic expansion of the gas from a 25 mm molybdenum aperture.…”

Surface Processes Induced by Collisions

“…3,4 The CID of NH 3 and C 2 H 4 from Pt(111) was reported by Levis and co-workers, 5,6 O 2 from Pt(111) by Kasemo et al, 13 O 2 from Ag(110) by Rocca and co-workers, [10][11][12] Xe from Pt(111) by Rettner et al, 8a Ar from Ar covered Ru(001) by Head-Gordon et al, 8b N 2 from Ru(001) by Romm et al, 9 and water from Ru(001) by Asscher and coworkers. 7 Collision induced dissociation of adsorbed species was reported so far in the case of CH 4 on Ni(111), when energetic Xe atoms striked this surface to produce adsorbed methyl and hydrogen as a competing channel to the CID of methane, Ceyer et al 14,15 In addition, experiments have demonstrated the possibility for intramolecular, Nuzzo et al, 16 and bimolecular (CO oxidation to CO 2 ), Kasemo et al, 17 reactions induced by hyperthermal projectiles. Collisions of rare gas atoms on a hydrogen saturated Ni(111) resulted in a collision induced transition of surface hydrogen into subsurface atoms, as reported by Ceyer and co-workers.…”

Chemistry and Atomic Distortion at the Surface of an Epitaxial BaTiO3 Thin Film after Dissociative Adsorption of Water

“…Chemisorption occurs through bond formation. One way of enhancing this can be direct collisional activation; however, more importantly, chemisorption can be enhanced by precursor-mediated adsorption, where the molecule is first trapped in a weakly bound physisorbed state, which is a precursor for the formation of chemical bonds. , In this case, impinging water molecules get trapped into a shallow physisorption well, dominated by van der Waals interactions and static charge on the surface. These interactions are not sufficiently strong to fix the water molecule at the initial adsorption sites and the trapped precursor can migrate over the surface.…”