AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM1
Angular Distribution of Cl Atom Products from Direct and Precursor-Mediated Hyperthermal Abstractive Chemisorption of Cl2/Al(111)

Monday, November 3, 2003, 8:20 am, Room 326

Session: Gas-Surface Dynamics
Presenter: G.C. Poon, University of California, San Diego
Authors: G.C. Poon, University of California, San Diego
A.C. Kummel, University of California, San Diego
Correspondent: Click to Email
Resonantly Enhanced Multiphoton Ionization (REMPI) and Time-of-Flight Mass Spectroscopy (TOF-MS) have been used to demonstrate that the reaction of Cl@sub 2@ on the low work function Al(111) surface proceeds via a prompt vertical electron harpooning process. Sticking measurements were performed showing that Cl@sub 2@ adsorbs via a direct chemisorption process at either high incident translation energy or high surface temperature. However, at glancing incident angles and low surface temperatures (100 K), a precursor-mediated channel predominates. REMPI studies show that fast abstracted Cl was produced via both channels: direct, remotely-dissociated incident Cl@sub 2@, and indirect, physisorption-mediated Cl@sub 2@. An abstraction reaction results in one Cl atom bound to the surface and one Cl atom ejected back into the gas phase. For incident Cl@sub 2@ of 0.11 and 0.27 eV at 40° incident angle and 100 K surface temperature, only the precursor-mediated channel was observed with atomic Cl abstracted product energies of 0.09 to 0.14 eV. At high surface temperature, 500 K, all incident translational energies and angles yield only the direct channel, with abstracted product energies of 0.19 to 0.26 eV. Currently, angular distributions of the ejected Cl atom products are being determined for both direct and precursor-mediated channels. End-on impinging Cl@sub 2@ on the Al surface is expected to promote harpooning and subsequent abstraction products should be directed along the surface normal. Side-on physisorbed Cl@sub 2@ precursor would yield more broadly distributed abstraction products.