Direct and precursor-mediated hyperthermal abstractive chemisorption of Cl2/Al(111)

Abstract

Resonantly enhanced multiphoton ionization (REMPI) and time-of-flight mass spectroscopy have been used to demonstrate that the reaction of Cl2 on the low work function Al(111) surface proceeds via a prompt vertical electron harpooning process. Sticking measurements were performed showing that Cl2 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 Cl2, and indirect, precursor-mediated Cl2. For incident Cl2 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 0.09–0.14 eV. At high surface temperature, 500 K, all incident translational energies and angles yield only the direct channel, with abstracted product energies of 0.19–0.26 eV.