Paper SS2-TuA9
Dissociative Attachment of Adsorbed Methyl Halides by Dielectric Layer Image State Electrons

Tuesday, October 16, 2007, 4:20 pm, Room 611

We have studied the transfer of low-energy electrons through thin films of n-hexane (C₆H₁₂) on a Cu(110) substrate. The band structure of the thin n-hexane layers allows relatively long-lived image states to be formed at the hexane-vacuum interface.^1,2 In our experiments, these image states are occupied by sub-vacuum level photoelectrons from the Cu(110) substrate that are generated by a near-UV laser, and tunnel through the n-hexane film into the image states. These image state electrons can couple to the unoccupied electron affinity levels of coadsorbed CH₃X (X=Br, I). Dissociative electron attachment (DEA) of the CH₃X is detected by the fission of the C-X bond, with the CH₃ fragment escaping into the vacuum and subsequently detected by a quadrupole mass spectrometer. The intermediary role of the image states in this DEA process is determined from the coverage dependencies of the CH₃ fragment yields and the distinctive translational energy distribution of the CH₃- the image state electrons constitute a nearly monochromatic electron source for DEA of the CH₃X.

¹M.W. Cole, Phys. Rev. B 3 (1971) 4418.
²K. Nagesha and L. Sanche, Phys. Rev. Lett. 81 (1998) 5892.