AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS3+MC-TuM

Paper SS3+MC-TuM11
Line of Sight Techniques: Providing an Inventory of all Species Arriving at and Departing from a Surface

Tuesday, October 3, 2000, 11:40 am, Room 210

Session: Technique Innovations: Experiment, Theory and Simulation
Presenter: R.G. Jones, University of Nottingham, UK
Authors: R.G. Jones, University of Nottingham, UK
A.S.Y. Chan, University of Nottingham, UK
M.P. Skegg, University of Nottingham, UK
Correspondent: Click to Email
Line of sight techniques comprise those methods in which species emanating from a surface (atoms, molecules and radicals) undergo just a single pass through the ionisation volume of a mass spectrometer before being pumped. This is achieved by enclosing the mass spectrometer within a cryoshield fitted with appropriate apertures, such that line of sight is established only between a patch on the sample surface (ca 7 mm diameter) and the ionisation volume. All LOS techniques are inherently angle resolved, free from extraneous signals and have approximately equal detection probabilities for all species. Line of sight temperature programmed desorption (LOSTPD)@footnote1@ is a particularly reliable way of obtaining TPD data. By applying an over pressure of gas to the sample and monitoring the reflected flux, we get line of sight sticking probability (LOSSP) measurements@footnote 2@ giving S to an accuracy of 0.02; while monitoring of the reaction products at constant temperature gives line of sight product desorption (LOSPD) data. These techniques provide new, powerful and reliable ways of studying all aspects of surface kinetics, by allowing an inventory of all species arriving at and departing from a surface, for any combination of partial pressures, surface temperature, surface composition and surface structure. In this paper we illustrate these methods using the reactions of 1-bromo-2-chloroethane (BCE) and ioodotrifluoromethane with Cu(111). For BCE we show that it undergoes non-activated dissociative adsorption with a transition state 13 kJ/mol below zero (0 = molecule at infinity). For CF@sub3@I we observe emission of CF@sub3@ radicals and coupling reactions forming, among others, C@sub2@F@sub4@. @FootnoteText@ @footnote 1@ R.G. Jones and S. Turton, Surface Sci. 377-379 (1997) 719. @footnote 2@ R.G. Jones and C. J. Fisher, Surface Sci. 424 (1999) 127.