Desorption of fragment ions from mono-and multilayered CCl4 on Cu(100) by inner-shell photoexcitation

Photon-stimulated desorption of fragment ions from mono- and multilayered CCl4 on Cu(100) has been investigated using synchrotron radiation in the photon-energy range from 2810 to 2850 eV. For monolayer, only Cl+ ions were desorbed. The desorption of the Cl+ ions happens only at the Cl 1s-->sigma* resonant excitation which mainly ends up in the v(-4) sigma* state (v denotes the valence orbital). The result shows that the v(-4) sigma* state survives even in the strong coupling system due to the fast bond-breaking process. In contrast, both the Cl+ and CCl3+ ions were desorbed from multilayer where the coupling between adsorbate and substrate is weak. The desorption yield of the CCl3+ ions is almost proportional to the X-ray absorption yield regardless of the final electronic configuration. The desorption of the molecular fragment-ions is interpreted by the effect of Auger-stimulated secondary electrons due to the relatively slow movement of the heavy molecular species. (C) 1998 Elsevier Science B.V. All rights reserved.