Desorption of molecular and atomic fragment-ions from solid CCl4 and SiCl4 by resonant photoexcitation at chlorine K-edge

Photon-stimulated desorption of atomic and molecular fragment-ions from solid CCl4 and SiCl4 following the CI K-edge excitation has been investigated using synchrotron radiation in the 2810-2850 eV photon energy range. For solid CCl4, the main desorbed species at the Cl 1s-->sigma* resonant photoexcitation were atomic (Cl+) and molecular (CCl3+) fragment ions. The photon-energy dependence of the desorption yield around the Cl K-edge revealed that the CCl3+ yield follows the X-ray absorption spectrum, while the Cl+ ions are desorbed predominantly at the Cl 1s-->sigma* (3p*) resonant photoexcitation. Such dissimilarity of the desorption feature between atomic and molecular fragments was also observed for the Cl+ and SiCl+ desorptions from solid SiCl4 at the Cl K-edge photoexcitation. On the basis of the Auger decay spectra, it was elucidated that the Cl 1s-->sigma*(3p*) excitation is mostly followed by the Cl KL2,3L2,3 spectator decay, which results in the final electronic configuration of v(-4) sigma*(1) where v represents one of the valence levels. While the higher-energy excitations, including shape resonance, are followed by the normal Auger decay, which ends up in v(-4) state. It was concluded that the high desorption yield of the atomic Cl+ ions at the Cl 1s-->sigma*(3p*) resonance can be interpreted by the cleavage of the C-Cl (Si-Cl) bond due to the localization of the spectator electron in the highly antibonding sigma* orbital. (C) 1997 Elsevier Science B.V.