Ion desorption induced by core-electron transitions studied with electron-ion coincidence spectroscopy

The recent investigations of ion desorption induced by core-electron transitions using electron-ion coincidence (EICO) spectroscopy are described. In a study of CF(3)CH(OH)CH(3) chemisorbed on a Si(100) surface using photoelectron photoion coincidence (PEPICO) spectroscopy, excitation site-specific ion desorption is directly verified, that is, F(+) desorption is predominant for C 1s photoionization at the -CF(3) site, while H(+) desorption is predominantly induced by C 1s photoionization at the -CH(3) site. A study of condensed H(2)O using Auger electron photoion coincidence (AEPICO) spectroscopy showed that H(+) desorption is stimulated by O KW Auger processes leaving two-hole slates. The H(+) desorption probability is found to depend on the bonding character of the orbitals where holes are created and on the effective hole-hole Coulomb repulsion. AEPICO investigations of H(+) desorption induced by resonant core-electron excitations of condensed H(2)O clearly showed that one-electron-one-core hole or one-electron-two-valence hole states are responsible for the H(+) desorption mechanism. These investigations demonstrate that EICO spectroscopy combined with synchrotron radiation is a novel and powerful tool for the study of ion desorption induced by core-electron excitations. Furthermore, a comparison of PEPICO and photoelectron spectra showed that the surface core-level shift of condensed H(2)O is 0.7 eV. This study shows that PEPICO spectroscopy is also promising as a method to investigate the electronic structure of the specific sites responsible for ion desorption. (C) 2000 Elsevier Science B.V. All rights reserved.