ELECTRON-CAPTURE AND LOSS IN THE SCATTERING OF FLUORINE AND CHLORINE ATOMS AND IONS ON METAL-SURFACES

We present the results of a study of collisions of 0.5-4 keV fluorine and chlorine negative ions and atoms with Mg, Al and Ag surfaces. Prod uction of negative and positive ions is observed. An electron spectros copy study aimed at identifying excitation of autoionizing states was performed. We report scattered ion fractions as a function of energy a nd exit angle with respect to the surface. For these high electron aff inity systems, the negative ion fractions are very large. Their angula r dependence indicates the existence of a loss process. At low energie s the ion fractions can be described using existing calculations [P. N ordlander, N.D. Lang, Phys. Rev. B, 46 (1992) 2584] of widths of the n egative ion stales in front of a metal surface, once the multielectron nature of the problem, i.e. the fact that the halogen ions have six e ssentially equivalent electrons. is properly taken into account. (C) 1 998 Elsevier Science B.V. All rights reserved.