DYNAMICS IN NEGATIVE-ION ELECTRON-STIMULATED DESORPTION FROM CONDENSED MOLECULES

The knowledge of desorption dynamics is essential to identify the diff erent reaction steps in negative ion electron stimulated desorption (E SD) from condensed molecules and to determine the importance of energy transfer at each step of this process. For this purpose we have devel oped an experimental set-up to measure the kinetic energy (KE) distrib ution of negative ions emerging from condensed molecules at different angles from the surface normal. We present results concerning O- ESD f rom condensed O, at low energy. The shape and energy positions of the KE distributions obtained clearly indicate that multiple electron scat tering and post-dissociation interactions of O- ions as they receed fr om the solid cannot account alone for the observed spectra and that a strong interaction between the resonnance and the adsorbate must be in voked.