THE REACTIVITY OF SLOW-ELECTRONS WITH MOLECULES AT DIFFERENT DEGREES OF AGGREGATION - GAS-PHASE, CLUSTERS AND CONDENSED-PHASE

The interaction of Gee electrons in the energy range between 0 and 15 eV with molecules is reviewed. The studies include beam experiments wi th gas phase molecules under collision-free conditions and at higher p ressures, homogeneous and heterogeneous clusters generated in superson ic beams, and molecules adsorbed and condensed on a cold metallic surf ace. In single molecules under collision-free conditions the usual rel axation process of a transient negative ion formed by free electron at tachment is unimolecular decomposition into stable anionic and neutral fragments (dissociative attachment) with cross-sections exceeding 10( -14) cm(2). A remarkable exception is C-60 which forms metastable anio ns C-60(-) up to 14 eV electron energy. In clusters, intramolecular st abilization processes lead to the formation of stabilized molecular an ions. In addition, intramolecular electron transfer processes can stro ngly contribute to anion formation in homogeneous and heterogeneous cl usters. In condensed and adsorbed molecules, finally, effective desorp tion of negative fragment ions is observed when repulsive precursor io ns are involved. The reactivity of transient anions formed by low ener gy attachment is generally strongly quenched with the degree of aggreg ation in favour of associative processes. In the case of core excited resonances, however, the reactivity can be enhanced by the surrounding medium. This effect is explained by the conversion of an open channel resonance in isolated molecules into a Feshbach resonance in clusters and condensed molecules.