Low energy electron driven reactions in free and bound molecules: from unimolecular processes in the gas phase to complex reactions in a condensed environment

Recent results on reactions induced by collisions of low energy electrons (0-15eV) with molecules at different degrees of aggregation are reviewed. The studies include crossed electron-molecular beam experiments with gas phase molecules under single collision conditions (effusive beams), homogeneous and heterogeneous clusters (supersonic beams), and experiments in the UHV where molecules are adsorbed and condensed in defined quantities on a cryogenic substrate. In single molecules examples of completely selective bond cleavages via dissociative electron attachment (DEA) are presented. Time-of-flight (TOF) measurements of product ions give access to a detailed study of the energy distribution among the fragments. Probing gas phase biomolecules by low energy electrons and its relevance for radiation damage and cancer therapy is discussed. In clusters we present an example of an ion molecule (S(N)2) reaction in heterogeneous clusters induced by DEA. In the condensed phase low energy electrons can induce desorption of fragment anions via DEA to molecules at the surface. Examples are given for medium enhanced DEA reactions, controlled modifications of surfaces by low energy electrons and (substrate mediated reactions). (C) 2004 Published by Elsevier B.V.