ELECTRON-CAPTURE INDUCED PROCESSES IN MOLECULES AND MOLECULAR AGGREGATES

Negative ion formation following resonant electron capture by molecules and molecular aggregates is studied in beam experiments for some prototype systems (CF3Cl, CF4, C2F4, CF3Cl/H2O). Analysis of the excess kinetic energy of the reaction products is performed in order to observe the change in decomposition dynamics on proceeding from single molecules to clusters. It is shown that electron capture by aggregates may ultimately generate monomeric anions in their relaxed geometries which are not accessible in the isolated compound. In some cases a relaxation energy of several electronvolts has to be distributed among the target cluster. Fragment ions formed with remarkably high translational energy are effectively slowed down when arising from aggregates at the same attachment energy. Clusters of tetrafluoroethylene show an additional resonance at low attachment energies; these exclusively decompose into (C2F4)-n, n ≥ 2. Aggregates composed of H2O and CF3Cl give rise to the solvated ions (H2O)n·Cl- (n ≥ 1), (H2O)n·F- (n ≥ 1) and (H2O)n·OH- (n ≥ 2). In the case of (H2O)n·Cl- it is shown that the formation probability depends strongly on the electronic state of the precursor anion within the cluster. © 1990.