Low energy electron interaction with free and bound SF5CF3: Negative ion formation from single molecules, clusters and nanofilms

Abstract

The interaction of free electrons with the potent greenhouse molecule SF5CF3 is studied under different degrees of aggregation: single molecules at collision free conditions, clusters within a supersonic molecular beam and condensed molecules. Electron collisions with single molecules are dominated by SF5− formation produced via dissociative electron attachment (DEA) within a resonance located below 2 eV. In clusters, undissociated parent anions SF5CF3− (and larger complexes containing undissociated anions) are observed in addition to the fragment ions. This indicates that (i) SF5CF3 possesses a positive adiabatic electron affinity and (b) low energy attachment is partly channeled into nondissociative processes when the molecule is coupled to an environment. Electron impact to condensed phase SF5CF3 exhibits a remarkably strong F− desorption signal appearing from a pronounced resonance located at 11 eV while in the gas phase at 11 eV only a weak DEA signal is observed. Electron induced desorption from sub-monolayers of SF5CF3 on an amorphous H2O ice surface is found to be more efficient compared to desorption of SF5CF3 from a Xe surface. The implications of these results for the heterogeneous photochemistry of SF5CF3 adsorbed on ice or dust particles in the Earth’s atmosphere are discussed.