Low energy electron interaction with free and bound SF[sub 5]CF[sub 3]: Negative ion formation from single molecules, clusters and nanofilms.

The interaction of free electrons with the potent greenhouse molecule SF[sub 5]CF[sub 3] 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 SF[sub 5][sup -] formation produced via dissociative electron attachment (DEA) within a resonance located below 2 eV. In clusters, undissociated parent anions SF[sub 5]CF[sub 3][sup -] (and larger complexes containing undissociated anions) are observed in addition to the fragment ions. This indicates that (i) SF[sub 5]CF[sub 3] 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 SF[sub 5]CF[sub 3] exhibits a remarkably strong F[sup -] 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 SF[sub 5]CF[sub 3] on an amorphous H[sub 2]O ice surface is found to be more efficient compared to desorption of SF[sub 5]CF[sub 3] from a Xe surface. The implications of these results for the heterogeneous photochemistry of SF[sub 5]CF[sub 3] adsorbed on ice or dust particles in the Earth’s atmosphere are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]