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Beta-diketones are a versatile class of compounds that can complex almost any metal in the periodic table of elements. Their metal complexes are found to be fairly stable and generally have sufficient vapor pressure for deposition techniques requiring volatile metal sources. Motivated by the potential role of low energy electrons in focused electron beam induced deposition, we have carried out a crossed electron/molecular beam study on the dissociative electron attachment and non-dissociative electron attachment (NDEA) to hexafluoroacetylacetone (HFAc) and its bidentate metal complexes: bis-hexafluoroacetylacetonate copper(II), Cu(hfac)2 and bis-hexafluoroacetylacetonate palladium(II), Pd(hfac)2. The relative ion yield curves for the native precursor to the ligand as well as its stable, 16 valence electron Pd(II) complex and open shell, 17 valence electron Cu(II) complex, are presented and compared. For HFAc, the loss of HF leads to the dominant anion observed, and while NDEA is only weakly pronounced for Pd(hfac)2 and loss of hfac- is the main dissociation channel, [Cu(hfac)2]- formation from Cu(hfac)2 dominates. A comparison of the ion yield curves and the associated resonances gives insight into the role of the ligand in the attachment process and highlights the influence of the central metal atom. [ABSTRACT FROM AUTHOR]

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]

Recent results on reactions induced by collisions of low energy electrons (0–15 eV) 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 (SN2) 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). [Copyright &y& Elsevier]