Add time:08/03/2019         Source:sciencedirect.com

As a part of our efforts to characterize the electron attachment reactions of the group IV tetrahalides, XY4 (X = C, Si, Ge and Y = F, Cl, Br) we here follow up on our previous study on XF4 and report electron attachment to the tetrabromides: CBr4, SiBr4 and GeBr4 in the incident electron energy range from about 0 to 10 eV. The formation of Br−, XBr3−, XBr2− and Br2− is observed from all these compounds, and additionally the molecular anion is observed from SiBr4. The main DEA contributions from CBr4 and GeBr4 are observed through a low lying resonance, which we assign as a T2 shape resonance associated with a single occupation of the t2 symmetry LUMO+1 of these molecules. This resonance is also apparent in the ion yield from SiBr4, but there the main contributions are the molecular anion and Br− in a narrow energy range peaking at 0 eV. We attribute these 0 eV contributions to a vibrational Feshbach resonance associated with the a1 symmetry LUMO. Further resonances are observed, for all the compounds investigated here, in the energy range between 3 and 6 eV. To establish the thermochemical thresholds for the individual channels we have conducted DFT calculations from which we report the threshold values, bond dissociation energies and electron affinities for individual fragments and their neutral precursors. These values are compared to values in the literature where available, and discussed in the context of our experimental results.

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