Negative ion formation through dissociative electron attachment to the group IV tetrachlorides: Carbon tetrachloride, silicon tetrachloride and germanium tetrachloride

The current contribution constitutes the third and final part of our trilogy of papers on electron attachment reactions of the group IV tetrahalides; XY4 (X = C, Si, Ge and Y = F, Cl, Br). In this context we extend our previous studies on XF4 and XBr4 and report results for electron attachment to the tetrachlorides: CCl4, SiCl4 and GeCl4 in the incident electron energy range from about 0 to 10 eV. At the same time we give a summary of the currently available literature on electron interactions with those latter compounds. Upon electron attachment the formation of Cl-, XCl3-, XCl2- and Cl-2(-) is observed from all the tetrachlorides, and additionally the molecular anion SiCl4- is observed from SiCl4. The main DEA contributions are observed through narrow, threshold peaks (at 0 eV) and we attribute these features to single particle resonances associated with the a(1) symmetry LUMOs of those compounds. Contributions from another low-lying resonance, which we assign as a T-2(2) shape resonance associated with the t(2) symmetry LUMO+1, is also observed in the ion yield curves for all the tetrachlorides. The energy of the peak position of those contributions varies in the range from about 1 to 2eV, depending on the compound and the fragment formed. In addition to these low energy contributions, higher energy, fairly broad, features are observed for all the tetrachlorides. These contributions exhibit a peak in the energy range between 5 and 8eV, again depending on the compound and the fragment formed. Further to the experimental data, we report DFT and coupled cluster calculations on the thermochemical thresholds for the individual fragments as well as the respective bond dissociation energies and electron affinities. These calculated values are compared with the experimental appearance energies and literature values, where they are available. (C) 2018 Elsevier B.V. All rights reserved.