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 Cl₂⁻ 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 a₁ symmetry LUMOs of those compounds. Contributions from another low-lying resonance, which we assign as a ²T₂ shape resonance associated with the t₂ 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 2 eV, 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 8 eV, 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.