Electronic emission spectroscopy and decay dynamics of Group IV tetrabromo molecular ions

Abstract

Two broad continuous bands are observed in the visible following electron-impact ionization of an He-seeded molecular beam of SiBr₄. By using tunable vacuum UV radiation from a synchrotron source to measure the threshold energy at which the fluorescence bands occur, it is shown that the bands are related to the initial formation of the C ²T₂ state of the parent ion SiBr⁺₄. By comparison with photoelectron data the bands are assigned to bound–free transitions in SiBr⁺₄ C ²T₂–A²T₂ and X²T₁. Analogous transitions are observed with GeBr⁺₄, but CBr⁺₄ does not fluoresce. The radiative lifetimes of SiBr⁺₄ and GeBr⁺₄ C ²T₂ are 47.6 and 67.1 ns, respectively. The results are compared with the electronic emission spectra of the three tetrafluoro and tetrachloro molecular ions.