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

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.