We report the observation of electronic emission spectra in the tetrahedral molecular ions CF+4 and SiF+4. The spectra are observed at a low rotational temperature (less than 30 K) in a crossed molecular-beam - electron-beam apparatus (Carrington & Tuckett 1980). These spectra are especially interesting because the fluorescing states in the two ions lie up to 10 eV above their lowest dissociation channel (to CF+3/SiF+3 + F; see figure 1), and these states might be expected to decay non-radiatively rather than by a radiative channel. The observation of fluorescence decay from highly excited electronic states of these polyatomic ions is therefore a very surprising phenomenon.
Radiative lifetimes of excited electronic states in molecular ions