VACUUM UV FLUORESCENCE EXCITATION SPECTROSCOPY OF BCL3 - ELECTRONIC SPECTROSCOPY OF BCL2, BCL2+ AND BCL3+

The fluorescence processes following vacuum-UV excitation of BCl3 in t he photon range 9-25 eV have been studied using synchrotron radiation. Excitation spectra have been recorded at the UK Daresbury source with no dispersion of the fluorescence. Such spectra give information on t he primary excitation process, i.e. the formation of Rydberg states of BCl3 and electronic states of the parent molecular ion which show rad iative decay. The use of optical filters gives a limited degree of inf ormation on the nature of the emitting species. Using the radiation so urce: in its pulsed, single-bunch mode, lifetimes of the emitting stat es have been measured. Dispersed fluorescence spectra have been record ed at the German BESSY 1 source in Berlin where, by dispersing the vac uum-UV-induced fluorescence through a secondary monochromator, low-res olution information has been obtained on the nature of the emitting sp ecies. For photon energies below 12 eV, photodissociation of Rydberg s tates of BCl3 produces a substantial branching ratio into two, or poss ibly three, excited valence states of the BCl2 radical which fluoresce to its ground state. For energies between 13 and 18 eV, BCl A (1) Pi is produced, leading to emission to its ground state at 272 nm. Emissi on is observed from the (D) over tilde (2)E' excited state of BCl3+ wi th a threshold energy of 15.32 eV, the adiabatic ionisation potential of this state. A weak emission between 280 and 350 nm, having a thresh old for production of 16.75 eV, is assigned to a vibronically resolved electronic transition in the BCl2+ ion, the first observation of a sp ectrum of any kind in this ion. Emission from two excited states of th e boron atom is observed at 209 and 250 nm; the thresholds for these e missions occur at the thermochemical threshold for production of that state of B with three chlorine atoms.