VACUUM-ULTRAVIOLET FLUORESCENCE EXCITATION SPECTROSCOPY OF BBR3 IN THE RANGE 8-20 EV

The vacuum ultraviolet and visible spectroscopy of BBr3 using fluoresc ence excitation and dispersed emission techniques is reported. Spectra have been recorded following excitation using synchrotron radiation i n the energy range 8-20 eV. Rydberg transitions of BBr3 have been obse rved and assigned. Analysis of the Rydberg spectra shows that the rela tive order of the three highest occupied valence molecular orbitals of BBr3 is 3e' < 1e '' < 1a(2)'. The Rydberg states have been shown to f ragment to form fluorescing states of BBr and BBr2. The dispersed emis sion spectrum of the BBr2 radical has been identified. Fluorescence wa s observed between 240 nm and 390 nm and the emission has been attribu ted to at least two distinct BBr2 electronic transitions. Lifetimes of 18 +/- 2 ns and 24 +/- 2 ns have been measured for the emitting state s. Emission from the (D) over tilde(2)E' state to the (X) over tilde(2 )A(2)' state of BBr3+ has also been observed between 350 nm and 440 nm . The threshold for the production of fluorescence from (D) over tilde (2)E' BBr3+ has been determined to be 13 . 93+/-0 . 02 eV. High lying vibrational levels of (D) over tilde(2)E' BBr3+ produced at excitation energies greater than 15 . 8 +/- 0 . 2 eV may also dissociate to form fluorescing states of BBr2+. Emission from these fragments has been o bserved between 250 nm and 300 nm. At higher excitation energies the B Br3 molecule has been shown to dissociate to produce isolated boron an d bromine atoms. Thresholds for fragmentation to form excited S-2 and D-2 states of boron have been determined to be 16 . 3 +/- 0 . 2 eV and 17 . 4 +/- 0 . 2 eV, respectively.