Vacuum ultraviolet fluorescence excitation spectroscopy of BBr3 in the range 8–20 eV

The vacuum ultraviolet and visible spectroscopy of BBr3 using fluorescence excitation and dispersed emission techniques is reported. Spectra have been recorded following excitation using synchrotron radiation in the energy range 8–20 eV. Rydberg transitions of BBr3 have been observed and assigned. Analysis of the Rydberg spectra shows that the relative order of the three highest occupied valence molecular orbitals of BBr3 is 3e′ < 1e″ < 1a′2. The Rydberg states have been shown to fragment to form fluorescing states of BBr and BBr2. The dispersed emission spectrum of the BBr2 radical has been identified. Fluorescence was observed between 240 nm and 390 nm and the emission has been attributed to at least two distinct BBr2 electronic transitions. Lifetimes of 18±2 ns and 24±2 ns have been measured for the emitting states. Emission from the [Dtilde]2E′ state to the [Xtilde]2A′2 state of BBr+ 3 has also been observed between 350 nm and 440 nm. The threshold for the production of fluorescence from [Dtilde]2E′ BBr+ 3 has been determined to be 13·93±0·02 eV. High lying vibrational levels of [Dtilde]2E′ DDr+ 3 produced at excitation energies greater than 15·8±0·2 eV may also dissociate to form fluorescing states of BBr+ 2. Emission from these fragments has been observed between 250 nm and 300 nm. At higher excitation energies the BBr3molecule has been shown to dissociate to produce isolated boron and bromine atoms. Thresholds for fragmentation to form excited 2S and 2D states of boron have been determined to be 16·3±0·2 eV and 17·4±0·2 eV, respectively.