Knowledge Bank

Laser fluorescence excitation spectra of the BNe, BAr, and $B-H2$ van der Waals complexes, in the vicinity of the B atomic $2s2p2\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}D\leftarrow 2s22p2p$ transition at 208.9 nm, will be reported. For BNe, partially rotationally resolved bands of the $C2\Delta -X2\Pi 1/2$ and $D2\Pi -X2\Pi 1/2$ transitions, and unstructured excitation in the dissociation continuum to the blue, were observed. For BAr, fluorescence excitation was observed only for the $D2\Pi -X2\Pi 1/2$ transition, while no $B-H2$ fluorescence could be detected in this wavelength range. To detect the non-fluorescing states, fluorescence depletion experiments were carried out. With this technique, the BAr $C2\Delta -X2\Pi 1/2$ transition, and electronic transitions in the $B-H2$ complex, were observed. The BAr($C2\Delta$) and $B-H2\ast$ apparently decay by predissociation and chemical reaction, respectively. The contrasting decay behavior of the excited states of BNe, BAr, and $B-H2$ will be discussed in terms of our knowledge of electronic states of these complexes. Estimated binding energies of the BNe and BAr states will be presented.