Discrete-continuum and discrete-discrete interactions in the autoionization spectrum of (BH)-B-11

We have applied triple-resonant optical photoionization spectroscopy to characterize the lineshapes of autoionizing Rydberg resonances in (BH)-B-11 converging to the X-2 Sigma(+) ground state of (BH+)-B-11 in vibrational levels from v(+)=0 through 4. Third photon transitions originating from the B-1 Sigma(+) v ’=0, 1, 2 or 3 states of (BH)-B-11 reach high Rydberg resonances in Delta v=0 ( below vertical threshold) and Delta v=1 ( above vertical threshold) transitions. Observed spectra display contributions from discrete-continuum and discrete-discrete transition moments, where intensities are governed by Franck-Condon factors and the discrete-continuum mixing of final states. The spectra show Fano line profiles attributable to the phase interference between competing photoionization/photodissociation transition moments. Two fitting parameters, q and Gamma, which characterize asymmetric spectral lineshapes in terms of an interaction between a single discrete state and single continuum, serve well to model the photoionization cross-section. Quantitative trends in these parameters yield insight into the discrete-continuum coupling of final states, driven by differences between the electronic potentials of the gateway 3s sigma B (1)Sigma(+), 3p pi D (1)Pi and 3p sigma E (1)Sigma(+) states of (BH)-B-11 and that of the X (2)Sigma(+) ground state of the cation.