Spectroscopy and potential inversion for the predissociated C 1Π state of AlBr. Electronic structure of group IIIa halides

Abstract

Using frequency-doubled pulsed dye-laser radiation, the spectra of the C 1Π-X 1Σ + system of AlBr have been recorded. Dunham parameters, RKR curves and Franck-Condon factors are calculated from transitions to not significantly predissociated levels of the C 1Π state. The quantitative description of predissociation is based on tunneling through a potential barrier. The full potential curve of the C 1Π state is derived directly by a nonlinear fit procedure from measured energy positions of bound and quasi-bound levels and predissociation rates which were determined directly from linewidths and from fluorescence intensities of the investigated fine structure. The potential curve clearly shows a maximum at medium internuclear distance. In a systematic context of the group IIIa metal halides it is qualitatively shown that strong avoided crossings of bound ionic states arising from different ionic asymptotes and repulsive covalent states arising from the asymptotes of the atomic ground states, e.g. metal 2P, halogen 2P, create potential maxima, which are responsible for predissociation by tunneling.