Laser-Induced Fluorescence Spectroscopy of the BaNC Free Radical in a Supersonic Jet

Abstract

Laser-induced fluorescence spectra of the BaNC free radical in a supersonic jet have been recorded for the first time. A strong and rather complicated excitation spectrum was observed between 18 000 and 19 500 cm - 1 . In the corresponding dispersed fluorescence (DF) spectra, long progressions in the bending mode have been identified. The low frequency of this mode, 70 cm - 1 , for the fundamental demonstrates that BaNC is relatively floppy in the bending coordinate in its ground electronic state. The intensity profiles of the bending progressions suggest that BaNC undergoes a substantial change in its equilibrium bond angle on electronic excitation. This is most likely due to the formation of a bent structure in the excited electronic state. Ab initio calculations conducted in this work suggest that BaNC is linear in its ground electronic state. However, an apparent change in sign of the bending-mode anharmonicity, deduced from the DF spectra, is suggestive of a bent equilibrium structure with a small barrier to linearity.