Electronic spectrum of jet cooled SiCN.

We have generated SiCN in a supersonic free expansion, and measured the laser induced fluorescence (LIF) spectrum. Prior to the experiments, ab initio calculations were carried out to obtain the information necessary for searching for the LIF signals. In addition to the X̃ 2Π state, the optimized structures of three excited states, 2Δ, 2Σ+, and 2Σ-, have been obtained. Guided by the predictions, the LIF excitation spectrum of SiCN was observed in the UV region. The rotational structure of the 000 band with the origin, 29 261.639 cm-1, indicated that the electronic transition is à 2Δ-X̃ 2Π. The spin-orbit (SO) constants of the X̃ 2Π and à 2Δ states were determined to be 140.824 and 4.944 cm-1, respectively. In the à 2Δ state, the Fermi resonance between the (0, 20, 0) 2Δ and (0, 00, 1) 2Δ vibronic levels was identified. The molecular constants of the X̃ 2Π state were determined through the simultaneous analysis of the combination differences derived from the present LIF data with the previously reported rotational transitions. The spectroscopic parameters of the à 2Δ state were also obtained from the analysis where the constants of the X̃ 2Π state, derived above, were fixed at those values.