Vibrationally Hot Bands of the SiCN (A)over-tilde 2Δ - (X)over-tilde 2Π System

We have generated SiCN in supersonic free jet expansions and observed the laser induced fluorescence (LIF) spectrum. In addition to the vibronic bands from the vibrationless level of the (X) over tilde (2)Pi state, the hot bands from the bending vibrational level, (A) over tilde (01(1)0) (2)Phi - (X) over tilde (01(1)0) (2)Delta and (A) over tilde (01(1)0) (2)Pi - (X) over tilde (01(1)0) (2)Sigma((-)), have been measured. The rotational energy levels were reasonably analyzed as those of the K-2' - K-2 '' transitions, but their line intensities calculated from the Honl-London factors derived in the intermediate case between Hund's case (a) and (b) could not reproduce the observed spectra. The Honl-London factors derived in the (2)Lambda' - (2)Lambda '' ((2)Delta - (2)Pi) transition reasonably reproduced the spectra. It indicates that coupling between the electronic orbital and vibrational angular momenta is weak in the SiCN (2)Delta - (2)Pi system, and a basis set of vertical bar Lambda nu(2) l Sigma(i)J P M-j >, the so-called "l-basis", better describes the system than that of vertical bar Lambda nu(2) K Sigma(i)J P M-j >.