LASER INDUCED FLUORESCENCE SPECTROSCOPY OF JET COOLED SiCN : ROTATIONAL ANALYSIS OF THE HOT BANDS

Abstract

We have generated SiCN in supersonic free jet expansions, and observed the laser induced fluorescence (~LIF~) of the vibrationally hot bands of the $\tilde{A}$ $^2\Delta$ -- $\tilde{X}$ $^2\Pi$ transition. We have measured dispersed fluorescence (~DF~) spectra from the single vibronic levels (~SVL's~), $\tilde{A}$ $(01^10)$ $^2\Phi$ and $^2\Pi$, and rotationally resolved LIF excitation spectra of the two hot bands, $\tilde{A}$ $(01^10)$ $^2\Phi$ -- $\tilde{X}$ $(01^10)$ $^2\Delta$ and $\tilde{A}$ $(01^10)$ $^2\Pi$ -- $\tilde{X}$ $(01^10)$ $^2\Sigma^{(-)}$. The rotational energy levels were reasonably analyzed as those of the $^2K'$ -- $^2K''$ 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 $|\Lambda \; v_2 \; l \; \Sigma; J \; P \; M_J\rangle$, so-called ''$l$-basis", better describes the system than that of $|\Lambda \; v_2 \; K \; \Sigma; J \; P \; M_J\rangle$.