Knowledge Bank

We have generated SiCN in supersonic free jet expansions, and observed the laser induced fluorescence (~LIF~) of the vibrationally hot bands of the $A~$ $2\Delta$ -- $X~$ $2\Pi$ transition. We have measured dispersed fluorescence (~DF~) spectra from the single vibronic levels (~SVL's~), $A~$ $(0110)$ $2\Phi$ and $2\Pi$, and rotationally resolved LIF excitation spectra of the two hot bands, $A~$ $(0110)$ $2\Phi$ -- $X~$ $(0110)$ $2\Delta$ and $A~$ $(0110)$ $2\Pi$ -- $X~$ $(0110)$ $2\Sigma (-)$. The rotational energy levels were reasonably analyzed as those of the $2K\prime$ -- $2K″$ 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 $2\Lambda \prime$ -- $2\Lambda ″$ (~$2\Delta$ -- $2\Pi$~) 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 $|\Lambda v2l\Sigma ;JPMJ⟩$, so-called ''$l$-basis", better describes the system than that of $|\Lambda v2K\Sigma ;JPMJ⟩$.