Knowledge Bank

Extensive emission spectra have been obtained by laser excitation of selected bands of the $A~2\Sigma +-X~2\Pi i$ systems of jet-cooled SiCH, SiCD, GeCh and GeCD. Up to four quanta of the Si-C or Ge-C stretching mode and even quanta of the bending mode have been observed by pumping upper state $\Sigma$ vibronic levels. Pumping vibronically induced transitions to upper state $\Pi$ vibronic levels has given further information about odd quanta of the bending mode. The assignments have been fitted using a vibronic coupling matrix that includes spin-orbit coupling. Renner-Teller effects. Fermi resonances, and the interaction between nearly degenerate bending levels of different $\nu 2$ and K. The emission spectra of SiCH and SiCD, with $A\approx ϵ\omega$, are easily assigned and the Fermi resonance interaction between $2\nu 2$ and $\nu 3$ is found to be small. In the germanium species, the spin-orbit coupling is much larger than $ϵ\omega$ and the spectra are more complicated. Levels of different $\nu 2$ with $\Delta \nu 2=\pm 1$ are mixed by a $\Delta P=0,HRT\times HSO$ cross-term of substantial magnitude, disrupting the energy level pattern. Results from the vibronic analyses of all four species will be presented.