Knowledge Bank

Electronic spectra of $SiH3$ (sllyl radical) have been observed previously1 by $2+1$ Resonance Enhanced Multiphoton Ionization (REMPI) Spectroscopy. Predominantly transitions from the silicon $3p1$ orbital (the HOMO) to np Rydberg states were observed. These two-photon transitions seem to obey the atomic-like selection rule of $\Delta 1=0,\pm 2$. which allows transitions to np and nf Rydberg states. New spectra covering the same energy region but using three-photon absorptions have been observed. In these three-photon spectra the transitions to np Rydberg states are practically absent and transitions to ns Rydberg states are strong