Abstract

Electronic spectra of SiH₃ (silyl radical) have been observed previously¹ by 2 + 1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy in the range of 300–420 nm. Transitions from the silicon 3p_x orbital (the HOMO) to np Rydberg states were observed, these two-photon transitions seem to obey the atomic-like selection rule of Δ/ = 0, ±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 from 460 to 600 nm. The vibrational structure in the three-photon transitions is similar to the two-photon transitions: long progressions in the out-of-plane bending mode. This reflects the change in geometry from pyramidal in the ground state to planar in the excited Rydberg states.

© 1991 Optical Society of America