THE VISIBLE SPECTRUM OF Si$_3$

Abstract

We report the first recording of the visible spectrum of gas-phase Si$_3$. A cold molecular beam sample was produced by skimming the output of a pulsed discharge source. The 545-490 nm spectral region was examined using both mass-selected REMPI and pulsed dye laser excitation with LIF detection. Dispersed fluorescence and lifetime measurements of numerous bands were recorded. The spectrum has an origin at 18600 cm$^{-1}$ and a progression in the symmetric stretch with a harmonic frequency of 445 cm$^{-1}$. The bands are assigned to the 1$^{3}$$A$$_1$^{\prime\prime}$- $\~{a}$$A$_2$^{\prime }$ transition of the $D_{3h}$ isomer based upon new and previous \textbf{126}, 074305 (2007)} predictions. A vibrational progression observed in the dispersed fluorescence having a spacing of 505 cm$^{-1}$ is in agreement with previous ZEKE studies \textbf{100}, 1797 (1994)}. An additional vibrational progression observed in dispersed fluorescence having a spacing of 173 cm$^{-1}$ is in agreement with the bending frequency for the $\~{X}^{1}$A$_1$ state of the $C_{2v}$ isomer estimated from the pure rotational spectrum. \textbf{90}, 213003 (2003)}