15min:

XIUJUAN ZHUANG, TIMOTHY C. STEIMLE, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287; N. REILLY, D. KOKKIN AND M. C. MCCARTHY, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA; J. F. STANTON, Chemistry Department and Biochemistry, U. of Texas, Austin, TX 78712, USA; T. D. CRAWFORD AND B. FORTENBERRY, Chemistry Department, Virgina Tech, Blackbury VA 24061, USA; J. P. MAIER, Department of Chemistry, University of Basel, Basel, Switzerland.

We report the first recording of the visible spectrum of gas-phase Si₃. 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 1³A₁''- ãA₂' transition of the D_3h isomer based upon new and previous predictions. A vibrational progression observed in the dispersed fluorescence having a spacing of 505 cm^-1 is in agreement with previous ZEKE studies. An additional vibrational progression observed in dispersed fluorescence having a spacing of 173 cm^-1 is in agreement with the bending frequency for the X¹A₁ state of the C_2v isomer estimated from the pure rotational spectrum.