15min:

A. J. APPONI, M. C. MCCARTHY, C. A. GOTTLIEB AND P. THADDEUS, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138..

Three new silicon-bearing radicals of astrophysical interest, SiCCH, SiCN and SiNC, were detected in a laboratory discharge in their X² ground states by Fourier transform microwave and direct absorption millimeter-wave spectroscopy. Well-resolved --doubling was observed in both fine structure components, and hyperfine structure was observed in the low rotational transitions of the ² _1/2 ladder. With the spectroscopic constants derived from the laboratory measurements, the spectra of the three radicals can be calculated to an uncertainty of less than 0.1~km~s^-1 in equivalent radial velocity over the entire range of interest to radio astronomers. SiCN with a dipole moment of 2.9~D is probably the most promising of the three for astronomical discovery.