15min:

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

The rotational spectrum of rhomboidal SiC₃ in its ¹A₁ electronic ground state was measured in a laboratory discharge of silane and acetylene by Fourier transform microwave spectroscopy and direct absorption millimeter wave spectroscopy. A full structure derived from observations of isotopically substituted species shows that SiC₃ has a planar geometry with C_2v symmetry that consists of atoms in the shape of a distorted four-member ring and a transannular carbon-carbon bond. Following the laboratory detection, seven rotational transitions of SiC₃ near 100 GHz were detected in the circumstellar envelope of the evolved carbon star IRC+10216 using the NRAO 12~meter telescope.