15min:

SILVIA SPEZZANO, C. A. GOTTLIEB, M. C. MCCARTHY AND P. THADDEUS, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, and School of Engineering & Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138.

Cyclopropenylidene, c-C₃H₂, is the most widely distributed ring in our galaxy; it has been detected in more than 50 astronomical sources, and its isotopic species c-C₃HD has been observed towards several dense cores in cold dark clouds. Because of the high observed abundance and large deuterium fractionation for this small hydrocarbon ring, other isotopic species of c-C₃H₂ may be good candidates for astronomical detection. For these reasons, an exhaustive isotopic study of c-C₃H₂ has now been undertaken in which rotational spectra of c-C₃D₂, c-C₃HD, and the carbon--13 isotopic species of c-C₃HD and c-C₃H₂ have been detected in the centimeter-wave band by Fourier transform microwave (FTM) spectroscopy between 10 and 40~GHz. For c-C₃D₂, millimeter- and submillimeter-wave spectra were subsequently measured between 140 and 400~GHz. Rotational and centrifugal distortion constants derived either from previous measurements or those predicted from theory are compared with the precise constants determined here.