LABORATORY DETECTION OF THE CYANOPOLYYNE HC13N

The cyanopolyyne HC13N has been detected in the laboratory, and the fr equency of 21 rotational transitions in the band 5-12 GHz has been mea sured to a few parts in 10(7); correspondingly precise values for the rotational constant and centrifugal distortion constant have been obta ined from a least-squares fit to the data: B-0 = 106.97258(4) MHz, D-0 = 0.092(10) Hz (uncertainties in parentheses are la in the last signi ficant digit). The best lines for astronomical detection of this carbo n chain, longer than any yet detected in space, probably lie in the ba nd 5-30 GHz and can be calculated from B-0 and D-0 to better than 0.1 km s(-1) in equivalent radial velocity.