15min:

CARL A. GOTTLIEB, PATRICK THADDEUS, SANDRA BRÜNKEN, MICHAEL C. MCCARTHY, Harvard-Smithsonian Center for Astrophysics; and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; MARCELINO AGÚNDEZ, JOSE CERNICHARO, Department of Molecular and Infrared Astrophysics, Instituto de Estructura de la Materia, CSIC, 28006 Madrid, Spain; MICHEL GUÉLIN, Insitut de Radioastronomie Millimétrique, 38406 St. Martin d'Hères; and LERMA/Ecole Normale Superieure, 75231 Paris, France.

The negative molecular ion C₃N^- has been detected at millimeter wavelengths in a low pressure laboratory discharge, and then with frequencies in hand in the molecular envelope of IRC+10216. Spectroscopic constants derived from laboratory measurements of 12 transitions between 97 and 378~GHz allow the rotational spectrum to be calculated well into the submillimeter-wave band. Four transitions of C₃N^- were detected in IRC+10216 with the IRAM 30~m telescope at precisely the frequencies calculated from the laboratory measurements. The column density of C₃N^- is 0.5% that of C₃N, or approximately 20~times greater than C₄H^- relative to C₄H. The C₃N^- abundance in IRC+10216 is compared with chemical model calculations, and observations in TMC--1 with the NRAO 100~m Green Bank Telescope (GBT) are discussed. The fairly high concentration of C₃N^- achieved in the laboratory implies that other molecular anions containing the CN group may be within reach.