Unidentified Interstellar Microwave Line

Abstract

DURING a search for H¹²C¹⁴N (hydrogen cyanide) and its molecular isotope H¹³C¹⁴N, we have detected a new molecular line. The discovery was made in June 1970 using the 36-foot telescope of the National Radio Astronomy Observatory in Tucson, Arizona. The receiver was a 3-mm mixer radiometer developed by NRAO in conjunction with Jefferts, Wilson and Penzias of the Bell Telephone Laboratories. The single sideband noise temperature of the radiometer was 3000 K and it covered frequencies from 85 to 90 GHz. At these frequencies the telescope has a beamwidth of 1′ of arc and a beam efficiency of 50 per cent under optimum conditions. The filter bank receiver used consisted of forty filters spaced 1 MHz apart covering a velocity range of 130 km s⁻¹.