Far-infrared Detection of C₃ in Sagittarius B2 and IRC +10216

Abstract

We report on the detection of nine lines of the ν₂ bending mode of triatomic carbon, C₃, in the direction of Sagittarius B2. The R(4) and R(2) lines of C₃ have been also detected in the carbon-rich star IRC +10216. The abundances of C₃ in the direction of Sgr B2 and IRC +10216 are ~=3×10^-8 and ~=10^-6, respectively. In Sgr B2 we have also detected the 2₃-1₂ line of NH with an abundance of a few times 10^-9. Polyatomic molecules will have a weak contribution from their pure rotational spectrum to the emission/absorption in the far-infrared. We suggest, however, that they could be, through their low-lying vibrational bending modes, the dominant carriers of emission/absorption in the spectrum of bright far-infrared sources. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) and with participation of ISAS and NASA.