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

We report on the detection of nine lines of the nu(2) bending mode of triatomic carbon, C(3), in the direction of Sagittarius B2, The R(4) and R(2) lines of C(3) have been also detected in the carbon-rich star IRC + 10216. The abundances of C(3) in the direction of Sgr B2 and IRC + 10216 are similar or equal to 3 X 10(-8) and similar or equal to 10(-6), respectively. In Sgr B2 we have also detected the 2(3)-1(2) 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.