Astronomical detection of H2CCCC

The carbon-chain carbene H2CCCC, a highly polar isomer of diacetylene recently identified in the laboratory, has been detected in the circumstellar shell of IRC + 10216 with the IRAM 30 m telescope. Eight transitions between 80 and 135 GHz have been assigned, all but two of the ortho symmetry species. The rotational temperature of H2CCCC in IRC + 10216 is 20 + or - 3 K, and the column density averaged over the about 25 arcsec beam of the 30 m telescope at 3 mm is (1.6 + or - 0.4) x 10 to the 13th/sq cm - 6 times that of H2CCC, the first member of this sequence of cumulene carbenes, also recently identified in TMC-1.