Observations of Cumulene Carbenes, H2CCCC and H2CCC, in TMC-1

The carbon chain molecule H2CCCC was detected in the dark cloud TMC-1 for the first time in the course of a molecular line survey using the Nobeyama 45-m telescope. From nine transitions observed in the frequency region of 17-45 GHz, the total column density of H2CCCC in TMC-1 was derived to be 7.5(±2.0) × 1012 cm-2, which is about half of the value reported in IRC+ 10216. Five transitions of a related carbon chain molecule, H2CCC, were also detected in TMC-1. The column density of H2CCC obtained in TMC-1, 2.8(±0.9) × 1012 cm-2, is a factor of three smaller than that of H2CCCC. The ortho-to-para abundance ratios of H2CCCC and H2CCC were found to be 4.2(±1.5) and 5.9(±2.0), respectively. The chemical reactions of these carbon-chain molecules in dark clouds are discussed.