title: First astronomical detection of the cumulene carbon chain molecule H2C6 in TMC-1.
abstract: The cumulene carbenes are important components of hydrocarbon chemistry in low-mass star-forming cores. Here we report the first astronomical detection of the long-chain cumulene carbene H2C6 in the interstellar cloud TMC-1, from observations of two of its rotational transitions: J(K,K') = 7(1,7) --> 6(1,6) at 18.8 GHz and 8(1,8) --> 7(1,7) at 21.5 GHz, using NASA's Deep Space Network 70 m antenna at Goldstone, California. In addition we also observed the shorter cumulene carbene H2C4 at the same position. The fractional abundance of H2C6 relative to H2 is about 4.7 x 10(-11) and that of H2C4 is about 4.1 x 10(-9). The abundance of H2C6 is in fairly good agreement with gas-phase chemical models for young molecular cloud cores, but the abundance of H2C4 is significantly larger than predicted.
authors.affiliation: Jet Propulsion Laboratory, Californiia Institute of Technology, Pasadena 91109, USA. langer@langer.jpl.nasa.gov
authors.forename: W D
authors.initials: WD
authors.lastname: Langer
authors.forename: T
authors.initials: T
authors.lastname: Velusamy
authors.forename: T B
authors.initials: TB
authors.lastname: Kuiper
authors.forename: R
authors.initials: R
authors.lastname: Peng
authors.forename: M C
authors.initials: MC
authors.lastname: McCarthy
authors.forename: M J
authors.initials: MJ
authors.lastname: Travers
authors.forename: A
authors.initials: A
authors.lastname: Kovacs
authors.forename: C A
authors.initials: CA
authors.lastname: Gottlieb
authors.forename: P
authors.initials: P
authors.lastname: Thaddeus
mesh_terms: D001256:Astronomy / Q000295:instrumentation*; D002244:Carbon / Q000737:chemistry; D005118:Extraterrestrial Environment; D005740:Gases / Q000032:analysis*; D006838:Hydrocarbons / Q000032:analysis / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D008956:Models, Chemical; D013057:Spectrum Analysis
chemical_list: D005740:Gases; D006838:Hydrocarbons; C030011:carbene; D002244:Carbon; D008697:Methane