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|Section2= |Section3= }} Cyclopropenylidene, or c-C3H2, is an aromatic molecule belonging to a highly reactive class of organic molecules known as carbenes. Due to its reactivity, cyclopropenylidene is only seen terrestrially in the laboratory. However, it is found in significant concentrations in the interstellar medium (ISM) due to the extreme environment. The linear isomer of c-C3H2 is also found in the ISM, but its column density is generally about an order of magnitude lower.〔D. Fosse, J. Cernicharo, M. Gerin, P. Cox "Molecular Carbon Chains and Rings in TMC-1" ''Astrophys. J.'', 552, 168 (2001)〕 ==History== The astronomical detection of c-C3H2 was first confirmed in 1985.〔P. Thaddeus, J. M. Vrtilek, and C. A. Gottlieb "Laboratory and Astronomical Identification of Cyclopropenylidene, C3H2." ''Astrophys. J.'' 299 L63 (1985)〕 Four years earlier, several ambiguous lines had been observed in the radio region of spectra taken of the ISM,〔P. Thaddeus, M. Guelin, R. A. Linke "Three New "Nonterrestrial" Molecules" ''Astrophys. J.'' 246 L41 (1981)〕 but the observed lines were not identified at the time. These lines were later matched with a spectrum of c-C3H2 using an acetylene-helium discharge. Surprisingly, c-C3H2 has been found to be ubiquitous in the ISM.〔Lucas, R. and Liszt, H. "Comparative chemistry of diffuse clouds I. C2H and C3H2" ''Astron. & Astrophys.'', 358, 1069 (2000)〕 Detections of c-C3H2 in the diffuse medium were particularly surprising because of the low densities.〔H. E. Matthews and W. M. Irvine "The Hydrocarbon Ring C3H2 is Ubiquitous in the Galaxy" ''Astrophys. J.'', 298, L61 (1985)〕〔P. Cox, R. Gusten, and C. Henkel "Observations of C3H2 in the Diffuse Interstellar Medium" ''Astron. & Astrophys.'', 206, 108 (1988)〕 It had been believed that the chemistry of the diffuse medium did not allow for the formation of larger molecules, but this discovery, as well as the discovery of other large molecules, continue to illuminate the complexity of the diffuse medium. More recently, observations of c-C3H2 in dense clouds have also found concentrations that are significantly higher than expected. This has led to the hypothesis that the photodissociation of polycyclic aromatic hydrocarbons (PAHs) enhances the formation of c-C3H2.〔J. Pety et al. "Are PAHs precursors of small hydrocarbons in photo-dissociation regions? The Horsehead case" ''Astron. & Astrophys.'', 435, 885 (2005)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cyclopropenylidene」の詳細全文を読む スポンサード リンク
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