Propynylidyne
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IUPAC name
1,2-Propadien-1-yl-3-ylidene
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| Other names
2-Propyn-1-ylidyne; 2-Propynylidyne
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3D model (Jmol)
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| Properties | |
| C3H | |
| Molar mass | 37.04 g·mol−1 |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| Infobox references | |
Propynylidyne is a chemical compound that has been identified in interstellar space.
μD=3.551 Debye
2Π electronic ground state
A rotational spectrum of the 2Π electronic ground state of l-C3H can be made using the PGopher software (a Program for Simulating Rotational Structure, C. M. Western, University of Bristol, http://pgopher.chm.bris.ac.uk) and molecular constants extracted from the literature. These constants include μ=3.551 Debye and others provided by Yamamoto et al. 1990, given in units of MHz: B=11189.052, D=0.0051365, ASO=432834.31, γ=-48.57, p=-7.0842, and q=-13.057. A selection rule of ΔJ=0,1 was applied, with S=0.5. The resulting simulation for the rotational spectrum of C3H at a temperature of T=30K agree well with observations. The simulated spectrum is shown in the figure at right with the approximate atmospheric transmission overplotted in blue. All of the strongest simulated lines with J < 8.5 are observed by Yamamoto et al.
μD=2.4 Debye electronic ground state
The molecule C3H has been observed in cold, dense molecular clouds. The dominant formation and destruction mechanisms are presented below, for a typical cloud with temperature 10K. The relative contributions of each reaction have been calculated using rates and abundances from the UMIST database for astrochemistry.
The C3H molecule provides the dominant pathway to the production of C4H+, and thereby all other CnH (n>3) molecules via the reactions:
These reactions produce the majority of C4H+, which is necessary for the production of higher-order carbon-chain molecules. Compared to the competing reaction,
C3H3+ + C → C4H2+ + H,
also shown right, the destruction of C3H provides a much faster pathway for hydrocarbon growth.
Other molecules in the C3H family, C2H and C3H2, do not significantly contribute to the production of carbon-chain molecules, rather forming endpoints in this process. The production of C2H and C3H2 essentially inhibits larger carbon-chain molecule formation, since neither they nor the products of their destruction are recycled into the hydrocarbon chemistry.
The first confirmation of the existence of the interstellar molecule C3H was announced by W.M Irvine et al. at the January 1985 meeting of the American Astronomical Society. The group detected C3H in both the spectrum of the evolved carbon star IRC+10216 and in the molecular cloud TMC-1. These results were formally published in July of the same year by Thaddeus et al. A 1987 paper by W.M. Irvine provides a comparison of detections for 39 molecules observed in cold (Tk ≅10K), dark clouds, with particular emphasis paid to tri-carbon species, including C3H.
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