===== On Oxygen-terminated Carbon Chain Molecules CnO in Space =====
==== Oxoethenylidene, C2O ====
CCO has been detected first toward TMC-1:\\
M. Ohishi, H. Suzuki, S.-I. Ishikawa, C. Yamada, H. Kanamori, W. M. Irvine, R. D. Brown, P. D. Godfrey, N. Kaifu,\\
**[[https://ui.adsabs.harvard.edu/abs/1991ApJ...380L..39O|Detection of a new carbon-chain molecule, CCO]]**\\
//Astrophys. J.// **380**, L39–L42 (1991).\\
The //NJ// = 12 – 01 and 23 – 12 transitions were detected with the 43 m Green Bank telescope and the 45 m Nobeyama telecope, respectively, at 22258 and 45827 MHz.\\
\\
R. G. Urso, M. E. Palumbo, C. Ceccarelli, N. Balucani, S. Bottinelli, C. Codella, F. Fontani, P. Leto, C. Trigilio, C. Vastel, R. Bachiller, G. A. Baratta, C. S. Buemi, E. Caux, A. Jaber Al-Edhari, B. Lefloch, A. López-Sepulcre, G. Umana, and L. Testi\\
reported on\\
**[[https://doi.org/10.1051/0004-6361/201834322|C2O and C3O in Low-mass Star-forming Regions]]**\\
//Astron. Astrophys.// **628**, Art. No. A72 (2019).\\
The C2O observations were carried out with the IRAM 30 m telescope at 3 mm. Three fine structure components of the //N// = 4 - 3 rotational transition around 92.5 GHz were detected toward the prestellar core L1544. Only the strongest of these components was searched for and detected toward the protostellar Elias 18.
==== Oxopropadienylidene, C3O ====
H. E. Matthews, W. M. Irvine, P. Friberg, R. D. Brown, and P. D. Godfrey\\
reported on\\
**[[https://doi.org/10.1038/310125a0|A new Interstellar Molecule: Tricarbon Monoxide]]**\\
//Nature// **310**, 125–126 (1984).\\
The //J// = 2 − 1 transitions near 19.2 GHz was detected with good signal-to-noise ratio toward TMC-1 using the 43 m GBT.\\
\\
R. D. Brown, P. D. Godfrey, D. M. Cragg, E. H. N. Rice, W. M. Irvine, P. Friberg, H. Suzuki, M. Ohishi, N. Kaifu, and M. Morimoto\\
extended the previous study subsequently in\\
**[[https://doi.org/10.1086/163528|Tricarbon Monoxide in TMC-1]]**\\
//Astrophys. J. // **297**, 302–308 (1985).\\
The //J// = 5 − 4, 8 − 7, and 9 − 8 transitions near 48.1, 77.0, and 86.6 GHz were detected using various telescopes.\\
\\
The molecules was also detected in the circumstellar envelope of the C-rich AGB star CW Leonis by\\
E. D. Tenenbaum, A. J. Apponi, L. M. Ziurys, M. Agúndez, J. Cernicharo, J. R. Pardo, and M. Guélin\\
**[[https://doi.org/10.1086/508166|Detection of C3O in IRC +10216: Oxygen-Carbon Chain Chemistry in the Outer Envelope]]**\\
//Astrophys. J. // **649**, L17–L20 (2006).\\
Observations were carried out at 3 and 2 mm using the ARO 12 m dish and a 3 mm using the IRAM 30 m telescope.\\
M. E. Palumbo, P. Leto, C. Siringo, and C. Trigilio\\
reported on the\\
**[[https://doi.org/10.1086/591017|Detection of C3O in the Low-Mass Protostar Elias 18]]**\\
//Astrophys. J. // **297**, 302–308 (1985).\\
The Noto 32 m dish was employed to serach for the //J// = 4 − 3 transition near 38.5 GHz.\\
==== Oxopentatetraenylidene, C5O ====
J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, R. Fuentetaja, J. R. Pardo, and P. de Vicente\\
reported on the\\
**[[https://doi.org/10.1051/0004-6361/202142634|Discovery of HCCCO and C5O in TMC-1 with the QUIJOTE Line
Survey]]**\\
//Astron. Astrophys.// **656**, Art. No. L21 (2021).\\
Oxopentatetraenylidene, C5O, was identified through six rotational transitions with 11 ≤ //J// ≤ 17 in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope between 31.0 and 50.3 GHz. Four transitions were unblended or only slightly blended, two were somewhat more blended. A value of //T//rot = 10.0 ± 0.5 K was derived through a rotation diagram. C5O is about 50 times less abundant than C2O and about 80 times less abundant than C3O. Only upper limits were derived for C4O and C6O; these were in both cases higher than those of C5O and thus not particularly constraining.\\
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Contributor(s): H. S. P. Müller; 12, 2003; 09, 2012; 12, 2021
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