Detection of vibrationally excited HC7N and HC9N in IRC+10216
Journal article, 2020

Observations of IRC +10216 with the Yebes 40 m telescope between 31 and 50 GHz have revealed more than 150 unidentified lines. Some of them can be grouped into a new series of 26 doublets, harmonically related with integer quantum numbers ranging from J(up)=54 to 80. The separation of the doublets increases systematically with J, that is to say, as expected for a linear species in one of its bending modes. The rotational parameters resulting from the fit to these data are B=290.8844 +/- 0.0004 MHz, D=0.88 +/- 0.04 Hz, and q=0.1463 +/- 0.0001 MHz. The rotational constant is very close to that of the ground state of HC9N. Our ab initio calculations show an excellent agreement between these parameters and those predicted for the lowest energy vibrationally excited state, nu (19)=1, of HC9N. This is the first detection, and complete characterization in space, of vibrationally excited HC9N. An energy of 41.5 cm(-1) is estimated for the nu (19) state. In addition, 17 doublets of HC7N in the nu (15)=1 state, for which laboratory spectroscopy is available, were detected for the first time in IRC +10216. Several doublets of HC5N in its nu (11)=1 state were also observed. The column density ratio between the ground and the lowest excited vibrational states are approximate to 127, 9.5, and 1.5 for HC5N, HC7N, and HC9N, respectively. We find that these lowest-lying vibrational states are most probably populated via infrared pumping to vibrationally excited states lying at approximate to 600 cm(-1). The lowest vibrationally excited states thus need to be taken into account to precisely determine absolute abundances and abundance ratios for long carbon chains. The abundance ratios N(HC5N)/N(HC7N) and N(HC7N)/N(HC9N) are 2.4 and 7.7, respectively.

molecular data

circumstellar matter

stars: carbon

line: identification


stars: individual: IRC+10216


J. R. Pardo

Spanish National Research Council (CSIC)

C. Bermudez

Spanish National Research Council (CSIC)

C. Cabezas

Spanish National Research Council (CSIC)

M. Agundez

Spanish National Research Council (CSIC)

J. D. Gallego

Yebes Observatory

J. P. Fonfria

Spanish National Research Council (CSIC)

Luis Velilla Prieto

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Spanish National Research Council (CSIC)

G. Quintana-Lacaci

Spanish National Research Council (CSIC)

B. Tercero

Spanish National Observatory (OAN)

Yebes Observatory

M. Guelin

Institut de Radioastronomie Millimétrique (IRAM)

J. Cernicharo

Spanish National Research Council (CSIC)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 640 L13

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Theoretical Chemistry



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