@article{1538-4357-498-1-L89,
  author={M. C. McCarthy and M. J. Travers and W. Chen and C. A. Gottlieb and P. Thaddeus},
  title={Laboratory Detection of the Carbon Ring Chain C9H2},
  journal={The Astrophysical Journal Letters},
  volume={498},
  number={1},
  pages={L89},
  url={http://stacks.iop.org/1538-4357/498/i=1/a=L89},
  year={1998},
  abstract={The ring-chain C 9 H 2 molecule, formed by substituting the carbon chain C 6 H for one of the hydrogen atoms of the carbene ring C 3 H 2 , one of the more abundant astronomical molecules, has been detected in the laboratory by Fourier transform microwave spectroscopy. Fifteen a -type rotational transitions between 6 and 14 GHz were measured to 2 kHz or better, and precise values were determined for the rotational and centrifugal distortion constants. With these, the entire radio spectrum can be calculated to better than 1 km s −1 in equivalent radial velocity over the range of interest to radio astronomy. The strongest lines of C 9 H 2 , like those of the smaller ring chain C 7 H 2 , were obtained with a diacetylene-neon discharge but were about 10 times weaker. Ab initio calculations have not been done for C 9 H 2 , and isomeric energies are not known, but by analogy with the shorter members of the sequence, the ring-chain carbene here is probably the most stable structure. Of the many possible isomers of C 9 H 2 , several may lie low enough in energy to be detectable in the laboratory and in space with present techniques. Ions and radicals with ring-chain structures are also excellent candidates for laboratory and astronomical detection.}
}