@article{0004-637X-513-1-305,
  author={M. C. McCarthy and J.-U. Grabow and M. J. Travers and W. Chen and C. A. Gottlieb and P. Thaddeus},
  title={Laboratory Detection of the Ring-Chain Carbenes HC4N and HC6N},
  journal={The Astrophysical Journal},
  volume={513},
  number={1},
  pages={305},
  url={http://stacks.iop.org/0004-637X/513/i=1/a=305},
  year={1999},
  abstract={The highly polar ring-chain carbenes HC 4 N and HC 6 N, formed by substituting either CN or CCCN for a hydrogen atom in cyclopropenylidene ( c -C 3 H 2 ), were detected in a supersonic molecular beam with a Fourier transform microwave spectrometer. Seven a - and four b -type rotational transitions of HC 4 N and 11 a -type transitions of HC 6 N, each with resolved nitrogen nuclear quadrupole hyperfine structure, were measured between 6 and 21 GHz, yielding precise values for the three rotational constants, the leading centrifugal distortion constants, and the quadrupole coupling constants. Like the hydrocarbon carbenes C 5 H 2 , C 7 H 2 , and C 9 H 2 , both new molecules have a planar ring-chain structures and singlet electronic ground states. The strongest lines of HC 4 N can be detected with a signal-to-noise ratio exceeding 10 in a total integration time of less than 1 s, but the lines of HC 6 N were nearly 100 times weaker.}
}