@article{0067-0049-189-2-261,
  author={C. A. Gottlieb and M. C. McCarthy and P. Thaddeus},
  title={Vibrationally Excited C6H},
  journal={The Astrophysical Journal Supplement Series},
  volume={189},
  number={2},
  pages={261},
  url={http://stacks.iop.org/0067-0049/189/i=2/a=261},
  year={2010},
  abstract={Rotational spectra of the linear carbon chain radical C 6 H in two low-lying excited vibrational states were observed both at millimeter wavelengths in a low-pressure glow discharge and at centimeter wavelengths in a supersonic molecular beam. Two series of harmonically related lines with rotational constants within 0.3% of the 2 Π ground state were assigned to the 2 Σ and 2 Δ vibronic components of an excited bending vibrational level. Measurements of the intensities of the lines in the glow discharge indicate that the 2 Σ component lies very close to ground, but the 2 Δ component is much higher in energy. The standard Hamiltonian for an isolated 2 Δ state with five spectroscopic constants reproduces the observed rotational spectrum, but several high-order distortion terms in the spin-rotation interaction are needed to reproduce the spectrum of the 2 Σ component in C 6 H and C 6 D. The derived spectroscopic constants allow astronomers to calculate the rotational spectra of the 2 Σ and 2 Δ states up to 260 GHz to within 0.1 km s –1 or better in equivalent radial velocity.}
}