@article{0004-637X-691-2-1494,
  author={H. Gupta and C. A. Gottlieb and M. C. McCarthy and P. Thaddeus},
  title={A Survey of C4H, C6H, and C6H– With the Green Bank Telescope},
  journal={The Astrophysical Journal},
  volume={691},
  number={2},
  pages={1494},
  url={http://stacks.iop.org/0004-637X/691/i=2/a=1494},
  year={2009},
  abstract={A survey of the carbon chain negative ion C 6 H – and the structurally similar radicals C 4 H and C 6 H has been done with the 100 m Green Bank Telescope toward 24 galactic molecular sources. The most readily observed molecular anion to date, C 6 H – was detected in two new sources: the dark clouds L1544 and L1521F, where it was found to be present at the level of 2.5% ± 0.8% and 4% ± 1%, respectively relative to neutral C 6 H. C 4 H was detected in nearly all dark clouds surveyed (in six for the first time), and C 6 H was detected in five dark clouds and one translucent cloud. The observed C 6 H – /C 6 H (1%-4%) and C 6 H/C 4 H (0.2%-1%) ratios in these sources suggest that C 6 H – may be close to detection in many other dark clouds. The fractional ionization derived from the C 6 H – /C 6 H ratio in L1544 and L1521F of 10 –8 to 10 –7 is comparable to earlier estimates from positive molecular ions.}
}