SIMBAD references

A survey of the carbon chain negative ion C₆H^– and the structurally similar radicals C₄ H and C₆H has been done with the 100 m Green Bank Telescope toward 24 galactic molecular sources. The most readily observed molecular anion to date, C₆H^– 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 C₆H. C₄ H was detected in nearly all dark clouds surveyed (in six for the first time), and C₆ H was detected in five dark clouds and one translucent cloud. The observed C₆H^–/C₆ H (1%-4%) and C₆H/C₄H (0.2%-1%) ratios in these sources suggest that C₆H^– may be close to detection in many other dark clouds. The fractional ionization derived from the C₆H^–/C₆ H ratio in L1544 and L1521F of 10^–8 to 10^–7 is comparable to earlier estimates from positive molecular ions.