The first discovered negative molecular ion, C 6 H - M. C. McCarthy et al, ApJ, 652:L 吳宇智 (Yu-chih, Wu) Department of Physics, NTHU 12,19,2006

No negative ions? Nearly 130 neutral molecules and 14 positive molecular ions have been found in interstellar space. Negative ions are rare because ultraviolet light that suffuses space easily knocks electrons off molecules.

Hexatriyne anion C 6 H - High electron binding enegy(3.8eV), closed-shell electronic ground state, large size, large dipole moment

Laboratory observation Rotational spectrum of C 6 H - in the radio band: 17 lines between 8 and 187 GHz Instrument: free-space millimeter-wave spectrometer

Astronomical observation Two sources are observed this series of lines: the molecular shell of the red giant star IRC (Kawaguchi et al), and the dense molecular cloud TMC-1 (Green Bank Telescope).

Identification 7 lines in IRC lines in TMC-1 Rotational constant B: laboratory: (7) astronomical: (294)

More negative ions? The density of C 6 H - is 1%~5% that of neutral C 6 H. If other molecular anions are similarly abundant relative to their neutral counterparts, they should be detectable both in the laboratory at high resolution and in astronomical sources.