The largest anion identified to date in space is C8H–, which goes
by the formal (and tongue twisting) name octatetraynyl anion. The
detection was reported in 2007 by
three groups, initially in back-to-back ApJL papers by
Brünken et al. and
Remijan et al., followed within a few months by
confirming observations reported by
Kawaguchi et al. The detection of Brünken et al.
TMC-1 while that of Remijan et al. was toward
IRC+10216; both groups used data collected with the 100m
Robert C. Bird Green Bank Telescope.
The detection of Kawaguchi et al. was also toward IRC +10216 based on observations with the 45m telescope at
Nobeyama Radio Observatory.
A total of 13 different transitions were observed by the three efforts. The detection was made possible
by laboratory measurement of the rotational spectrum of C8H– by
Gupta et al.
To date five anions have been detected in space in the gas phase. In addition to
C8H–, the detections of the
hexatriynyl (C6H–) and
butadiynyl (C4H–) anions
were both reported in 2007, while the detections of the
cyanoethynyl (C3N–) and
cyanobutadiynyl (C5N–) anions
were reported in 2008, and the detection of the
cyano (CN–) anion was reported in 2010.