Detection of the Carbon Chain Negative Ion C8H- in TMC-1

The negative molecular ion C₈H^- has been detected in the Galactic molecular source TMC-1. Four rotational transitions have been observed in the centimeter-wave band with the NRAO 100 m Green Bank Telescope (GBT) at precisely the frequencies calculated from the recent laboratory spectroscopy of this large carbon chain anion. C₈H^- is about 5% as abundant as C₈H, or somewhat more than C₆H^- relative to C₆H (1.6%). Improved values of the column densities of C₆H^- and C₆H, and an upper limit for the abundance of the smaller carbon chain C₄H^- of 0.014% with respect to C₄H, have also been determined.