Y. KASAI, National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795, Japan; E. KAGI, Faculty of Information Science, Hiroshima City University, Asaminami-ku, Hiroshima 731-3194, Japan; K. KAWAGUCHI, Department of Chemistry, Faculty of Science, Okayama University, Okayama 700-8530, Japan.

Existence of negative ions in space has been discussed for a long time. Although 13 positive ions have been known in interstellar space, the first identification of the negative ion C6H- was carried out quite recently by McCarthy et al.. In the present study, radio astronomical data of C6H- observed in a late tyep star IRC+10216 with Nobeyama 45-m and IRAM 30-m telescopes have been analyzed by the local thermodynamic equilibrium approximation to give the column density of 6.1-8.0 x 1012 cm-2 and the excitation temperature of 32 \pm 3 K with an assumed source size of 30" \pm 3". The abundance of C6H- was estimated to be 3.4 of C6H- and C6H indicate that the distribution of C6H- is in inner region of the circumstellar envelope than C6H. The production mechanism of C6H- is discussed.