Detection of C8H- and comparison with C8H toward IRC+10 216

We report the detection of new transitions of octatetraynyl (C8H) toward the circumstellar envelope IRC + 10 216 using data taken with the 100 m Green Bank Telescope ( GBT). In addition, we report five features from the Ku, K, and Q bands that have been identified as transitions of the octatetraynyl anion ( C8H-). From a rotational temperature diagram and an assumed source size of 30, we find a total C8H column density of cm 8(3) x 10(12) cm(-2) and a rotational temperature of similar to 13 K. From the five detected transitions of C8H-, we find a total C8H- column density of similar to 21 x 10(12) cm(-2) consistent with a rotational temperature of similar to 34 K for a total (CH)-H-8/(CH-)-H-8 column density ratio of similar to 3.8. This observed C8H/C8H- column density ratio is similar to the theoretical prediction of 3.6, while the observed column densities were lower than that predicted by a factor of similar to 30. This prompted us to reinvestigate the initial conditions of the circumstellar envelope (CSE) model. The new model results are presented, and they more closely match the C8H and C8H- abundances observed with the GBT. Finally, we use the new CSE model results to predict the abundance of decapentaynyl (C10H), and we compare them with the measured upper limit found from the GBT observations.