Deep K-band Observations of TMC-1 with the Green Bank Telescope: Detection of HC7O, Nondetection of HC11N, and a Search for New Organic Molecules

The 100 m Robert C. Byrd Green Bank Telescope K-band (KFPA) receiver was used to perform a high-sensitivity search for rotational emission lines from complex organic molecules in the cold interstellar medium toward TMC-1 (cyanopolyyne peak), focussing on the identification of new carbon-chain-bearing species as well as molecules of possible prebiotic relevance. We report a detection of the carbon-chain oxide species HC7O and derive a column density of (7.8 +/- 0.9) x 10(11) cm(-2). This species is theorized to form as a result of associative electron detachment reactions between oxygen atoms and C7H-, and/or reaction of C6H2+ with CO (followed by dissociative electron recombination). Upper limits are given for the related HC6O, C6O, and C7O molecules. In addition, we obtained the first detections of emission from individual C-13 isotopologues of HC7N, and derive abundance ratios HC7N/(HCCCCCCCN)-C-13 = 110 +/- 16 and HC7N/(HCCCCCCCN)-C-13 = 96 +/- 11, indicative of significant C-13 depletion in this species relative to the local interstellar elemental C-12/C-13 ratio of 60-70. The observed spectral region covered two transitions of HC11N, but emission from this species was not detected, and the corresponding column density upper limit is 7.4 x 10(10) cm(-2) (at 95% confidence). This is significantly lower than the value of 2.8 x 10(11) cm(-2) previously claimed by Bell et al. and confirms the recent nondetection of HC11N in TMC-1 by Loomis et al. Upper limits were also obtained for the column densities of malononitrile and the nitrogen heterocycles quinoline, isoquinoline, and pyrimidine.