| Abstract
| - We present the discovery in TMC-1 of vinyl acetylene, CH 2CHCCH, and the detection, for the first time in a cold dark cloud, of HCCN, HC 4N, and CH 3CH 2CN. A tentative detection of CH 3CH 2CCH is also reported. The column density of vinyl acetylene is (1.2 ± 0.2) × 10 13 cm −2, which makes it one of the most abundant closed-shell hydrocarbons detected in TMC-1. Its abundance is only three times lower than that of propylene, CH 3CHCH 2. The column densities derived for HCCN and HC 4N are (4.4 ± 04) × 10 11 cm −2 and (3.7 ± 0.4) × 10 11 cm −2, respectively. Hence, the HCCN/HC 4N abundance ratio is 1.2 ± 0.3. For ethyl cyanide we derive a column density of (1.1 ± 0.3) × 10 11 cm −2. These results are compared with a state-of-the-art chemical model of TMC-1, which is able to account for the observed abundances of these molecules through gas-phase chemical routes.
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