Discovery of CHCHCCH and detection of HCCN, HCN, CHCHCN, and, tentatively, CHCHCCH in TMC-1.

We present the discovery in TMC-1 of vinyl acetylene, CHCHCCH, and the detection, for the first time in a cold dark cloud, of HCCN, HCN, and CHCHCN. A tentative detection of CHCHCCH is also reported. The column density of vinyl acetylene is (1.2±0.2)×10 cm, 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, CHCHCH. The column densities derived for HCCN and HCN are (4.4±0.4)×10 cm and (3.7±0.4)×10 cm, respectively. Hence, the HCCN/HCN abundance ratio is 1.2±0.3. For ethyl cyanide we derive a column density of (1.1 ±0.3)×10 cm. 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.