Discovery of CH2CHCCH and detection of HCCN, HC4N, CH3CH2CN, and, tentatively, CH3CH2CCH in TMC-1

Abstract

We present the discovery in TMC-1 of vinyl acetylene, CH₂CHCCH, and the detection, for the first time in a cold dark cloud, of HCCN, HC₄N, and CH₃CH₂CN. A tentative detection of CH₃CH₂CCH is also reported. The column density of vinyl acetylene is (1.2±0.2)×10¹³ 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, CH₃CHCH₂. The column densities derived for HCCN and HC₄N are (4.4±0.4)×10¹¹ cm^-2 and (3.7±0.4)×10¹¹ cm^-2, respectively. Hence, the HCCN/HC₄N abundance ratio is 1.2±0.3. For ethyl cyanide we derive a column density of (1.1 ±0.3)×10¹¹ 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.

Keywords: ISM: individual (TMC-1); ISM: molecules; astrochemistry; line: identification; molecular data.