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

TL;DR

This study reports the discovery of vinyl acetylene and the first detection of several complex molecules in TMC-1, providing insights into cold dark cloud chemistry and molecular abundances.

Contribution

It presents the first detection of vinyl acetylene and several molecules in TMC-1, along with their quantified abundances and comparison with chemical models.

Findings

Vinyl acetylene is one of the most abundant hydrocarbons in TMC-1.

HCCN and HC4N have similar abundances with a ratio of 1.2.

Chemical models can explain the observed molecular abundances.

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)e13 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)e11 cm-2 and (3.7 +/- 0.4)e11 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)e11 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.