A proposed chemical scheme for HCCO formation in cold dense clouds

TL;DR

This paper introduces a new chemical scheme that successfully models the formation of HCCO in cold dense clouds, aligning with recent observations by proposing a significantly increased reaction rate for a key formation pathway.

Contribution

It presents a novel chemical network with an enhanced reaction rate for OH + CCH, enabling accurate reproduction of HCCO abundances in dark clouds.

Findings

The proposed scheme reproduces observed HCCO levels in Lupus-1A and L486.

A larger rate coefficient for OH + CCH is essential for matching observations.

The scheme also accounts for HCO, H2CCO, and CH3CHO abundances.

Abstract

The ketenyl radical (HCCO) has recently been discovered in two cold dense clouds with a non-negligible abundance of a few 1e-11 (compared to H2) (Agundez et al. 2015). Until now, no chemical network has been able to reproduce this observation. We propose here a chemical scheme that can reproduce HCCO abundances together with HCO, H2CCO and CH3CHO in the dark clouds Lupus-1A and L486. The main formation pathway for HCCO is the OH + CCH -> HCCO + H reaction as suggested by Agundez et al. (2015) but with a much larger rate coefficient than used in current models. Since this reaction has never been studied experimentally or theoretically, this larger value is based on a comparison with other similar systems.