Modelling of c-C2H4O formation on grain surfaces

TL;DR

This paper develops a chemical model incorporating recent experimental data to explain the formation and observed abundance of ethylene oxide on grain surfaces in interstellar dense cores, highlighting its formation during cold phases and release in hot cores.

Contribution

It introduces a new chemical model that includes recent experimental findings on ethylene oxide formation on grain surfaces, improving understanding of its abundance in star-forming regions.

Findings

Ethylene oxide can form during the cold phase of dense cores.

The model reproduces observed ethylene oxide abundances in star-forming regions.

Ethylene oxide is released during the hot core phase via thermal desorption.

Abstract

Despite its potential reactivity due to ring strain, ethylene oxide (c-C2H4O) is a complex molecule that seems to be stable under the physical conditions of an interstellar dense core; indeed it has been detected towards several high-mass star forming regions with a column density of the order of 10e13cm-2 (Ikeda et al. 2001). To date, its observational abundances cannot be reproduced by chemical models and this may be due to the significant contribution played by its chemistry on grain surfaces. Recently, Ward and Price (2011) have performed experiments in order to investigate the surface formation of ethylene oxide starting with oxygen atoms and ethylene ice as reactants. We present a chemical model which includes the most recent experimental results from Ward and Price (2011) on the formation of c-C2H4O. We study the influence of the physical parameters of dense cores on the abundances of c-C2H4O. We verify that ethylene oxide can indeed be formed during the cold phase (when the ISM dense cores are formed), via addition of an oxygen atom across the C=C double bond of the ethylene molecule, and released by thermal desorption during the hot core phase. A qualitative comparison between our theoretical results and those from the observations shows that we are able to reproduce the abundances of ethylene oxide towards high-mass star-forming regions.