Discovery of Methyl Acetate and Gauche Ethyl Formate in Orion

TL;DR

This paper reports the first detection of methyl acetate and gauche ethyl formate in the Orion region, providing insights into their formation mechanisms and physical conditions in space.

Contribution

It presents the first space detection of the gauche conformer of ethyl formate and detailed analysis of methyl acetate's rotational lines in Orion.

Findings

Methyl acetate mainly originates from the compact ridge region.

The rotational temperature of methyl acetate is approximately 150 K.

Both conformers of ethyl formate are detected with similar column densities.

Abstract

We report on the discovery of methyl acetate, CH3COOCH3, through the detection of a large number of rotational lines from each one of the spin states of the molecule: AA species (A1 or A2), EA species (E1), AE species (E2), EE species (E3 or E4). We also report the detection, for the first time in space, of the $gauche$ conformer of ethyl formate, CH3CH2OCOH, in the same source. The trans conformer is also detected for the first time outside the galactic center source SgrB2. From the derived velocity of the emission of methyl acetate we conclude that it arises mainly from the compact ridge region with a total column density of (4.2+-0.5)E15 cm(-2). The derived rotational temperature is 150 K. The column density for each conformer of ethyl formate, trans and gauche, is (4.5+-1.0)E14 cm(-2). Their abundance ratio indicates a kinetic temperature of 135 K for the emitting gas and suggests that gas phase reactions could participate efficiently in the formation of both conformers in addition to cold ice mantle reactions on the surface of dust grains.