Methyl Acetate and Its Singly Deuterated Isotopomers in the Interstellar Medium

Abstract

Methyl acetate (CH 3 COOCH 3 ) has been recently observed by IRAM 30 m radio telescope in Orion though the presence of its deuterated isotopomers is yet to be confirmed. We therefore study the properties of various forms of methyl acetate, namely, CH 3 COOCH 3 , CH 2 DCOOCH 3 and CH 3 COOCH 2 D. Our simulation reveals that these species could be produced efficiently both in gas as well as in ice phases. Production of methyl acetate could follow radical-radical reaction between acetyl (CH 3 CO) and methoxy (CH 3 O) radicals. To predict abundances of CH 3 COOCH 3 along with its two singly deuterated isotopomers and its two isomers (ethyl formate and hydroxyacetone), we prepare a gasgrain chemical network to study chemical evolution of these molecules. Since gas phase rate coefficients for methyl acetate and its related species were unknown, either we consider similar rate coefficients for similar types of reactions (by following existing data bases) or we carry out quantum chemical calculations to estimate the unknown rate coefficients. For the surface reactions, we use adsorption energies of reactants from some earlier studies. Moreover, we perform quantum chemical calculations to obtain spectral properties of methyl acetate in infrared and sub-millimeter regions. We prepare two catalog files for the rotational transitions of CH 2 DCOOCH 3 and CH 3 COOCH 2 D in JPL format, which could be useful for their detection in regions of interstellar media where CH 3 COOCH 3 has already been observed.

Gas-phase kinetics of CH3CHO with OH radicals between 11.7 and 177.5 K

“…Although not yet detected in the ISM, Das et al 26 proposed that CH 3 CO can be involved in the formation of methyl acetate (CH 3 OC(O)CH 3 ) in the ISM. Other authors proposed that CH 3 CHO and CH 3 CO can be involved in grain surface, 27 , 28 bimolecular, [29][30][31] and even termolecular 30 processes at temperatures between 10 and 200 K in the ISM or in planetary atmospheres.…”

Effect of Binding Energies on the Encounter Desorption

“…We have included the encounter desorption phenomenon in our CMMC code (Das et al, 2015a;Das et al, 2015b;Das et al, 2016;Gorai et al, 2017a;Gorai et al, 2017b;Sil et al, 2018;Gorai et al, 2020b) to study its effect. The surface chemistry network of our model is mostly adopted from Ruaud et al (2015), Das et al (2015b), and Gorai et al (2020b).…”

“…Here, we employ quantum chemical calculations to determine the adsorption energy of these species with H 2 molecule. Obtained BE assessments are executed in our Chemical Model of Molecular Cloud (hereafter CMMC) (Das et al, 2015a;Das et al, 2015b;Gorai et al, 2017a;Gorai et al, 2017b;Sil et al, 2018;Gorai et al, 2020b). The encounter desorption effect is vital during the prestellar core phase.…”

Radiative transfer modeling of the observed line profiles in G31.41+0.31

“…Detailed chemical modeling has been carried out to study the abundances of the species observed in G31. Our Chemical Model for Molecular Cloud (CMMC) (Das et al, 2015a(Das et al, ,b, 2016Gorai et al, 2017a,b;Sil et al, 2018;Gorai et al, 2020;Sil et al, 2021;Das et al, 2021) is considered for this modeling. 2013) and infall velocity variation is derived from the Equation 1 by using v 1000 = 4.9 km s −1 .…”