On the Formation of Deuterated Methyl Formate in Hot Corinos

TL;DR

This study investigates the formation pathways of deuterated methyl formate in star-forming regions using chemical modeling, highlighting the importance of radical reactions and H-D substitution, but also revealing complexities in deuteration processes.

Contribution

It provides the first detailed theoretical analysis of deuterated methyl formate formation, emphasizing the role of radical-radical reactions and H-D substitution on grains.

Findings

Radical-radical association on grains explains DCOOCH3 abundance.

H-D substitution reactions significantly increase deuterated methyl formate species.

Models underestimate HCOOCH2D, indicating more complex deuteration mechanisms.

Abstract

Methyl formate, HCOOCH$_3$, and many of its isotopologues have been detected in astrophysical regions with considerable abundances. However, the recipe for the formation of this molecule and its isotopologues is not yet known. In this work, we attempt to investigate, theoretically, the successful recipe for the formation of interstellar HCOOCH$_3$ and its deuterated isotopologues. We used the gas-grain chemical model, UCLCHEM, to examine the possible routes of formation of methyl formate on grain surfaces and in the gas-phase in low-mass star-forming regions. Our models show that radical-radical association on grains are necessary to explain the observed abundance of DCOOCH$_3$ in the protostar IRAS~16293--2422. H-D substitution reactions on grains significantly enhance the abundances of HCOOCHD$_2$, DCOOCHD$_2$, and HCOOCD$_3$. The observed abundance of HCOOCHD$_2$ in IRAS 16293--2422 can only be reproduced if H-D substitution reactions are taken into account. However, HCOOCH$_2$D remain underestimated in all of our models. The deuteration of methyl formate appears to be more complex than initially thought. Additional studies, both experimentally and theoretically, are needed for a better understanding of the interstellar formation of these species.