On the formation of deuterated methyl formate in hot corinos

Abstract

Methyl formate, HCOOCH3, 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 HCOOCH3 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 DCOOCH3 in the protostar IRAS 16293–2422. H-D substitution reactions on grains significantly enhance the abundances of HCOOCHD2, DCOOCHD2, and HCOOCD3. The observed abundance of HCOOCHD2 in IRAS 16293–2422 can only be reproduced if H-D substitution reactions are taken into account. However, HCOOCH2D 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.