Methyl formate synthesis via S\(\mathrm {_N}\)Acyl esterification on interstellar ice mantles

Abstract

Context

Methyl formate (MF) has been detected in several interstellar environments, but whether or not the formation of this molecule takes place in the gas phase or on the ices of interstellar grains is still unclear. In this study, we explore the synthesis of methyl formate through the nucleophilic acyl substitution (S\(_{\text {N}}\)Acyl) reaction between methanol (CH\(_{3}\)OH) and formic acid (HCOOH) on amorphous solid water, which is the main component of interstellar ice mantles.

Methods

Using density functional theory (DFT), we model MF formation by sampling HCOOH in different catalytic sites on the water clusters with CH\(_{3}\)OH, and vice versa, for initial reactant configurations. We select the initial binding modes from the binding energy distributions of both reactant species. We assess the energy and synchronicity of the reaction by analyzing the reaction mechanisms through intrinsic reaction coordinate (IRC) energy, reaction force, and reaction electronic flux profiles. Using Wiberg bond order derivatives, we identify reaction events linked to hidden transition states that are encountered along the reaction coordinate.