Dissociation of methyl formate (HCOOCH₃) molecules upon low-energy electron attachment

¹ Université de Lyon, Université Claude Bernard Lyon1, CNRS/IN2P3, UMR5822, Institut de Physique Nucléaire de Lyon, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne, France
² Marie Curie-Sklodowska University, Institute of Physics, Mass Spectrometry Department, Pl. M. C.-Sklodowskiej 1, 20-031, Lublin, Poland
e-mail: Andrzej.Pelc@poczta.umcs.lublin.pl
³ Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universität Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria
e-mail: Stephan.Denifl@uibk.ac.at

Received: 14 November 2017
Accepted: 25 April 2018

Abstract

Context. The methyl formate molecule (HCOOCH₃) is considered to be a key molecule in astrochemistry. The abundance of this molecule in space depends on the stability upon irradiation with particles like low-energy electrons.

Aims. We have investigated the decomposition of the molecule upon electron capture in the electron energy range from about 0 eV up to 15 eV. All experimentally obtained fragmentation channels of the molecular anion were investigated by quantum chemical calculations.

Methods. A high resolution electron monochromator coupled with quadrupole mass spectrometer was used for the present laboratory experiment. Quantum chemical calculations of the electron affinities of the generated fragments, the thermodynamic thresholds and the activation barriers for the associated reaction channels were carried out to complement the experimental studies.

Results. Electron attachment is shown to be a purely dissociative process for this molecule and proceeds within two electron energy regions of about 1 eV to 4 eV and from 5 eV to 14 eV. In our experiment five anionic fragments with m/z (and possible stoichiometric structure) 59 (C₂H₃O₂⁻), 58 (C₂H₂O₂⁻), 45 (CHO₂⁻) 31 (CH₃O⁻), and 29 (CHO⁻) were detected. The most abundant anion fragments that are formed through dissociative electron attachment to methyl formate are the complementary anions CH₃O⁻ and CHO⁻, associated with the same single bond cleavage and different survival probability.

Conclusions. The low-energy electron induced dissociation of methyl formate differs from its isomers acetic acid and glycolaldehyde, which leads to possible chemical selectivity in the chemical evolution.