title: Detection and Identification of the Keto-Hydroperoxide (HOOCH2OCHO) and Other Intermediates during Low-Temperature Oxidation of Dimethyl Ether.
abstract: In this paper we report the detection and identification of the keto-hydroperoxide (hydroperoxymethyl formate, HPMF, HOOCH2OCHO) and other partially oxidized intermediate species arising from the low-temperature (540 K) oxidation of dimethyl ether (DME). These observations were made possible by coupling a jet-stirred reactor with molecular-beam sampling capabilities, operated near atmospheric pressure, to a reflectron time-of-flight mass spectrometer that employs single-photon ionization via tunable synchrotron-generated vacuum-ultraviolet radiation. On the basis of experimentally observed ionization thresholds and fragmentation appearance energies, interpreted with the aid of ab initio calculations, we have identified HPMF and its conceivable decomposition products HC(O)O(O)CH (formic acid anhydride), HC(O)OOH (performic acid), and HOC(O)OH (carbonic acid). Other intermediates that were detected and identified include HC(O)OCH3 (methyl formate), cycl-CH2-O-CH2-O- (1,3-dioxetane), CH3OOH (methyl hydroperoxide), HC(O)OH (formic acid), and H2O2 (hydrogen peroxide). We show that the theoretical characterization of multiple conformeric structures of some intermediates is required when interpreting the experimentally observed ionization thresholds, and a simple method is presented for estimating the importance of multiple conformers at the estimated temperature (∼100 K) of the present molecular beam. We also discuss possible formation pathways of the detected species: for example, supported by potential energy surface calculations, we show that performic acid may be a minor channel of the O2 + ĊH2OCH2OOH reaction, resulting from the decomposition of the HOOCH2OĊHOOH intermediate, which predominantly leads to the HPMF.
authors.affiliation: †Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States.|‡Department of Chemistry, Bielefeld University, D-33615 Bielefeld, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Moshammer
authors.affiliation: †Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States.
authors.forename: Ahren W
authors.initials: AW
authors.lastname: Jasper
authors.affiliation: §Departments of Chemistry and Physics, University of California, Berkeley, California 94720, United States.|∥Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors.forename: Denisia M
authors.initials: DM
authors.lastname: Popolan-Vaida
authors.affiliation: †Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States.
authors.forename: Arnas
authors.initials: A
authors.lastname: Lucassen
authors.affiliation: ⊥Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Pascal
authors.initials: P
authors.lastname: Diévart
authors.affiliation: #Clean Combustion Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
authors.forename: Hatem
authors.initials: H
authors.lastname: Selim
authors.affiliation: †Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States.
authors.forename: Arkke J
authors.initials: AJ
authors.lastname: Eskola
authors.affiliation: †Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Taatjes
authors.affiliation: §Departments of Chemistry and Physics, University of California, Berkeley, California 94720, United States.|∥Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Leone
authors.affiliation: #Clean Combustion Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
authors.forename: S Mani
authors.initials: SM
authors.lastname: Sarathy
authors.affiliation: ⊥Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Yiguang
authors.initials: Y
authors.lastname: Ju
authors.affiliation: ∇Centre National de la Recherche Scientifique (CNRS), INSIS, 45071 Orléans Cedex 2, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Dagaut
authors.affiliation: ‡Department of Chemistry, Bielefeld University, D-33615 Bielefeld, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Kohse-Höinghaus
authors.affiliation: †Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States.
authors.forename: Nils
authors.initials: N
authors.lastname: Hansen