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Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory
Authors:Bethany Lowe  Alejandro L Cardona  Juana Salas  Andras Bodi  Paul M Mayer  Maxi A Burgos Paci
Institution:1. Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Canada;2. INFIQC – CONICET, Departamento fisicoquímica, Universidad Nacional de Córdoba, Córdoba, Argentina;3. Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, Villigen, Switzerland
Abstract:The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H2)–CH3 and trans (staggered) configuration of the O= C (H)– O – C (H2)– C H3 dihedral angles. We observed the following ethyl formate pyrolysis products: CH3CH2OH, CH3CHO, C2H6, C2H4, HC(O)OH, CH2O, CO2, and CO, with HC(O)OH and C2H4 pyrolyzing further, forming CO + H2O and C2H2 + H2. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH3CH2O + CHO and CH3CH2 + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.
Keywords:computational chemistry  ethyl formate  imaging photoelectron photoion coincidence spectroscopy  kinetic modeling  photoelectron spectroscopy  pyrolysis  reaction mechanisms
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