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Título: The Unimolecular Chemistry of Methyl Chloroformate Ions and Neutrals : a Story of Near-Threshold Decomposition
Autor: Lowe, Bethany
Cardona, Alejandro L.
Bodi, Andras
Mayer, Paul M.
Burgos Paci, Maxi A.
Tipo: Artículo
Palabras clave: Methyl chloroformate, Imaging photoelectron photoion coincidence spectroscopy, Photoelectron spectroscopy, Pyrolysis, Reaction mechanisms, Computational chemistry, Kinetic modelling, Cloroformiato de metilo, Espectroscopia de coincidencia de fotoiones y fotoelectrones, Espectroscopia fotoelectrónica, Pirólisis, Mecanismos de reacción, Química computacional, Modelado cinético
Fecha de publicación: 2023
Resumen: The near threshold dissociation of ionized and neutral methyl chloroformate (CH3COOCl, MCF) was explored with imaging photoelectron photoion coincidence spectroscopy. The threshold photoelectron spectrum (TPES) for MCF was acquired for the first time; the large geometry changes upon ionization of MCF results in a broad, poorly defined TPES. Franck–Condon simulations are consistent with an adiabatic ionization energy (IE) of 10.90 ± 0.05 eV. Ionized MCF dissociates by chlorine atom loss at a measured 0 K appearance energy (AE) of 11.30 ± 0.01 eV. Together with the above IE, this AE suggests a reaction barrier of 0.40 ± 0.05 eV, consistent with the SVECV-f12 computational result of 0.41 eV. At higher internal energies, the loss of CH3O• becomes competitive due to its lower entropy of activation. Pyrolysis of neutral MCF formed the anticipated major products CH3Cl + CO2 (R1) and the minor products HCl + CO + CH2O (R2). The thermal decomposition products were identified by their photoion mass-selected threshold photoelectron spectrum (ms-TPES). Possible reaction pathways were explored computationally to confirm the dominant ones: R1 proceeds by a concerted Cl atom migration via a 4- membered transition state in agreement with the mechanism proposed in the literature. R2 is a twostep reaction first yielding 2-oxiranone by HCl loss, which then decomposes to CH2O and CO. Kinetic modeling of the neutral decomposition could simulate the observed reactions only if the vibrational temperature of the MCF was assumed not to cool in the expansion.
Descripción: Postprint
EN: Journal of the American Society for Mass Spectrometry, v.34, nº 12, 2023 --
Citación: Lowe, B, Cardona, A, Bodi, A,y otros. "The Unimolecular Chemistry of Methyl Chloroformate Ions and Neutrals : a Story of Near-Threshold Decomposition" Journal of the American Society for Mass Spectrometry [en línea] v.34, nº 12, 2023. 29 p. DOI: 10.1021/jasms.3c00334
Licencia: Licencia Creative Commons Atribución - No Comercial - Sin Derivadas (CC - By-NC-ND 4.0)
Aparece en las colecciones: Publicaciones académicas y científicas - Facultad de Química

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