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Robertson NK, Onel L, Blitz MA, Shannon R, Stone D, Seakins PW, Robertson SH, Kühn C, Pazdera TM, Olzmann M. Temperature-Dependent, Site-Specific Rate Coefficients for the Reaction of OH (OD) with Methyl Formate Isotopologues via Experimental and Theoretical Studies. J Phys Chem A 2024; 128:5028-5040. [PMID: 38885649 PMCID: PMC11215782 DOI: 10.1021/acs.jpca.4c02524] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Revised: 05/30/2024] [Accepted: 05/30/2024] [Indexed: 06/20/2024]
Abstract
Methyl esters are an important component of combustion and atmospheric systems. Reaction with the OH radical plays an important role in the removal of the simplest methyl ester, methyl formate (MF, CH3OCHO). In this paper, the overall rate coefficients for the reactions of OH and OD with MF isotopologues, studied under pseudo-first-order conditions, are reported using two different laser flash photolysis systems with the decay of OH monitored by laser-induced fluorescence. The room-temperature rate coefficient for OH + MF, (1.95 ± 0.34) × 10-13 cm3 molecule-1 s-1, is in good agreement with the literature. The rate coefficient exhibits curved Arrhenius behavior, and our results bridge the gap between previous low-temperature and shock tube studies. In combination with the literature, the rate coefficient for the reaction of OH with MF between 230 and 1400 K can be parametrized as kOH+MF = (3.2 × 10-13) × (T/300 K)2.3 × exp(-141.4 K/T) cm3 molecule-1 s-1 with an overall estimated uncertainty of ∼30%. The reactions of OD with MF isotopologues show a small enhancement (inverse secondary isotope effect) compared to the respective OH reactions. The reaction of OH/OD with MF shows a normal primary isotope effect, a decrease in the rate coefficient when MF is partially or fully deuterated. Experimental studies have been supported by ab initio calculations at the CCSD(T)-F12/aug-cc-pVTZ//M06-2X/6-31+G** level of theory. The calculated, zero-point-corrected, barrier heights for abstraction at the methyl and formate sites are 1.3 and 6.0 kJ mol-1, respectively, and the ab initio predictions of kinetic isotope effects are in agreement with experiment. Fitting the experimental isotopologue data refines these barriers to 0.9 ± 0.6 and 4.1 ± 0.9 kJ mol-1. The branching ratio is approximately 50:50 at 300 K. Between 300 and 500 K, abstraction via the higher-energy, higher-entropy formate transition state becomes more favored (60:40). However, experiment and calculations suggest that as the temperature increases further, with higher energy, less constrained conformers of the methyl transition state become more significant. The implications of the experimental and theoretical results for the mechanisms of MF atmospheric oxidation and low-temperature combustion are discussed.
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Affiliation(s)
| | - Lavinia Onel
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
| | - Mark A. Blitz
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
- National
Centre for Atmospheric Science, University
of Leeds, Leeds LS2 9JT, U.K.
| | - Robin Shannon
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
| | - Daniel Stone
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
| | - Paul W. Seakins
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
| | | | - Christian Kühn
- Institut
für Physikalische Chemie, Karlsruher
Institut für Technologie (KIT), 76131 Karlsruhe, Germany
| | - Tobias M. Pazdera
- Institut
für Physikalische Chemie, Karlsruher
Institut für Technologie (KIT), 76131 Karlsruhe, Germany
| | - Matthias Olzmann
- Institut
für Physikalische Chemie, Karlsruher
Institut für Technologie (KIT), 76131 Karlsruhe, Germany
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Vallance C, Orr-Ewing AJ. Virtual Issue on Photodissociation: From Fundamental Dynamics and Spectroscopy to Photochemistry in Planetary Atmospheres and in Space. J Phys Chem A 2023; 127:5767-5771. [PMID: 37469270 DOI: 10.1021/acs.jpca.3c03975] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/21/2023]
Affiliation(s)
- Claire Vallance
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Andrew J Orr-Ewing
- School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom
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Yuan Y, Tsai P. Photodissociation dynamics of acetaldehyde at 267 nm: A computational study of the
CO
‐forming channels. J CHIN CHEM SOC-TAIP 2023. [DOI: 10.1002/jccs.202300036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
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Wenz J, Pazdera TM, Golka L, Olzmann M. Pyrolysis of Methyl Formate and the Reaction of Methyl Formate with H Atoms: Shock Tube Experiments and Statistical Rate Theory. J Phys Chem A 2023; 127:1036-1045. [PMID: 36683280 DOI: 10.1021/acs.jpca.2c07053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Methyl formate (MF) is the smallest carboxylic ester and currently considered a promising alternative fuel. It can also serve as a model compound to study the combustion chemistry of the ester group, which is a typical structural feature in many biodiesel components. In the present work, the pyrolysis of MF was investigated behind reflected shock waves at temperatures between 1430 and 2070 K at a nominal pressure of 1.1 bar. Both time-resolved hydrogen atom resonance absorption spectroscopy (H-ARAS) and time-resolved time-of-flight mass spectrometry (TOF-MS) were used for species detection. Additionally, the reaction of MF and perdeuterated MF-d4 with H atoms was investigated at temperatures between 1000 and 1300 K at nominal pressures of 0.4 and 1.1 bar with H-ARAS. In the latter experiments, ethyl iodide served as precursor for H atoms. Rate coefficients of seven parallel unimolecular decomposition channels of MF and five parallel reaction channels of the MF + H reaction were calculated from statistical rate theory on the basis of molecular and transition state data from quantum chemical calculations. These calculated rate coefficients were implemented into an MF pyrolysis/oxidation mechanism from the literature, and the experimental concentration-time profiles of H (from ARAS) as well as MF, CH3OH, HCHO, and CO (from TOF-MS) were modeled. It turned out that the literature mechanism, which was originally validated against flow-reactor experiments, ignition delay times, and laminar burning velocities, was generally able to fit also the concentration-time profiles from the shock tube experiments reasonably well. The agreement could still be improved by substituting the original rate coefficients, which were estimated from structure-reactivity relationships, by the values calculated from statistical rate theory in the present work. Details of the channel branching are discussed, and the updated mechanism is given, also in machine-readable form.
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Affiliation(s)
- Johannes Wenz
- Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
| | - Tobias M Pazdera
- Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
| | - Leonie Golka
- Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
| | - Matthias Olzmann
- Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
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5
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Tsai PY, Palazzetti F. Photodissociation dynamics of CO-forming channel of methyl formate at 193 nm: a computational study. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1977405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Po-Yu Tsai
- Department of Chemistry, National Chung Hsing University, Taichung, Taiwan
| | - Federico Palazzetti
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
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