The multiplexed chemical kinetic photoionization mass spectrometer: A new approach to isomer-resolved chemical kinetics

The CH(X2Π) + propene reaction is studied in the gas phase at 298 K and 4 Torr (533.3 Pa) using VUV synchrotron photoionization mass spectrometry. The dominant product channel is the formation of C4H6 (m/z 54) + H. By fitting experimental photoionization spectra to measured spectra of known C4H6 isomers, the following relative branching fractions are obtained: 1,3-butadiene (0.63 ± 0.13), 1,2-butadiene (0.25 ± 0.05), and 1-butyne (0.12 ± 0.03) with no detectable contribution from 2-butyne. The CD + propene reaction is also studied and two product channels are observed that correspond to C4H6 (m/z 54) + D and C4H5D (m/z 55) + H, formed at a ratio of 0.4 (m/z 54) to 1.0 (m/z 55). The D elimination channel forms almost exclusively 1,2-butadiene (0.97 ± 0.20) whereas the H elimination channel leads to the formation of deuterated 1,3-butadiene (0.89 ± 0.18) and 1-butyne (0.11 ± 0.02); photoionization spectra of undeuterated species are used in the fitting of the measured m/z 55 (C4H5D) spectrum. The results are generally consistent with a CH cycloaddition mechanism to the C═C bond of propene, forming 1-methylallyl followed by elimination of a H atom via several competing processes. The direct detection of 1,3-butadiene as a reaction product is an important validation of molecular weight growth schemes implicating the CH + propene reaction, for example, those reported recently for the formation of benzene in the interstellar medium ( Jones, B. M. Proc. Natl. Acad. Sci. U.S. A. 2011, 108, 452−457 ABSTRACTThe CH (X 2 Π) + propene reaction is studied in the gas phase at 298 K and 4 Torr (533.3 Pa) using VUV synchrotron photoionization mass spectrometry. The dominant product channel is the formation of C 4 H 6 (m/z 54) + H. By fitting experimental photoionization spectra to measured spectra of known C 4 H 6 isomers, the following relative branching fractions are obtained: 1,3-butadiene (0.63 ± 0.13), 1,2-butadiene (0.25 ± 0.05) and 1-butyne (0.12 ± 0.03) with no detectable contribution from 2-butyne. The CD + propene reaction is also studied and two product channels are observed that correspond to 2011, 108, 452-457).KEYWORDS: radical, gas-phase, photoionization, synchrotron, propene, methylidyne, mass spectrometry. 3 INTRODUCTIONThe highly reactive methylidyne (CH) radical affects the chemistry of energetic gasphase environments including combustion 1-3 , interplanetary atmospheres 4-6 and the interstellar medium. 7 In order to accurately model these systems, detailed chemical data are needed in the form of reaction rate coefficients and product branching fractions. Our purpose here is to determine total product branching fractions and provide mechanistic details for the CH (X 2 Π) + propene reaction. The present work builds on a series of previous product detection studies of the CH radical with small, unsaturated hydrocarbons: acetylene (C 2 H 2 ), ethylene (C 2 H 4 ), allene (C 3 H 4 , CH 2 CCH 2 ) and propyne (C 3 H 4 , CH 3 CCH). 8 Recent works have also investigated the CH reaction with the carbonyl-conta...

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“…11,17,18 The experiment comprises a reaction flow tube coupled to a photoionization mass spectrometer.…”

Section: Experimental Methodsmentioning

confidence: 99%

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

et al. 2013

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“…22 The experimental setup, 22 inspired by the general PIMS design of Slagle and Gutman, 23 has been described in previous studies [24][25][26] and only a brief overview will be given here. Typically, the gas flow consists of small amounts of the radical precursor (CHBr 3 , 2.0 x 10 13 cm -3 ) and the reactant (pyrrole, 5.0 x 10 14 cm -3 ) in helium carrier gas.…”

Section: Experimental Apparatusmentioning

confidence: 99%

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

Soorkia

Taatjes

Osborn

et al. 2010

Phys. Chem. Chem. Phys.

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“…50 The Multiplexed Photoionization Mass Spectrometer building upon the general PIMS design of Slagle and Gutman, 51 has been described in previous studies 17, 50,52 and only a brief overview will be given here. The instrument has benefitted from a recent major upgrade: the magnetic sector mass spectrometer described previously has been replaced by an orthogonal accelerated time-of-flight (OA-TOF) mass spectrometer with a superior mass resolution of ~2000.…”

Section: Photoionization Mass Spectrometry (Pims)mentioning

confidence: 99%

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection

Soorkia

Trevitt

Selby³

et al. 2010

J. Phys. Chem. A

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The rate coefficient for the reaction of the ethynyl radical (C 2 H) with 1-butyne (H-C≡C-CH 2 -CH 3 ) is measured in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by laser photolysis of acetylene (C 2 H 2 ) at 193 nm and detected via chemiluminescence (C 2 H + O 2 → CH (A 2 Δ) + CO 2 ). The rate coefficients are measured over the temperature range of 74-295 K. The C 2 H + 1-butyne reaction exhibits no barrier and occurs with rate constants close to the collision limit. The temperature dependent rate coefficients can be fit within experimental uncertainties by the expression k = (2.4 ± 0.5) × 10 -10 (T/295 K) -(0.04 ± 0.03) cm 3 molecule -1 s -1 . Reaction products are detected at room temperature (295 K) and 533 Pa using a Multiplexed Photoionization Mass Spectrometer (MPIMS) coupled to the tunable VUV synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory. Two product channels are identified for this reaction: m/z = 64 (C 5 H 4 ) and m/z = 78 (C 6 H 6 ) corresponding to the CH 3 -and H-loss channels, respectively. Photoionization efficiency (PIE) curves are used to analyze the isomeric composition of both product channels. The C 5 H 4 products are found to be exclusively linear isomers composed of ethynylallene and methyldiacetylene in a 4:1 ratio. In contrast, the C 6 H 6 product channel includes two cyclic isomers, fulvene 18(±5)% and 3,4-dimethylenecyclobut-1-ene 32(±8)%, as well as three linear isomers, 2-ethynyl-1,3-butadiene 8(±5)%, 3,4-hexadiene-1-yne 28(±8)% and 1,3-hexadiyne 14(±5)%. Within experimental uncertainties, we do not see appreciable amounts of benzene and an upper limit of 10 % is estimated. Diacetylene (C 4 H 2 ) formation via the C 2 H 5 -loss channel is also thermodynamically possible but cannot be observed due to experimental limitations. The implications of these results for modeling of planetary atmospheres, especially of Saturn's largest moon Titan, are discussed.

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The multiplexed chemical kinetic photoionization mass spectrometer: A new approach to isomer-resolved chemical kinetics

Cited by 197 publications

References 27 publications

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection

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The multiplexed chemical kinetic photoionization mass spectrometer: A new approach to isomer-resolved chemical kinetics

Cited by 197 publications

References 27 publications

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

Reaction of the C2H Radical with 1-Butyne (C4H6): Low-Temperature Kinetics and Isomer-Specific Product Detection

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Reaction of the C₂H Radical with 1-Butyne (C₄H₆): Low-Temperature Kinetics and Isomer-Specific Product Detection