Direct Observation of <i>para</i>-Xylylene as the Decomposition Product of the <i>meta</i>-Xylyl Radical Using VUV Synchrotron Radiation

Hemberger, Patrick; Trevitt, Adam J.; Ross, Ernest; Silva, Gabriel da

doi:10.1021/jz401207z

Cited by 58 publications

(66 citation statements)

References 33 publications

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“…So, the presence of o -xylylene, which has a lower ionization energy than p -xylylene, can be excluded at this position of the flame (6.5 mm). Similar observations were also made in a heated SiC reactor in previous work by Hemberger et al [14,15] , where different reactor temperatures showed different C 8 H 8 isomer compositions depending also on the prepared xylyl radical. The TPE spectrum of m/z = 104 obtained from pyrolysis of m -xylyl bromide at 1300 K surface temperature is also shown in Fig.…”

Section: Decomposition Of M -Xylenesupporting

confidence: 87%

“…The presence of benzocyclobutene indicates that this reaction also occurs here, although the o -xylylene could not be detected. Benzocyclobutene itself isomerizes to styrene [14,38] and was identified by the peak at 8.66 eV which matches the measured and calculated value of the adiabatic ionization energy of 8.65 eV [15] . Styrene can be found with the highest concentration of all C 8 H 8 isomers (the maximum mole fraction is twice that of pxylylene).…”

Section: Decomposition Of M -Xylenesupporting

confidence: 74%

“…m -Xylylene is in comparison to o -and p -xylylene a diradical and was not observed in our measurements or in [14][15][16] so that a rearrangement of the m -xylyl to the p -xylyl and the o -xylyl radical, respectively, must take place to obtain either p -xylylene [14] or styrene and benzocyclobutene. However, the o -xylyl radical was not found in the reaction zone of the fuel-rich flame (see Fig.…”

Section: Decomposition Of M -Xylenecontrasting

confidence: 55%

“…Finally, the mechanism of Gaïl and Dagaut [10] was developed from a previous reaction mechanism of the oxidation of p -xylene [9] and was also tested against low-pressure measurements. A rearrangement of the m -xylyl radical, which was observed in [14,15] and will be discussed later, is not included in any of the models. In [8,10,26] the isomerization is implied by considering the direct formation of p -xylylene from the m -xylyl radical ( m -CH 3 C 6 H 4 CH 2 = p -CH 2 C 6 H 4 CH 2 + H).…”

Section: Mole Fraction Profiles and Comparison To Kinetic Modeling Rementioning

confidence: 99%

“…Mouis et al [13] investigated the effect of m -xylene on soot in laminar ethylene co-flow diffusion flames from 1 to 5 atm. The pyrolysis of the xylyl radicals, as the first decomposition products of xylenes in combustion processes, was studied in detail experimentally by iPEPICO from the pyrolysis of xylyl bromides in a SiC reactor by Hemberger et al [14,15] and theoretically in [16,17] .…”

Section: Introductionmentioning

confidence: 99%

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Insights in m-xylene decomposition under fuel-rich conditions by imaging photoelectron photoion coincidence spectroscopy

Bierkandt

Hemberger

Oßwald

et al. 2017

Proceedings of the Combustion Institute

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A fuel-rich ( = 1.79) m -xylene flame (7.3% m -C 8 H 10 , 42.7% O 2 , 50.0% Ar) at low-pressure (40 mbar) was investigated with focus on the reactive fuel radicals (C 8 H 9 ) and the first decomposition steps leading to C 8 H 8 isomers. The results show that an isomerization of the m -xylyl radical to o -and p -xylyl must take place to explain the observed intermediates in agreement with pyrolysis experiments. Important higher polycyclic aromatic hydrocarbons (PAHs) relevant to soot formation were also identified. All Measurements were performed with a molecular-beam mass spectrometry (MBMS) setup at the Swiss Light Source (SLS), where single-photon ionization with VUV radiation offers soft ionization of the sampled species. Isomer-selective detection with unprecedented resolution is achieved by a combination of time-of-flight mass spectrometry and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. In principle, species can be identified by comparison of measured ionization efficiency (PIE) curves with known or calculated ionization energies of expected species. For convoluted signals of several species, this procedure works well for the isomer with the lowest ionization energy. Changes in the slopes of the ionization efficiency curve do not necessarily correlate with ionization thresholds of other isomers and the assignment of higher thresholds can become difficult. PEPICO spectrometry, which detects the electrons that are produced in the ionization process in coincidence with the ions, enables the measurement of mass-selected threshold photoelectron spectra (ms-TPES). These spectra improve the detection capability of isomers because vibrational transitions from the neutral into ionic states can be observed and used as a fingerprint of a specific molecule. The JID: PROCI [m; June 30, 2016;16:41 ] ms-TPES are compared with reference spectra from the literature or Franck-Condon simulations. Quantification of the major species as well as several intermediate species for this fuel-rich m -xylene flame yields a data set for model validation and experimental results are compared with five kinetic reaction models from the literature.

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Section: Decomposition Of M -Xylenesupporting

confidence: 87%

Section: Decomposition Of M -Xylenesupporting

confidence: 74%

Section: Decomposition Of M -Xylenecontrasting

confidence: 55%

Section: Mole Fraction Profiles and Comparison To Kinetic Modeling Rementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Insights in m-xylene decomposition under fuel-rich conditions by imaging photoelectron photoion coincidence spectroscopy

Bierkandt

Hemberger

Oßwald

et al. 2017

Proceedings of the Combustion Institute

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Photoionization and Pyrolysis of a 1,4‐Azaborinine: Retro‐Hydroboration in the Cation and Identification of Novel Organoboron Ring Systems

Holzmeier¹,

Lang²,

Hemberger³

et al. 2014

Chemistry A European J

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The photoionization and dissociative photoionization of 1,4-di-tert-butyl-1,4-azaborinine by means of synchrotron radiation and threshold photoelectron photoion coincidence spectroscopy is reported. The ionization energy of the compound was determined to be 7.89 eV. Several low-lying electronically excited states in the cation were identified. The various pathways for dissociative photoionization were modeled by statistical theory, and appearance energies AE0K were obtained. The loss of isobutene in a retro-hydroboration reaction is the dominant pathway, which proceeds with a reverse barrier. Pyrolysis of the parent compound in a chemical reactor leads to the generation of several yet unobserved boron compounds. The ionization energies of the C4 H6 BN isomers 1,2- and 1,4-dihydro-1,4-azaborinine and the C3 H6 BN isomer 1,2-dihydro-1,3-azaborole were determined from threshold photoelectron spectra.

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Elucidating the Thermal Decomposition of Dimethyl Methylphosphonate by Vacuum Ultraviolet (VUV) Photoionization: Pathways to the PO Radical, a Key Species in Flame‐Retardant Mechanisms

Liang

Hemberger

Neisius

et al. 2014

Chemistry A European J

117

109

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The production of phosphoryl species (PO, PO2, HOPO) is believed to be of great importance for efficient flame-retardant action in the gas phase. We present a detailed investigation of the thermal decomposition of dimethyl methylphosphonate (DMMP) probed by vacuum ultraviolet (VUV) synchrotron radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. This technique provides a snapshot of the thermolysis process and direct evidence of how the reactive phosphoryl species are generated during heat exposure. One of the key findings of this work is that only PO is formed in high concentration upon DMMP decomposition, whereas PO2 is absent. It can be concluded that the formation of PO2 needs an oxidative environment, which is typically the case in a real flame. Based on the identification of products such as methanol, formaldehyde, and PO, as well as the intermediates O=P-CH3, H2C=P-OH, and H2C=P(=O)H, supported by quantum chemical calculations, we were able to describe the predominant pathways that lead to active phosphoryl species during the thermal decomposition of DMMP.

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Direct Observation of para-Xylylene as the Decomposition Product of the meta-Xylyl Radical Using VUV Synchrotron Radiation

Cited by 58 publications

References 33 publications

Insights in m-xylene decomposition under fuel-rich conditions by imaging photoelectron photoion coincidence spectroscopy

Insights in m-xylene decomposition under fuel-rich conditions by imaging photoelectron photoion coincidence spectroscopy

Photoionization and Pyrolysis of a 1,4‐Azaborinine: Retro‐Hydroboration in the Cation and Identification of Novel Organoboron Ring Systems

Elucidating the Thermal Decomposition of Dimethyl Methylphosphonate by Vacuum Ultraviolet (VUV) Photoionization: Pathways to the PO Radical, a Key Species in Flame‐Retardant Mechanisms

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