Chemical dynamics, molecular energetics, and kinetics at the synchrotron

Leone, Stephen R.; Ahmed, Musahid; Wilson, Kevin R.

doi:10.1039/c001707h

Cited by 75 publications

(64 citation statements)

References 86 publications

(121 reference statements)

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“…Within the last two decades, synchrotron radiation sources have been coupled to CMB, [36][37][38] various pyrolysis sources, reactors and flames. 25,[39][40][41][42][43] The Advanced Light Source (LBNL, USA) 1.9 GeV synchrotron is equipped with an undulator-based VUV beamline that provides photons ranging from ∼ 7.0 eV up to 14 eV with an energy resolution of ~ 5 -25 meV. 26,40 This energy range covers ionization thresholds for a vast number of organic molecules and radical species.…”

Section: Introductionmentioning

confidence: 99%

“…25,[39][40][41][42][43] The Advanced Light Source (LBNL, USA) 1.9 GeV synchrotron is equipped with an undulator-based VUV beamline that provides photons ranging from ∼ 7.0 eV up to 14 eV with an energy resolution of ~ 5 -25 meV. 26,40 This energy range covers ionization thresholds for a vast number of organic molecules and radical species. For detecting isomer products from a gaseous source, photoion mass spectra are recorded while stepping the energy of the incident photons.…”

Section: Introductionmentioning

confidence: 99%

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Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

Trevitt

Goulay

2016

Phys. Chem. Chem. Phys.

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For reactive gas-phase environments, including combustion, extraterrestrials atmospheres and our Earth's atmosphere, the availability of quality chemical data is essential for predictive chemical models. These data include reaction rate coefficients and product branching fractions. This perspective overviews recent isomerresolved production detection experiments for reactions of two of the most reactive gas phase radicals, the CN and CH radicals, with a suite of small hydrocarbons. A particular focus is given to flow-tube experiments using synchrotron photoionization mass spectrometry. Coupled with computational studies and other experiment techniques, flow tube isomer-resolved product detection have provided significant mechanistic details of these radical + neutral reactions with some general patterns emerging. Disciplines Medicine and Health Sciences | Social and Behavioral Sciences ABSTRACTFor reactive gas-phase environments, including combustion, extraterrestrials atmospheres and our Earth's atmosphere, the availability of quality chemical data is essential for predictive chemical models. These data include reaction rate coefficients and product branching fractions. This perspective overviews recent isomer-resolved production detection experiments for reactions of two of the most reactive gas phase radicals, the CN and CH radicals, with a suite of small hydrocarbons. A particular focus is given to flowtube experiments using synchrotron photoionization mass spectrometry. Coupled with computational studies and other experiment techniques, flow tube isomer-resolved product detection have provided significant mechanistic details of these radical + neutral reactions with some general patterns emerging.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

Trevitt

Goulay

2016

Phys. Chem. Chem. Phys.

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“…Molecular ions observed in VUV-AMS spectra of unoxidized and slightly oxidized squalane have been successfully used to obtain chemical and mechanistic insight into the squalane oxidation reaction . Moreover, the tunability of the VUV light can be used to investigate the chemical identity of species by measuring their threshold ionization energy (Leone et al, 2010). The threshold ionization energy of most organic molecules is 10.5 eV and those of H 2 O, CO 2 , and CO molecules are 12.62, 13.77, and 14.01 eV, respectively (NIST Chemistry WebBook: http://webbook.nist.gov/chemistry/).…”

Section: Ams Operation and Data Analysismentioning

confidence: 99%

Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications

et al. 2015

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Abstract. Elemental compositions of organic aerosol (OA) particles provide useful constraints on OA sources, chemical evolution, and effects. The Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is widely used to measure OA elemental composition. This study evaluates AMS measurements of atomic oxygento-carbon (O : C), hydrogen-to-carbon (H : C), and organic mass-to-organic carbon (OM : OC) ratios, and of carbon oxidation state (OS C ) for a vastly expanded laboratory data set of multifunctional oxidized OA standards. For the expanded standard data set, the method introduced by Aiken et al. (2008), which uses experimentally measured ion intensities at all ions to determine elemental ratios (referred to here as "Aiken-Explicit"), reproduces known O : C and H : C ratio values within 20 % (average absolute value of relative errors) and 12 %, respectively. The more commonly used method, which uses empirically estimated H 2 O + and CO + ion intensities to avoid gas phase air interferences at these ions (referred to here as "Aiken-Ambient"), reproduces O : C and H : C of multifunctional oxidized species within 28 and 14 % of known values. The values from the latter method are systematically biased low, however, with larger biases observed for alcohols and simple diacids. A detailed examination of the H 2 O + , CO + , and CO + 2 fragments in the high-resolution mass spectra of the standard compounds indicates that the Aiken-Ambient method underestimates the CO + and especially H 2 O + produced from many oxidized species. Combined AMS-vacuum ultraviolet (VUV) ionization measurements indicate that these ions are produced by dehydration and decarboxylation on the AMS vaporizer (usually operated at 600 • C). Thermal decomposition is observed to be efficient at vaporizer temperatures down to 200 • C. These results are used together to develop an "Improved-Ambient" elemental analysis method for AMS spectra measured in air. The Improved-Ambient method uses specific ion fragments as markers to correct for molecular functionality-dependent systematic biases and reproduces known O : C (H : C) ratios of individual oxidized standards within 28 % (13 %) of the known molecular values. The error in Improved-Ambient O : C (H : C) values is smaller for theoretical standard mixtures of the oxidized organic standards, which are more representative of the complex mix of species present in ambient Published by Copernicus Publications on behalf of the European Geosciences Union. M. R. Canagaratna et al.: Elemental ratio measurements of organic compoundsOA. For ambient OA, the Improved-Ambient method produces O : C (H : C) values that are 27 % (11 %) larger than previously published Aiken-Ambient values; a corresponding increase of 9 % is observed for OM : OC values. These results imply that ambient OA has a higher relative oxygen content than previously estimated. The OS C values calculated for ambient OA by the two methods agree well, however (average relative difference of 0.06 OS C units). This indicates that...

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“…The tunability and resolution [E/ΔE(fwhm) ≈ 250−400] of the photons' energy in the chemically interesting region from 7.4 to 30 eV allow for isomer specificity and near threshold ionization, i.e., reduced fragmentation. 20 The instrument's mass resolution of m/Δm ≈ 3500 enables a detailed analysis of a complex mixture of oxygenates and hydrocarbons. Further details of the JSR system and the MBMS instrument can be found elsewhere.…”

Section: Experimental Details and Data Evaluationmentioning

confidence: 99%

Quantification of the Keto-Hydroperoxide (HOOCH₂OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether

et al. 2016

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This work provides new temperature-dependent mole fractions of elusive intermediates relevant to the lowtemperature oxidation of dimethyl ether (DME). It extends the previous study of Moshammer et al. [J. Phys. Chem. A 2015, 119, 7361−7374] in which a combination of a jet-stirred reactor and molecular beam mass spectrometry with singlephoton ionization via tunable synchrotron-generated vacuumultraviolet radiation was used to identify (but not quantify) several highly oxygenated species. Here, temperature-dependent concentration profiles of 17 components were determined in the range of 450−1000 K and compared to up-to-date kinetic modeling results. Special emphasis is paid toward the validation and application of a theoretical method for predicting photoionization cross sections that are hard to obtain experimentally but essential to turn mass spectral data into mole fraction profiles. The presented approach enabled the quantification of the hydroperoxymethyl formate (HOOCH 2 OCH 2 O), which is a key intermediate in the low-temperature oxidation of DME. The quantification of this ketohydroperoxide together with the temperature-dependent concentration profiles of other intermediates including H 2 O 2 , HCOOH, CH 3 OCHO, and CH 3 OOH reveals new opportunities for the development of a next-generation DME combustion chemistry mechanism.

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Chemical dynamics, molecular energetics, and kinetics at the synchrotron

Cited by 75 publications

References 86 publications

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications

Quantification of the Keto-Hydroperoxide (HOOCH₂OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether

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Chemical dynamics, molecular energetics, and kinetics at the synchrotron

Cited by 75 publications

References 86 publications

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications

Quantification of the Keto-Hydroperoxide (HOOCH2OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether

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Quantification of the Keto-Hydroperoxide (HOOCH₂OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether