Methanetriol─Formation of an Impossible Molecule.

Orthocarboxylic acids─organic molecules carrying three hydroxyl groups at the same carbon atom─have been distinguished as vital reactive intermediates by the atmospheric science and physical (organic) chemistry communities as transients in the atmospheric aerosol cycle. Predicted short lifetimes and their tendency to dehydrate to a carboxylic acid, free orthocarboxylic acids, signify one of the most elusive classes of organic reactive intermediates, with even the simplest representative methanetriol (CH(OH)3)─historically known as orthoformic acid─not previously been detected experimentally. Here, we report the first synthesis of the previously elusive methanetriol molecule in low-temperature mixed methanol (CH3OH) and molecular oxygen (O2) ices subjected to energetic irradiation. Supported by electronic structure calculations, methanetriol was identified in the gas phase upon sublimation via isomer-selective photoionization reflectron time-of-flight mass spectrometry combined with isotopic substitution studies and the detection of photoionization fragments. The first synthesis and detection of methanetriol (CH(OH)3) reveals its gas-phase stability as supported by a significant barrier hindering unimolecular decomposition. These findings progress our fundamental understanding of the chemistry and chemical bonding of methanetriol, hydroxyperoxymethane (CH3OOOH), and hydroxyperoxymethanol (CH2(OH)OOH), which are all prototype molecules in the oxidation chemistry of the atmosphere.

Fulvenallenyl Radical (C7H5·)-Mediated Gas-Phase Synthesis of Bicyclic Aromatic C10H8 Isomers: Can Fulvenallenyl Efficiently React with Closed-Shell Hydrocarbons?

To understand the reactivity of resonantly stabilized radicals, often found in relevant concentrations in gaseous environments, it is important to determine their main reaction pathways. Here, it is investigated whether the fulvenallenyl radical (C7H5·) reacts preferentially with closed-shell molecules or radicals. Electronic structure calculations on the C10H9 potential energy surface accessed by the reactions of C7H5· with methylacetylene (CH3CCH) and allene (H2CCCH2) were combined with RRKM-ME calculations of temperature- and pressure-dependent rate constants using the automated EStokTP software suite and kinetic modeling to assess the reactivity of C7H5· with closed-shell unsaturated hydrocarbons. Experimentally, the reactions were attempted in a chemical microreactor heated to 998 ± 10 K by preparing fulvenallenyl radicals via pyrolysis of trichloromethylbenzene (C7H5Cl3) and seeding the radicals in methylacetylene or allene carrier gas, with product identification by means of photoionization mass spectrometry. The measured photoionization efficiency curve of m/z = 128 was assigned to a linear combination of the reference curves of two C10H8 isomers, azulene (minor) and naphthalene (major), presumably resulting from the C7H5· plus C3H4 reactions. However, the calculations demonstrated that these reactions are too slow, and kinetic modeling of processes in the reactor allowed us to conclude that the observation of naphthalene and azulene is due to the C7H5· plus C3H3· reaction, where propargyl is produced by direct hydrogen atom abstraction by chlorine (Cl) atoms from allene or methylacetylene and Cl stem from the pyrolysis of C7H5Cl3. Modeling results under the copyrolysis conditions of toluene and methylacetylene in high-temperature shock tube experiments confirmed the prevalence of the fulvenallenyl reaction with propargyl over its reactions with C3H4 even when the concentrations of allene and methylacetylene largely exceed that of propargyl. Overall, the reactions of fulvenallenyl with both allene and methylacetylene were found to be noncompetitive in the formation of naphthalene and azulene thus attesting the inefficiency of the fulvenallenyl radical reactions with the prototype closed-shell hydrocarbon species. In the meantime, the new reaction pathways revealed, including H-assisted isomerizations between C10H8 isomers and decomposition reactions of various C10H9 isomers, emerge as relevant and are recommended for inclusion in combustion kinetic models for naphthalene formation.

Study on the thermal oxidation of oleic, linoleic and linolenic acids by synchrotron radiation photoionization mass spectrometry.

RATIONALE: Cooking oil fumes contain numerous hazardous and carcinogenic chemicals, posing potential threats to human health. However, the sources of these species remain ambiguous, impeding health risk assessment, pollution control and mechanism research. METHODS: To address this issue, the thermal oxidation of three common unsaturated fatty acids (UFAs), namely oleic, linoleic and linolenic acids, present in vegetable oils was investigated. The volatile and semi-volatile products were comprehensively characterized by online synchrotron radiation photoionization mass spectrometry (SR-PIMS) with two modes, which were validated and complemented using offline gas chromatography (GC)/MS methods. Tunable SR-PIMS combined with photoionization efficiency curve simulation enabled the recognition of isomers/isobars in gaseous fumes. RESULTS: SR-PIMS revealed over 100 products, including aldehydes, alkenes, furans, aromatic hydrocarbons, etc., such as small molecules of formaldehyde, acetaldehyde, acrolein, ethylene and furan, which are not readily detected by conventional GC/MS; and some unreported fractions, e.g. ketene, 4-ethylcyclohexene and cycloundecene(E), were also observed. Furthermore, real-time monitoring of product emissions during the thermal oxidation of the three UFAs via SR-PIMS revealed that linolenic acid may be the major source of acrolein. CONCLUSION: SR-PIMS has been demonstrated as a powerful technique for online investigation of cooking oil fumes. This study achieved comprehensive characterization of volatile and semi-volatile products from the thermal oxidation of oleic, linoleic and linolenic acids, facilitating the traceability of species in cooking fumes and aiding in exploring the thermal reactions of different vegetable oils.

Probing combustion and catalysis intermediates by synchrotron vacuum ultraviolet photoionization molecular-beam mass spectrometry: recent progress and future opportunities.

Soft photoionization molecular-beam mass spectrometry (PI-MBMS) using synchrotron vacuum ultraviolet (SVUV) light has been significantly developed and applied in various fields in recent decades. Particularly, the tunability of SVUV light enables two-dimensional measurements, i.e. mass spectrum and photoionization efficiency spectrum measurements, affording isomer distinguishment in complex reaction processes. Many key intermediates have been successfully detected in combustion and catalysis reactions with the help of the state-of-the-art SVUV-PI-MBMS, promoting the understanding of the chemical mechanisms. Herein, we present a brief review of the instrumentation of beamline and PI-MBMS machines at the current synchrotron user facility Hefei Light Source II and exemplify the advantages of the SVUV-PI-MBMS method with recent applications in combustion and catalysis research, especially in probing key reaction intermediates. Future opportunities with the next generation synchrotron light source and bench-top light source have also been discussed.

Inception of Carbonaceous Nanostructures via Hydrogen-Abstraction Phenylacetylene-Addition Mechanism.

Sufficient experimental evidence has suggested that polycyclic aromatic hydrocarbons are the building blocks of carbonaceous nanostructures in combustion and circumstellar envelops of carbon-rich stars, but their fundamental formation mechanisms remain elusive. By exploring the reaction kinetics of phenylacetylene with 1-naphthyl/4-phenanthryl radicals, we provide compelling theoretical and experimental evidence for a novel and self-consistent hydrogen-abstraction phenylacetylene-addition (HAPaA) mechanism. HAPaA operates efficiently at both low and high temperatures, leading to the formation, expansion, and nucleation of peri-condensed aromatic hydrocarbons (PCAHs), which are otherwise difficult to synthesis via traditional hydrogen-abstraction acetylene/vinylacetylene-addition pathways. The HAPaA mechanism can be generalized to other α-alkynyl PCAHs and thus provides an alternative covalent bond bridge for PCAH combination via an acetylene linker. The proposed HAPaA mechanism may contribute toward a comprehensive understanding of soot formation, carbonaceous nanomaterials synthesis, and the origin and evolution of carbon in our galaxy.

Identification of Isobars and Isomers in Cigarette Sidestream Smoke in Real Time by Synchrotron Radiation Photoionization Mass Spectrometry and Multiple Linear Regression.

Direct analysis of chemical components in fresh cigarette smoke in real time is a challenging task. In this work, by using a novel continuous cigarette-pushing and smoke-introducing setup combined with synchrotron radiation photoionization mass spectrometry (SR-PIMS), the photoionization mass spectra of fresh gaseous cigarette sidestream smoke (SSS) from the combustion of solid tobacco could be recorded in real time, and the photoionization efficiency (PIE) curves of each mass peak could be obtained for the first time. Hence, lots of well-known chemical components and even isomers could be identified by their discriminated onsets or PIE curve simulation. Moreover, diimine, 2H-azirine, and sulfur monoxide, which have never been reported in cigarette smoke, were observed in cigarette SSS, and even two intermediates, ethenol and propen-2-ol, anticipated to exist were actually observed and distinguished. To increase the qualification accuracy, a new simulation method based on multiple linear regression (MLR) was developed and applied for the PIE curve simulation, where qualification mistakes caused by subjective judgements could be eliminated as far as possible.

Vacuum ultraviolet photochemistry of the conformers of the ethyl peroxy radical.

We study the conformers of the ethyl peroxy radical (C2H5O2), the simplest peroxy radical having more than one conformer, by combining synchrotron radiation vacuum ultraviolet (VUV) photoionization mass spectrometry with theoretical calculations. The ethyl peroxy radical is formed in a microwave discharge flow tube through the reaction of the ethyl radical (C2H5) with oxygen molecules, where C2H5 is generated via the hydrogen-abstraction reaction of ethane with fluorine atoms. Two kinds of C2H5+, originating from photoionization of C2H5 and from dissociative photoionization of C2H5O2, whose cation is not stable, have been identified and separated in photoionization mass spectra. The photoionization spectrum corresponding to C2H5O2 is obtained and assigned with Franck-Condon calculations. The present findings show that the gauche conformer (G-C2H5O2) of C2H5O2 has favorable Franck-Condon factors in the ionization transitions, whereas the contribution of the trans conformer (T-C2H5O2) to the photoionization spectrum is minor or negligible due to its large geometric changes in the photoionization process. Moreover, the reason for the instability of C2H5O2+ and its detailed dissociation mechanisms have been unraveled with the aid of the calculated potential energy curves.

Insights into the Decomposition and Oxidation Chemistry of p-Xylene in Laminar Premixed Flames.

This work reports an experimental and kinetic modeling investigation on laminar premixed flame of p-xylene at 0.04 atm and equivalence ratios of 0.75, 1.0, and 1.79. Intermediates such as the p-xylyl radical, p-xylylene, and styrene, as well as polycyclic aromatic hydrocarbons (PAHs), were detected by using synchrotron vacuum ultraviolet photoionization mass spectrometry. Based on our previous aromatic kinetic model, a detailed kinetic model of p-xylene combustion was developed, and the model was validated against the present flame structure data. Model analysis work was also performed in order to reveal the important reactions in p-xylene decomposition and oxidation. The H-abstraction reactions leading to the p-xylyl radical are found to control the consumption of p-xylene in all the three flames. In the rich flame, p-xylyl mainly suffers the H-elimination and isomerization reactions, which produce p-xylylene and the o-xylyl radical, respectively. The further decomposition reactions of the o-xylyl radical contribute to the production of styrene, which is another important C8 intermediate observed in the rich flame. In the stoichiometric and lean flames, p-xylyl mainly suffers the oxidation reactions by O, which give p-methylbenzaldehyde as major product. The growth pathways of PAHs in the rich flame were also investigated in this work. Indenyl, indene, naphthalene, and phenanthrene were observed as the abundantly produced bicyclic and tricyclic PAHs due to the existence of direct formation pathways from the decomposition of p-xylyl radical.

Atmospheric-Pressure Pyrolysis Study of Chlorobenzene Using Synchrotron Radiation Photoionization Mass Spectrometry.

The pyrolysis of chlorobenzene (C6H5Cl) at 760 Torr was studied in the temperature range of 873-1223 K. The pyrolysis products including intermediates and chlorinated aromatics were detected and quantified via synchrotron radiation photoionization mass spectrometry. Furthermore, the photoionization cross sections of chlorobenzene were experimentally measured. On the basis of the experimental results, the decomposition pathways of chlorobenzene were discussed as well as the generation and consumption pathways of the main products. Benzene is the main product of chlorobenzene pyrolysis. Chlorobiphenyl (C12H9Cl), dichlorobiphenyl (C12H8Cl2), and chlorotriphenylene (C18H11Cl) predominated in trace chlorinated aromatic products. Chlorobenzene decomposed initially to form two radicals [chlorophenyl (·C6H4Cl) and phenyl (·C6H5)] and the important intermediate o-benzyne (o-C6H4). The propagation processes of chlorinated aromatics, including polychlorinated naphthalenes and polychlorinated biphenyls, were mainly triggered by chlorobenzene, chlorophenyl, and benzene via the even-numbered-carbon growth mechanism. Besides, the small-molecule products such as acetylene (C2H2), 1,3,5-hexatriyne (C6H2), and diacetylene (C4H2) were formed via the bond cleavage of o-benzyne (o-C6H4).

Combined experimental and theoretical study on photoionization cross sections of benzonitrile and o/m/p-cyanotoluene.

Photoionization cross sections (PICSs) for the products of the reaction from CN with toluene, including benzonitrile and o/m/p-cyanotoluene, were obtained at photon energies ranging from ionization thresholds to 14 eV by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Theoretical calculations based on the frozen-core Hartree-Fock approximation and Franck-Condon simulations were carried out to cross-verify the measured PICS. The results show that the photoionization cross sections of benzonitrile and cyanotoluene isomers are similar. The generalized charge decomposition analysis was used to investigate the components of the highest occupied molecular orbital (HOMO) and HOMO-1. It was found that the HOMO and HOMO-1 of benzonitrile and cyanotoluene isomers are dominated by the features of the benzene ring, indicating that the substitution of CN and methyl has a minor influence on the PICS of the studied molecules. The reported PICS on benzonitrile and cyanotoluene isomers in the present work could contribute to the near-threshold PIMS experiments and determine the ionization and dissociation rates in interstellar space for these crucial species. The theoretical analysis on characteristics of molecular orbitals provides clues to estimating the PICS of similar substituted aromatic compounds.

Determination of absolute photoionization cross-sections of some aromatic hydrocarbons.

RATIONALE: Aromatic hydrocarbons play an important role in the formation and growth of polycyclic aromatic hydrocarbon (PAH) and soot particles. Measurements of their absolute photoionization cross-sections (PICSs), that benefit the quantitative investigation of mass spectrometry, are still lacking, however. METHODS: PICSs of some aromatic hydrocarbons were measured with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Nitric oxide and benzene were chosen as standard references for PICS calibration, since their photoionization cross-sections are well documented in the literature. Binary liquid mixtures of the investigated molecules and their specific solvents were used in the measurements. RESULTS: The investigated aromatics include naphthalene, phenanthrene, 1-methylnaphthalene, indene, 2-/3-/4-methylphenylacetylene, 2-methylindene, diphenylacetylene, 1-/2-ethynylnaphthalene and acenaphthylene. Photo-induced fragments from the molecules were also observed with increasing photon energy. CONCLUSIONS: Based on our measurements and literature data, PICSs of most aromatic molecules have very similar values beyond their ionization energies. However, molecules that contain the phenylacetylene structure have PICSs higher than other aromatics.

Radical Chemistry and Reaction Mechanisms of Propane Oxidative Dehydrogenation over Hexagonal Boron Nitride Catalysts.

Although hexagonal boron nitride (h-BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Now, the first direct experimental evidence of gas-phase methyl radicals (CH3 . ) in the ODHP reaction over boron-based catalysts is achieved by using online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV-PIMS), which uncovers the existence of gas-phase radical pathways. Combined with density functional theory (DFT) calculations, the results demonstrate that propene is mainly generated on the catalyst surface from the C-H activation of propane, while C2 and C1 products can be formed via both surface-mediated and gas-phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron-based catalysts.

Formation and Fate of Formaldehyde in Methanol-to-Hydrocarbon Reaction: In Situ Synchrotron Radiation Photoionization Mass Spectrometry Study.

HCHO has been confirmed as an active intermediate in the methanol-to-hydrocarbon (MTH) reaction, and is critical for interpreting the mechanisms of coke formation. Here, HCHO was detected and quantified during the MTH process over HSAPO-34 and HZSM-5 by in situ synchrotron radiation photoionization mass spectrometry. Compared with conventional methods, excellent time-resolved profiles were obtained to study the formation and fate of HCHO, and other products during the induction, steady-state reaction, and deactivation periods. Similar formation trends of HCHO and methane, and their close correlation in yields suggest that they are derived from disproportionation of methanol at acidic sites. In the presence of Y2 O3 , the amount of HCHO changes, affecting the hydrogen-transfer processes of olefins into aromatics and aromatics into cokes. The yield of HCHO affects the aromatic-based cycle and the formation of ethylene, indicating that ethylene is mainly formed from the aromatic-based cycle.

Imaging of Polar and Nonpolar Species Using Compact Desorption Electrospray Ionization/Postphotoionization Mass Spectrometry.

Desorption electrospray ionization (DESI) mass spectrometry imaging (MSI) can simultaneously record the 2D distribution of polar biomolecules in tissue slices at ambient conditions. However, sensitivity of DESI-MSI for nonpolar compounds is restricted by low ionization efficiency and strong ion suppression. In this study, a compact postphotoionization assembly combined with DESI (DESI/PI) was developed for imaging polar and nonpolar molecules in tissue sections by switching off/on a portable krypton lamp. Compared with DESI, higher signal intensities of nonpolar compounds could be detected with DESI/PI. To further increase the ionization efficiency and transport of charged ions of DESI/PI, the desorption solvent composition and gas flow in the ionization tube were optimized. In mouse brain tissue, more than 2 orders of magnitude higher signal intensities for certain neutral biomolecules like creatine, cholesterol, and GalCer lipids were obtained by DESI/PI in the positive ion mode, compared with that of DESI. In the negative ion mode, ion yields of DESI/PI for glutamine and some lipids (HexCer, PE, and PE-O) were also increased by several-fold. Moreover, nonpolar constituents in plant tissue, such as catechins in leaf shoots of tea, could also be visualized by DESI/PI. Our results indicate that DESI/PI can expand the application field of DESI to nonpolar molecules, which is important for comprehensive imaging of biomolecules in biological tissues with moderate spatial resolution at ambient conditions.

An experimental study of indene pyrolysis with synchrotron vacuum ultraviolet photoionization mass spectrometry.

Pyrolytic kinetics of indene was studied in a flow reactor at 30 and 760 Torr. Indene and its decomposition products, as well as polycyclic aromatic hydrocarbons (PAHs), were measured with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Five literature models were selected to reproduce the experimental data and analyze the reaction kinetics of indene. The experimental and predicted results illustrate that an indenyl radical is the dominant decomposition intermediate and also the main contributor to the further growth of aromatic rings in the pyrolysis of indene. The indene consumption process needs further precise characterization, especially the subsequent dissociation reactions of indanyl and indenyl radicals. A self-recombination reaction of the indenyl radical and the combination reactions between indenyl and other radicals are found to be necessary for the efficient formation of large PAHs. The absence of these pathways leads to the underprediction of experimental measurements. In contrast, literature models adopting indenyl global reactions for PAH formation generally overestimate the system reactivity. Proper radical combination pathways proposed in a future model should consider not only the PAH formation efficiency but also its impact on system reactivity.

Experimental and Theoretical Investigation of the Pyrolysis of Furfural.

The thermal decomposition of furfural is investigated in a flow tube reactor at 30 Torr by synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) at temperatures from 1023 to 1273 K. Over 20 kinds of pyrolysis products, including short-lived radicals, stable oxygen-containing compounds, and hydrocarbons, are identified from the scanning photoionization efficiency (PIE) spectra. Vinylketene (CH2═CH-CH═C═O), which has been shown to be an important primary product, is also directly observed. The possible steps of hydrogen atom addition and hydrogen atom abstraction in the thermal decomposition of furfural are studied by theoretical calculations at the CBS-QB3 level. In addition to unimolecular decomposition, hydrogen atom addition followed by ring opening can lead to the production of vinylketene.

Experimental and kinetic modeling investigation of rich premixed toluene flames doped with n-butanol.

n-Butanol is a promising renewable biofuel and has a lot of advantages as a gasoline additive compared with ethanol. Though the combustion of pure n-butanol has been extensively investigated, the chemical structures of large hydrocarbons doped with n-butanol, especially for aromatic fuels, are still insufficiently understood. In this work, rich premixed toluene/n-butanol/oxygen/argon flames were investigated at 30 Torr with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The blending ratio of n-butanol was varied from 0 to 50%, while the equivalence ratio was maintained at a quite rich value (1.75) for the purpose of studying the influence of n-butanol on the aromatic growth process. Flame species including radicals, reactive molecules, isomers and polycyclic aromatic hydrocarbons (PAHs) were identified and their mole fraction profiles were measured. A kinetic model of toluene/n-butanol combustion was developed from our recently reported toluene and n-butanol models. It is observed that the production of most toluene decomposition products and larger aromatics was suppressed as the blending ratio of n-butanol increases. Meanwhile, the addition of n-butanol generally enhanced the formation of most observed C2-C4 hydrocarbons and C1-C4 oxygenated species. The rate of production (ROP) analysis and experimental observations both indicate that the interaction between toluene and n-butanol in their decomposition processes mainly occurs at the formation of small intermediates, e.g. acetylene and methyl. In particular, the interaction between toluene and n-butanol in methyl formation influences the formation of large monocyclic aromatics such as ethylbenzene, styrene and phenylacetylene, making their maximum mole fractions decay slowly upon increasing the blending ratio of n-butanol compared with toluene and benzyl. The increase of the blending ratio of n-butanol reduces the formation of key PAH precursors such as benzyl, fulvenallenyl, benzene, phenyl and propargyl, which leads to a remarkable reduction in the formation of PAHs.

Fast and comprehensive characterization of chemical ingredients in traditional Chinese herbal medicines by extractive atmospheric pressure photoionization (EAPPI) mass spectrometry.

RATIONALE: The goal of this work is to employ extractive atmospheric pressure photoionization mass spectrometry (EAPPI-MS) to characterize the constituents in traditional Chinese herbal medicine (TCHM) directly without chromatographic separation. METHODS: Sample was placed in 4 mL of methanol/water (v/v, 3:1) in the nebulization cell, and then the ultrasonic nebulizer was switched on. The ultrasonic nebulization system allows the simultaneous sample extraction and introduction of extract aerosols. The extract aerosols were vaporized in a transfer tube. Mixed with a gaseous dopant, vaporized analytes were ionized through ambient photon-induced ion-molecule reactions, and were mass-analyzed by high-resolution time-of-flight mass spectrometry (TOF-MS). RESULTS: The major ingredients including alkaloids, flavonoids, amino acids, saccarides, ginsenosides, lignans and terpenoids were readily detected. Compared with electrospray ionization (ESI), EAPPI allowed the ionization of a wider range of compounds, which is desirable for the integral characterization of TCHMs containing numerous constituents. The significant discrepancies for both alkaloids and terpenoids in tripterygium glycoside tablets from two different manufacturers could be simultaneously reflected from EAPPI mass spectra. CONCLUSIONS: Our results demonstrate that EAPPI-MS can be regarded as a supplementary ambient method for the fast and comprehensive analysis of TCHMs, which is important for the quality control and safety assurance of these products.

The vacuum ultraviolet beamline/endstations at NSRL dedicated to combustion research.

An undulator-based vacuum ultraviolet (VUV) beamline (BL03U), intended for combustion chemistry studies, has been constructed at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. The beamline is connected to the newly upgraded Hefei Light Source (HLS II), and could deliver photons in the 5-21 eV range, with a photon flux of 10(13) photons s(-1) at 10 eV when the beam current is 300 mA. The monochromator of the beamline is equipped with two gratings (200 lines mm(-1) and 400 lines mm(-1)) and its resolving power is 3900 at 7.3 eV for the 200 lines mm(-1) grating and 4200 at 14.6 eV for the 400 lines mm(-1) grating. The beamline serves three endstations which are designed for respective studies of premixed flame, fuel pyrolysis in flow reactor, and oxidation in jet-stirred reactor. Each endstation contains a reactor chamber, an ionization chamber where the molecular beam intersects with the VUV light, and a home-made reflectron time-of-flight mass spectrometer. The performance of the beamline and endstations with some preliminary results is presented here. The ability to detect reactive intermediates (e.g. H, O, OH and hydroperoxides) is advantageous in combustion chemistry research.

Experimental and Modeling Investigation on the Pyrolysis of n-Decane Initiated by Nitropropane. Part I: 1-Nitropropane.

Initiators can accelerate the pyrolysis of hydrocarbon fuels, thereby reducing the required reaction temperature in the hypersonic vehicle heat exchanger/reactor. Nitro-alkanes are considered as efficient initiators due to their lower energy barrier of the C-N bond cleavage reaction. To research the mechanism of the initiation effect of nitro-alkanes on the decomposition of hydrocarbon fuel, synchrotron radiation vacuum ultraviolet photoionization-mass spectrometry (SVUV-PIMS) was employed to experimentally study the pyrolysis of n-C10H22, 1-C3H7NO2, and their binary mixtures in a flow tube under pressures of 30 and 760 Torr. The species identified and measured in the experiments included alkanes, alkenes, dialkenes, alkynes, nitrogen oxides, benzene, and free radicals, which revealed the mechanism of n-decane and 1-C3H7NO2 pyrolysis, as well as the interactions of the two fuels. Experiments show that the presence of 1-C3H7NO2 reduces the initial decomposition temperature of n-C10H22, and the increased pressures could achieve a stronger promoting effect on the conversion of n-C10H22. A detailed kinetic model containing 1769 reactions and 278 species was established and validated based on the mole fraction distributions of n-C10H22, major pyrolysis species, and important intermediates measured in pure fuel and initiated pyrolysis. The kinetic model can accurately predict the experimental data, and the mechanism of 1-C3H7NO2-initiated pyrolysis of n-C10H22 is analyzed with the model. The effect of 1-C3H7NO2 on the consumption of n-C10H22 and selectivity of cracked products is highlighted.