The absolute photoionization cross section of the mercapto radical (SH) from threshold up to 15.0 eV

Hróðmarsson, Helgi Rafn; Garcia, Gustavo A.; Nahon, Laurent; Loison, Jean‐Christophe; Gans, Bérenger

doi:10.1039/c9cp05809e

Cited by 10 publications

(10 citation statements)

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“…The uncertainty in the mole fraction was evaluated to be within ±10% for the reactants, within ±20% for the intermediates with experimentally measured PICS, and estimated to a factor of 2 for the intermediates with calculated PICS. Note that in the rare occasions where experimental and simulated cross-sections are available, larger differences have been reported. , …”

Section: Experimental Facilities Theoretical Methods and Kinetic Modelmentioning

confidence: 99%

“…Note that in the rare occasions where experimental and simulated cross-sections are available, larger differences have been reported. 32,33 JSR Coupled to SVUV-PEPICO. Inside the SAPHIRS chamber 34 permanent end-station, located at one of the monochromatized branches of the DESIRS beamline at the SOLEIL synchrotron, a 100 μm sampling nozzle is connected to the JSR, which is operated at a pressure of 1.07 bar.…”

Section: Methods and Kinetic Modelmentioning

confidence: 99%

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Jet-Stirred Reactor Study of Low-Temperature Neopentane Oxidation: A Combined Theoretical, Chromatographic, Mass Spectrometric, and PEPICO Analysis

et al. 2021

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The oxidation of neopentane was studied in jet-stirred reactors at atmospheric pressure over a temperature range 500–850 K and ϕ = 0.5. The products were analyzed with chromatographic, mass spectrometric, and photoelectron spectroscopic setups complemented with theoretical calculations. This combination provides a comparison of photo-ionization mass spectrometry and gas chromatography for the quantification of mole fractions and highlights the relevant differences between them, while mass-tagged photoelectron spectroscopy sheds light onto the isomeric distribution. The new data and corresponding analyses are expected to provide valuable guidance for an extension of the kinetic model and the choice of experimental methods. The main first and second O2-addition products were observed in agreement with the literature (e.g., 3,3-dimethyloxetane, acetone, isobutene, and γ-ketohydroperoxide). The simulated mole fractions of the products using a literature kinetic model were compared to the experimental results. Even though the kinetic model has been validated previously, significant discrepancies between the measured and simulated mole fractions of 2-methylpropanal and methacrolein, two fuel-specific low-temperature oxidation products, were found. Furthermore, some experimentally observed species related to γ-ketohydroperoxide decomposition were not predicted indicating that the model is incomplete. The detection of 2-methylpropanal and formic acid highlighted the importance of the Korcek-type pathway.

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Section: Experimental Facilities Theoretical Methods and Kinetic Modelmentioning

confidence: 99%

Section: Methods and Kinetic Modelmentioning

confidence: 99%

Jet-Stirred Reactor Study of Low-Temperature Neopentane Oxidation: A Combined Theoretical, Chromatographic, Mass Spectrometric, and PEPICO Analysis

et al. 2021

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“…The integration is performed over the specific FUV radiation field at each position of the PDR. In particular, we took σ ion (SH) from Hrodmarsson et al (2019) and σ diss (H 2 S) from Zhou et al (2020), both determined in laboratory experiments. Figure 11 summarizes the relevant chemical network that leads to the formation of S-bearing hydrides and that we discuss in the following sections.…”

Section: Pdr Models Of S-bearing Hydridesmentioning

confidence: 99%

Bottlenecks to interstellar sulfur chemistry

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et al. 2021

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Hydride molecules lie at the base of interstellar chemistry, but the synthesis of sulfuretted hydrides is poorly understood and their abundances often crudely constrained. Motivated by new observations of the Orion Bar photodissociation region (PDR) – 1″ resolution ALMA images of SH+; IRAM 30 m detections of bright H232S, H234S, and H233S lines; H3S+ (upper limits); and SOFIA/GREAT observations of SH (upper limits) – we perform a systematic study of the chemistry of sulfur-bearing hydrides. We self-consistently determine their column densities using coupled excitation, radiative transfer as well as chemical formation and destruction models. We revise some of the key gas-phase reactions that lead to their chemical synthesis. This includes ab initio quantum calculations of the vibrational-state-dependent reactions SH+ + H2(v) ⇄ H2S+ + H and S + H2 (v) ⇄ SH + H. We find that reactions of UV-pumped H2(v ≥ 2) molecules with S+ ions explain the presence of SH+ in a high thermal-pressure gas component, Pth∕k ≈ 108 cm−3 K, close to the H2 dissociation front (at AV < 2 mag). These PDR layers are characterized by no or very little depletion of elemental sulfur from the gas. However, subsequent hydrogen abstraction reactions of SH+, H2S+, and S atoms with vibrationally excited H2, fail to form enough H2S+, H3S+, and SH to ultimately explain the observed H2S column density (~2.5 × 1014 cm−2, with an ortho-to-para ratio of 2.9 ± 0.3; consistent with the high-temperature statistical value). To overcome these bottlenecks, we build PDR models that include a simple network of grain surface reactions leading to the formation of solid H2S (s-H2S). The higher adsorption binding energies of S and SH suggested by recent studies imply that S atoms adsorb on grains (and form s-H2S) at warmer dust temperatures (Td < 50 K) and closer to the UV-illuminated edges of molecular clouds. We show that everywhere s-H2S mantles form(ed), gas-phase H2S emission lines will be detectable. Photodesorption and, to a lesser extent, chemical desorption, produce roughly the same H2S column density (a few 1014 cm−2) and abundance peak (a few 10−8) nearly independently of nH and G0. This agrees with the observed H2S column density in the Orion Bar as well as at the edges of dark clouds without invoking substantial depletion of elemental sulfur abundances.

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“…The experiments were carried out on the DESIRS beamline of the French synchrotron facility SOLEIL. The details of the experiment have been published previously, and they include the specificities of this setup and the procedure for determining the radical cross section, as well as detailed descriptions of energy calibrations and energy resolution. , Briefly, F atoms created from the dissociation of F 2 in a microwave discharge go on to react with helium-diluted NH 3 in a flow-tube reactor. Experimental conditions are controlled via mass spectrometry to optimize the single-H abstraction of NH 3 and to minimize all other side reactions (F addition, double-H abstraction, radical–radical reactions, etc.…”

Section: Methodsmentioning

confidence: 99%

Photoionization Cross Section of the NH₂ Free Radical in the 11.1–15.7 eV Energy Range

et al. 2021

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The NH 2 radical is a key component in many astrophysical environments, both in its neutral and cationic forms, being involved in the formation of complex N-bearing species. To gain insight into the photochemical processes into which it operates and to model accurately the ensuing chemical networks, the knowledge of its photoionization efficiency is required, but no quantitative determination has been carried out so far.Combining a flow-tube H-abstraction radical source, a double imaging photoelectronphotoion spectrometer and a vacuum-ultraviolet synchrotron excitation, the absolute photoionization cross section of the amino radical has been measured in the present 1 work for the first time at two photon energies: σ NH 2 ion (12.7 eV) = 7.8 ± 2.2 Mb and σ NH 2 ion (13.2 eV) = 7.8 ± 2.0 Mb. These values have been employed to scale the total ion yield previously recorded by Gibson et al. (JCP, 83, pp 4319-4328 (1985)). The resulting cross section curve spanning the 11.1-15.7 eV energy range will help in refining the current astrophysical models.

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The absolute photoionization cross section of the mercapto radical (SH) from threshold up to 15.0 eV

Abstract: We present the absolute photoionization cross-section of the mercapto radical, SH, recorded from its first ionization energy at 10.4 eV up to a photon energy of 15 eV.

Cited by 10 publications

References 73 publications

Jet-Stirred Reactor Study of Low-Temperature Neopentane Oxidation: A Combined Theoretical, Chromatographic, Mass Spectrometric, and PEPICO Analysis

Jet-Stirred Reactor Study of Low-Temperature Neopentane Oxidation: A Combined Theoretical, Chromatographic, Mass Spectrometric, and PEPICO Analysis

Bottlenecks to interstellar sulfur chemistry

Photoionization Cross Section of the NH₂ Free Radical in the 11.1–15.7 eV Energy Range

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The absolute photoionization cross section of the mercapto radical (SH) from threshold up to 15.0 eV

Abstract: We present the absolute photoionization cross-section of the mercapto radical, SH, recorded from its first ionization energy at 10.4 eV up to a photon energy of 15 eV.

Cited by 10 publications

References 73 publications

Jet-Stirred Reactor Study of Low-Temperature Neopentane Oxidation: A Combined Theoretical, Chromatographic, Mass Spectrometric, and PEPICO Analysis

Jet-Stirred Reactor Study of Low-Temperature Neopentane Oxidation: A Combined Theoretical, Chromatographic, Mass Spectrometric, and PEPICO Analysis

Bottlenecks to interstellar sulfur chemistry

Photoionization Cross Section of the NH2 Free Radical in the 11.1–15.7 eV Energy Range

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Photoionization Cross Section of the NH₂ Free Radical in the 11.1–15.7 eV Energy Range