High-Resolution Double Velocity Map Imaging Photoelectron Photoion Coincidence Spectrometer for Gas-Phase Reaction Kinetics

Rösch, Daniel; Almeida, Raybel; Sztáray, Bálint; Osborn, David L.

doi:10.1021/acs.jpca.1c10293

Cited by 11 publications

(18 citation statements)

References 80 publications

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“…This conclusion is supported by our calculated rate coefficients for these processes and, for the H-assisted isomerization case, by the observation of an expected product, phenylacetylene. Additional measurements using more powerful isomer-resolved approaches, such as time-resolved photoelectron photoion coincidence spectroscopy, could reduce the uncertainty in experimental isomer quantification. Furthermore, experiments that directly probe H-assisted isomerization would also be valuable for more quantitative interpretation of radical–radical reactions in PAH formation.…”

Section: Discussionmentioning

confidence: 99%

Radical–Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction

et al. 2023

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The mechanism for hydrocarbon ring growth in sooting environments is still the subject of considerable debate. The reaction of phenyl radical (C6H5) with propargyl radical (H2CCCH) provides an important prototype for radical–radical ring-growth pathways. We studied this reaction experimentally over the temperature range of 300–1000 K and pressure range of 4–10 Torr using time-resolved multiplexed photoionization mass spectrometry. We detect both the C9H8 and C9H7 + H product channels and report experimental isomer-resolved product branching fractions for the C9H8 product. We compare these experiments to theoretical kinetics predictions from a recently published study augmented by new calculations. These ab initio transition state theory-based master equation calculations employ high-quality potential energy surfaces, conventional transition state theory for the tight transition states, and direct CASPT2-based variable reaction coordinate transition state theory (VRC-TST) for the barrierless channels. At 300 K only the direct adducts from radical–radical addition are observed, with good agreement between experimental and theoretical branching fractions, supporting the VRC-TST calculations of the barrierless entrance channel. As the temperature is increased to 1000 K we observe two additional isomers, including indene, a two-ring polycyclic aromatic hydrocarbon, and a small amount of bimolecular products C9H7 + H. Our calculated branching fractions for the phenyl + propargyl reaction predict significantly less indene than observed experimentally. We present further calculations and experimental evidence that the most likely cause of this discrepancy is the contribution of H atom reactions, both H + indenyl (C9H7) recombination to indene and H-assisted isomerization that converts less stable C9H8 isomers into indene. Especially at low pressures typical of laboratory investigations, H-atom-assisted isomerization needs to be considered. Regardless, the experimental observation of indene demonstrates that the title reaction leads, either directly or indirectly, to the formation of the second ring in polycyclic aromatic hydrocarbons.

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Section: Discussionmentioning

confidence: 99%

Radical–Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction

et al. 2023

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“…Figure S3 shows a linear dependence of S( 3 P 2 ) signal over a factor of 10 change in laser fluence, providing strong evidence that S( 3 P 2 ) is formed in a single-photon process. The O + SO → S + O 2 reaction is 6 kcal mol –1 endothermic and is therefore unlikely to explain the prompt production of S atoms we observe. However, this reaction is slightly exothermic for SO ( v = 3, 4) reactants, which each represent 6% of SO photoproducts in the photodissociation of SO 2 at 193 nm .…”

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confidence: 78%

“…We recently described a new photoelectron photoion coincidence (PEPICO) spectrometer and used 193 nm SO 2 photodissociation to demonstrate the instrument’s time-resolved capabilities . In addition to the expected O + SO product channel we found preliminary evidence of S( 3 P 2 ) production, but not its expected cofragment O 2 .…”

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confidence: 94%

“…Photodissociation to channel R1b should also produce a time-resolved O 2 signal, which we could not observe in our preliminary publication. 28 Observation of O 2 is especially challenging for two reasons: (1) there is always background O 2 signal from minor leaks of air into the vacuum chamber, and (2) the mass of 16 O 2 differs by only 0.018 amu from that of 32 S. To more efficiently detect O 2 we tuned the VUV photon energy to the first autoionizing resonance in the PI spectrum of O 2 at 12.344 eV. 35−37 The results are shown in Figure 3 Gaining additional insight into the photodissociation mechanism and the potential impacts that R1b may have on our understanding of Earth's Archean atmosphere and the Great Oxygenation Event requires measurement of the yields of R1a and R1b.…”

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confidence: 99%

“…The exiting gas forms a molecular beam that is ionized in a collisionless region of the vacuum chamber by tunable, quasi-continuous vacuum ultraviolet radiation. The resulting cations and electrons are detected in coincidence using velocity map imaging . Neutral species are identified from each cation/electron coincidence pair using multiple simultaneously collected observables: high-resolution ( m /Δ m = 4000) mass spectra, photoionization (PI) spectra, and mass-selected photoelectron spectra (ms-PES) and angular distributions (ms-PAD).…”

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SO₂ Photodissociation at 193 nm Directly Forms S(³P) + O₂(³Σ_g^–): Implications for the Archean Atmosphere on Earth

Rösch

Guo

et al. 2023

J. Phys. Chem. Lett.

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It is well-documented that photodissociation of SO2 at λ = 193 nm produces O(3P j ) + SO X(3Σ–). We provide experimental evidence of a new product channel from one-photon absorption producing S(3P j ) + O2 X(3Σg –) in 2–4% yield. We probe the reactant and all products with time-resolved photoelectron photoion coincidence spectroscopy. High-level ab initio calculations suggest that the new product channel can only occur on the ground-state potential energy surface through internal conversion from the excited state, followed by isomerization to a transient SOO intermediate. Classical trajectories on the ground-state potential energy surface with random initial conditions qualitatively reproduce the experimental yields. This unexpected photodissociation pathway may help reconcile discrepancies in sulfur mass-independent fractionation mechanisms in Earth’s geologic history, which shape our understanding of the Archean atmosphere and the Great Oxygenation Event in Earth’s evolution.

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Photoelectron Photoion Coincidence Spectroscopy of Biradicals

Fischer

Hemberger

2023

ChemPhysChem

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The electronic structure of biradicals is characterized by the presence of two unpaired electrons in degenerate or near‐degenerate molecular orbitals. In particular, some of the most relevant species are highly reactive, difficult to generate cleanly and can only be studied in the gas phase or in matrices. Unveiling their electronic structure is, however, of paramount interest to understand their chemistry. Photoelectron photoion coincidence (PEPICO) spectroscopy is an excellent approach to explore the electronic states of biradicals, because it enables a direct correlation between the detected ions and electrons. This permits to extract unique vibrationally resolved photoion mass‐selected threshold photoelectron spectra (ms‐TPES) to obtain insight in the electronic structure of both the neutral and the cation. In this review we highlight most recent advances on the spectroscopy of biradicals and biradicaloids, utilizing PEPICO spectroscopy and vacuum ultraviolet (VUV) synchrotron radiation.

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High-Resolution Double Velocity Map Imaging Photoelectron Photoion Coincidence Spectrometer for Gas-Phase Reaction Kinetics

Cited by 11 publications

References 80 publications

Radical–Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction

Radical–Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction

SO₂ Photodissociation at 193 nm Directly Forms S(³P) + O₂(³Σ_g^–): Implications for the Archean Atmosphere on Earth

Photoelectron Photoion Coincidence Spectroscopy of Biradicals

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High-Resolution Double Velocity Map Imaging Photoelectron Photoion Coincidence Spectrometer for Gas-Phase Reaction Kinetics

Cited by 11 publications

References 80 publications

Radical–Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction

Radical–Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction

SO2 Photodissociation at 193 nm Directly Forms S(3P) + O2(3Σg–): Implications for the Archean Atmosphere on Earth

Photoelectron Photoion Coincidence Spectroscopy of Biradicals

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SO₂ Photodissociation at 193 nm Directly Forms S(³P) + O₂(³Σ_g^–): Implications for the Archean Atmosphere on Earth