Absolute O<sub>2</sub>(aΔ) Concentration Measurement in Singlet Oxygen Generator by Using the Piston Source Method

Duo, Liping; Cui, Tieji; Wang, Zengqiang; Chen, Wenwu; Yang, Bojun; Sang, Fengting

doi:10.1021/jp0010379

Cited by 9 publications

(4 citation statements)

References 6 publications

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“…This pressure was chosen to reduce the residence time and, hence, the wall quenching of 1 O 2 inside the cold traps, gas tubing, and emission cell, so that maximum emission intensity could be detected. The emission detection system consists of a 5 nm bandwidth interference filter centered at 1270 nm (Andover, blocked to 1.55 μm), an optical chopper (SRS model SR540), a thermo-electrically cooled InGaAs photodetector (Newport model 71887 detector and 77055 TE-cooler controller), and a digital dual phase lock-in amplifier (SRS model SR830). ,, 1 O 2 emission from the emission cell was collected by a plano-convex BK7 lens (ThorLabs LA1805, f = 30 mm), passed through the optical chopper and the interference filter. The chopped emission was focused by another plano-convex BK7 lens (ThorLabs, LA1131, f = 50 mm, AR coated for 1050−1620 nm) into the InGaAs detector, and the signal was measured by the lock-in amplifier.…”

Section: Methodsmentioning

confidence: 99%

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): Reaction Dynamics and Collision Energy Effects

et al. 2011

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The reaction of protonated methionine with the lowest electronically excited state of molecular oxygen O(2)(a(1)Δ(g)) was studied in a guided ion beam apparatus, including the measurement of reaction cross sections over a center-of-mass collision energy (E(col)) range of 0.1-2.0 eV. A series of electronic structure and RRKM calculations were used to examine the properties of various complexes and transition states that might be important along the reaction coordinate. Only one product channel is observed, corresponding to generation of hydrogen peroxide via transfer of two hydrogen atoms (H2T) from protonated methionine to singlet oxygen. At low collision energies, the reaction approaches the collision limit and may be mediated by intermediate complexes. The reaction shows strong inhibition by collision energy, and becomes negligible at E(col) > 1.25 eV. A large set of quasi-classical direct dynamics trajectory simulations were calculated at the B3LYP/6-21G level of theory. Trajectories reproduced experimental results and provided insight into the mechanistic origin of the H2T reaction, how the reaction probability varies with impact parameter, and the suppressing effect of collision energy. Analysis of the trajectories shows that at E(col) = 1.0 eV the reaction is mediated by a precursor and/or hydroperoxide complex, and is sharply orientation-dependent. Only 20% of collisions have favorable reactant orientations at the collision point, and of those, less than half form precursor and hydroperoxide complexes which eventually lead to reaction. The narrow range of reactive collision orientations, together with physical quenching of (1)O(2) via intersystem crossing between singlet and triplet electronic states, may account for the low reaction efficiency observed at high E(col).

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Section: Methodsmentioning

confidence: 99%

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): Reaction Dynamics and Collision Energy Effects

et al. 2011

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“…The absolute concentrations of O 2 (a 1 ∆ g ), O 2 (b 1 Σ g ), and O( 3 P) were not determined using emission detection in the present experiment, but such a discharge typically produces 2.5-9% O 2 (a 1 ∆ g ), 10 -3 -10 -2 % O 2 (b 1 Σ g ), and 10 -4 % O( 3 P). 42,43 We calculated the deactivation of 1 O 2 (a 1 ∆ g ) due to self-quenching and collisional quenching by the wall and gaseous species 44,45 in the downstream tubing. The overall quenching rate is ∼0.05 s -1 , and the travel time of 1 O 2 (a 1 ∆ g ) downstream is <50 ms; thus the deactivation of 1 O 2 ( 1 ∆ g ) during its residence time in the system is <0.3%.…”

Section: Experimental Details a Instrument And Operating Conditionsmentioning

confidence: 99%

Reaction of Protonated Tyrosine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): An Experimental and Trajectory Study

Fang

Liu

2009

J. Phys. Chem. A

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Reaction of protonated tyrosine with the lowest electronically excited singlet state of molecular oxygen, (1)O(2) (a(1)Delta(g)), is reported over the center-of-mass collision energy (E(col)) range from 0.1 to 3.0 eV, using an electrospray-ionization, guided-ion-beam scattering instrument, in conjunction with ab initio electronic structure calculations and direct dynamics trajectory simulations. Only one product channel is observed, corresponding to generation of hydrogen peroxide via transfer of two hydrogen atoms from protonated tyrosine. Despite being exoergic, the reaction is in competition with physical quenching of (1)O(2) and is very inefficient. At low E(col), the reaction may be mediated by intermediate complexes and shows strong inhibition by collision energy. At high E(col), the reaction efficiency drops to approximately 1% and starts to have contribution from a direct mechanism. Quasi-classical trajectory simulations were performed to probe the mechanism at high collision energies. Analysis of trajectories shows that, at E(col) of 3.0 eV, a small fraction of hydrogen peroxide (25%) is produced via a direct, concerted mechanism where two hydrogen atoms are transferred simultaneously, but most hydrogen peroxide (75%) is formed by dissociation of hydroperoxide intermediates. According to ab initio calculations and trajectory simulations, collisions also lead to formation of various endoperoxides, and dissociation of endoperoxides may play a role in physical quenching of (1)O(2). The apparatus and experimental techniques are described in detail.

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“…Freshwater discharge to the Arctic Basin impacts ocean salinity as well as marine processes including sea ice formation and thermohaline circulation. Oceanographers typically define freshwater as the amount of zero salinity water contained in a volume compared to a reference salinity; Arctic Ocean freshwater budgets have been computed and updated since Aagaard and Carmack (1989).…”

Section: Introductionmentioning

confidence: 99%

Changing freshwater contributions to the Arctic

Stadnyk

Tefs

Broesky

et al. 2021

Elementa: Science of the Anthropocene

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The pan-Arctic domain is undergoing some of Earth’s most rapid and significant changes resulting from anthropogenic and climate-induced alteration of freshwater distribution. Changes in terrestrial freshwater discharge entering the Arctic Basin from pan-Arctic watersheds significantly impact oceanic circulation and sea ice dynamics. Historical streamflow records in high-latitude basins are often discontinuous (seasonal or with large temporal gaps) or sparse (poor spatial coverage), however, making trends from observed records difficult to quantify. Our objectives were to generate a more continuous 90-year record (1981–2070) of spatially distributed freshwater flux for the Arctic Basin (all Arctic draining rivers, including the Yukon), suitable for forcing ocean models, and to analyze the changing simulated trends in freshwater discharge across the domain. We established these data as valid during the historical period (1971–2015) and then used projected futures (preserving uncertainty by running a coupled climate-hydrologic ensemble) to analyze long-term (2021–2070) trends for major Arctic draining rivers. When compared to historic trends reported in the literature, we find that trends are projected to nearly double by 2070, with river discharge to the Arctic Basin increasing by 22% (on average) by 2070. We also find a significant trend toward earlier onset of spring freshet and a general flattening of the average annual hydrograph, with a trend toward decreasing seasonality of Arctic freshwater discharge with climate change and regulation combined. The coupled climate-hydrologic ensemble was then used to force an ocean circulation model to simulate freshwater content and thermohaline circulation. This research provides the marine research community with a daily time series of historic and projected freshwater discharge suitable for forcing sea ice and ocean models. Although important, this work is only a first step in mapping the impacts of climate change on the pan-Arctic region.

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Absolute O₂(aΔ) Concentration Measurement in Singlet Oxygen Generator by Using the Piston Source Method

Cited by 9 publications

References 6 publications

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): Reaction Dynamics and Collision Energy Effects

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): Reaction Dynamics and Collision Energy Effects

Reaction of Protonated Tyrosine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): An Experimental and Trajectory Study

Changing freshwater contributions to the Arctic

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Absolute O2(aΔ) Concentration Measurement in Singlet Oxygen Generator by Using the Piston Source Method

Cited by 9 publications

References 6 publications

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a1Δg): Reaction Dynamics and Collision Energy Effects

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a1Δg): Reaction Dynamics and Collision Energy Effects

Reaction of Protonated Tyrosine with Electronically Excited Singlet Molecular Oxygen (a1Δg): An Experimental and Trajectory Study

Changing freshwater contributions to the Arctic

Contact Info

Product

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About

Absolute O₂(aΔ) Concentration Measurement in Singlet Oxygen Generator by Using the Piston Source Method

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): Reaction Dynamics and Collision Energy Effects

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): Reaction Dynamics and Collision Energy Effects

Reaction of Protonated Tyrosine with Electronically Excited Singlet Molecular Oxygen (a¹Δ_g): An Experimental and Trajectory Study