Atomic Oxygen Radical Research Articles

Sheng‐Gui He

Angewandte Chemie International EditionVolume 57, Issue 43 p. 13964-13964 Author ProfileFree Access Sheng-Gui He First published: 06 June 2018 https://doi.org/10.1002/anie.201805999AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract “The natural talent I would like to be gifted with is a strong mind that never stops thinking. My motto is ‘failure is the mother of success’ …” Find out more about Sheng-Gui He in his Author Profile. Sheng-Gui He The author presented on this page has recently published his 10th article in Angewandte Chemie in the last 10 years: “Catalytic CO Oxidation by O2 Mediated by Noble-Metal-Free Cluster Anions Cu2VO3–5−”: L.-N. Wang, X.-N. Li, L.-X. Jiang, B. Yang, Q.-Y. Liu, H.-G. Xu, W.-J. Zheng, S.-G. He, Angew. Chem. Int. Ed. 2018, 57, 3349; Angew. Chem. 2018, 130, 3407. The work of S. G. He has been featured on the cover of Angewandte Chemie: “Formation of Gas-Phase Formate in Thermal Reactions of Carbon Dioxide with Diatomic Iron Hydride Anions”: L.-X. Jiang, C. Zhao, X.-N. Li, H. Chen, S.-G. He, Angew. Chem. Int. Ed. 2017, 56, 4187; Angew. Chem. 2017, 129, 4251. Date of birth: February 9, 1974 Position: Professor, Institute of Chemistry, Chinese Academy of Sciences E-mail: shengguihe@iccas.ac.cn Homepage: http://shengguihe.iccas.ac.cn/ ORCID: 0000-0002-9919-6909 Education: 1997 BS, University of Science and Technology of China (USTC) 2002 PhD with Prof. Qing-Shi Zhu, USTC 2002–2005 Postdoc with Prof. Dennis J. Clouthier, University of Kentucky 2005–2007 Postdoc with Prof. Elliot R. Bernstein, Colorado State University Awards: 2009 Young ScientistAward, Chinese Chemical Society; 2013 National Natural Science Fund for Distinguished Young Scholars Current research interests: Cluster chemistry; bond activation; ion–molecule reactions; mass spectrometry; photoelectron spectroscopy Hobbies: Hiking; reading The natural talent I would like to be gifted with is a strong mind that never stops thinking. My motto is “failure is the mother of success”. The greatest scientific advance of the last decades was artificial intelligence. When I was eighteen I wanted to be a scientist. I am waiting for the day when someone will discover alien life. The biggest challenge facing scientists is the opinion that scientists can solve all our problems. The most significant historic event of the past 100 years was the establishment of the People's Republic of China. If I could be anyone for a day, I would be an astronaut. My first experiment was to burn a piece of paper. My favorite way to spend a holiday is to go fishing. My favorite painter is Xu Beihong. My favorite composer is Pyotr Ilyich Tchaikovsky. My favorite book is Tao Te Ching. My 5 top papers: 1“Activation of Multiple C−H Bonds Promoted by Gold in AuNbO3+Clusters”: X.-N. Wu, X.-N. Li, X.-L. Ding, S.-G. He, Angew. Chem. Int. Ed. 2013, 52, 2444; Angew. Chem. 2013, 125, 2504. (Cationic gold stores electrons and drives bond activation.) 2“Reactivity of Atomic Oxygen Radical Anions Bound to Titania and Zirconia Nanoparticles in the Gas Phase: Low-Temperature Oxidation of Carbon Monoxide”: J.-B. Ma, B. Xu, J.-H. Meng, X.-N. Wu, X.-L. Ding, X.-N. Li, S.-G. He, J. Am. Chem. Soc. 2013, 135, 2991. (Reactive atomic oxygen radical anions were captured by isolated nanoparticles and characterized by mass spectrometry.) 3“CO Oxidation Catalyzed by Single Gold Atoms Supported on Aluminum Oxide Clusters”: Z.-Y. Li, Z. Yuan, X.-N. Li, Y.-X. Zhao, S.-G. He, J. Am. Chem. Soc. 2014, 136, 14307. (The mechanism of single-atom catalysis can be very well understood by studying doped atomic clusters.) 4“Thermal Methane Conversion to Syngas Mediated by Rh1-Doped Aluminum Oxide Cluster Cations RhAl3O4+”: Y.-K. Li, Z. Yuan, Y.-X. Zhao, C. Zhao, Q.-Y. Liu, H. Chen, S.-G. He, J. Am. Chem. Soc. 2016, 138, 12854. (A single atomic cluster can cleave all four C−H bonds of a methane molecule under thermal collision conditions.) 5“Formation of Gas-Phase Formate in Thermal Reactions of Carbon Dioxide with Diatomic Iron Hydride Anions”: L.-X. Jiang, C. Zhao, X.-N. Li, H. Chen, S.-G. He, Angew. Chem. Int. Ed. 2017, 56, 4187; Angew. Chem. 2017, 129, 4251. (The CO2 hydrogenation intermediate HCO2− was directly observed by mass spectrometry.) Volume57, Issue43October 22, 2018Pages 13964-13964 ReferencesRelatedInformation

Inactivation of microorganisms by radical droplets from combination of water discharge and electro-spraying

We report the generation of radical droplets activated by an underwater electrical discharge and the sterilization of bacteria cells by spraying the radical droplets to open air. The plasma formed by electrical discharge in a narrow dielectric capillary tube produces atomic oxygen, atomic hydrogen, and hydroxyl radicals from the dissociation of water vapor, which is achieved through Joule heating in the narrow capillary tube. The capillary discharge electrode is placed in a water flow line, and the plasma-activated water is sprayed as fine droplets through a nozzle at 0.08 L/min. In a bactericidal test, the droplets show a sterilization effect of more than 99.99% after an exposure time of 3 h. The proposed radical droplet generator may also be useful for the elimination of airborne microorganisms.

Chemical kinetics in an atmospheric pressure helium plasma containing humidity.

Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultra-violet high-resolution Fourier-transform absorption spectroscopy and ultra-violet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H2O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 × 1014 cm-3 for OH and 3 × 1013 cm-3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH+ by proton transfer to H2O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H2O+ by proton transfer to H2O and by electron impact dissociation of H2O. It is lost by reactions with other OH molecules to form either H2O + O or H2O2. Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications.

Plasma-Chemical Conversion of Hydrogen Sulfide in the Atmosphere of Methane with Addition of CO2 and O2

Plasma-chemical conversion of hydrogen sulfide in the atmosphere of methane with addition of CO2 and O2 in the nonequilibrium plasma of barrier discharge is studied. The degree of hydrogen sulfide removal reaches 97 vol%. The degree of methane transformation does not exceed 14 vol%. Gaseous reaction products contain hydrogen, carbon oxides, and C2–C4 hydrocarbons. The energy consumption for the removal of hydrogen sulfide ranges from 84 to 182 eV molecule−1. The process is accompanied by the formation of deposits on the surface of reactor electrodes. The composition of deposits is studied. Organic linear and cyclic polysulfides, as well as sulfones of various structures are identified in soluble components of deposits. Based on the experimental data and the results of theoretical estimates, a radical chain reaction mechanism is proposed. It is shown that the formation of polysulfide compounds with terminal alkyl and oxygen-containing groups is provided by the reactions between atomic oxygen, SH, and alkyl radical which were formed in the initial stages of processes in the non-equilibrium plasma of barrier discharge.

Enhanced electrical characteristics of a-Si thin films by hydrogen passivation with Nd3+:YAG laser treatment in underwater for photovoltaic applications

Post deposition underwater treatment with a nanosecond Nd3+:YAG laser is proposed and demonstrated for the passivation of electrical defects in 400–1000 nm-thick a-Si thin films needed for solar cells. The proposed pulsed laser beam-overlap technique also allows simultaneous annealing and texturing. Atomic hydrogen, oxygen, and hydroxyl radicals activated by the breakdown of water by laser heating passivate the dangling bonds in the crystal grains, improving the solar cell performance. The presence of hydrogen observed after water annealing using X-ray photo electron spectroscopy (XPS), Raman spectroscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) shows that the passivation improvement is caused by diffusion of atomic hydrogen. After underwater annealing, relative improvement in the life time of minority carriers was measured to be approximately 13% and the efficiency of n-aSi/p-cSi solar cells is found to be increased (~2 to 3%) when compared to that in air.

Influence of Oxygen Content on Argon/Oxygen Dielectric Barrier Discharge Plasma Treatment of Polyethylene Terephthalate Film

In this paper, the dielectric barrier discharge (DBD) is generated in argon/oxygen gas mixtures with various of oxygen content and is employed to treat Polyethylene terephthalate (PET) surface. The effects of oxygen content in the argon/oxygen feeding gas on the properties of DBD and surface properties of PET films are investigated by means of electrical measurements, optical diagnostics, and the surface characteristics analysis. It is shown that after all DBD plasma treatments, the water contact angles on the surface decrease and oxygen containing polar groups on the surface increase. The improvement of hydrophobicity on PET surface is found to be significantly influenced by the addition oxygen content. Adding a small content of oxygen to feeding gas can result in a more efficient treatment, while the discharge induces less effective treatments at relative large oxygen content. There exists an optimum oxygen content for the hydrophilicity improvement on the PET surface, and the lowest contact angle and the highest incorporation of oxygen-containing groups are obtained after argon/oxygen DBD treatment with 0.3% addition of oxygen, which is in agree with the optimum oxygen content for atomic oxygen generation in the discharge regime. The results can be explained by the influences of oxygen addition on the generation and quenching mechanisms of corresponding atomic oxygen radicals in the DBD plasma, which suggests that the efficiency of DBD plasma surface modification can be increased and controlled by a way of adding an appropriate ratio of oxygen into the carrier gas.

Does Each Atom Count in the Reactivity of Vanadia Nanoclusters?

Vanadium oxide cluster anions (V2O5)nVxOy- (n = 1-31; x = 0, 1; and x + y ≤ 5) with different oxygen deficiencies (Δ = 2y-1-5x = 0, ± 1, and ±2) have been prepared by laser ablation and reacted to abstract hydrogen atoms from alkane molecules (n-butane) in a fast flow reactor. When the cluster size n is less than 25, the Δ = 1 series [(V2O5)nO- clusters] that can contain atomic oxygen radical anions (O•-) generally have much higher reactivity than the other four cluster series (Δ = -2, -1, 0, and 2), indicating that each atom counts in the hydrogen-atom abstraction (HAA) reactivity. Unexpectedly, all of the five cluster series have similar HAA reactivity when the cluster size is greater than 25. The critical dimension of vanadia particles separating the cluster behavior (each atom counts) from the bulk behavior (each atom contributes a little part) is thus about 1.6 nm (∼V50O125). The strong electron-phonon coupling of the vanadia particles has been proposed to create the O•- radicals (V5+ = O2-+ heat → V4+-O•-) for the n > 25 clusters with Δ = -2, -1, 0, and 2. Such a mechanism is supported by a comparative study with the scandium system [(Sc2O3)nScxOy- (n = 1-29; x = 0, 1; and x + y ≤ 4)] for which the Δ = 1 series [(Sc2O3)nO- clusters] always have much higher HAA reactivity than the other cluster series.

Emission spectra of noble gases and their mixtures under ion beam excitation

AbstractThe luminescence spectra of noble gases and their binary mixtures were measured using heavy ion beam excitation from a DC-60 accelerator. Spectra were measured in the range of 200–975 nm; the gas spectra were dominated by lines ofp–sandd–patomic transitions; in neon and argon, lines from atomic oxygen, N2, N2+, and OH radical bands were also observed. The ultraviolet region of the spectra was represented by a “third continuum” of noble gases. In krypton, the band of the KrO excimer molecule with a maximum at 557 nm was also observed. The maxima of the heteronuclear ionic molecules bands were located at wavelengths of 329 and 506 nm (Ar–Xe), 491 nm (Kr–Xe), and 642 nm (Ar–Kr). The relative intensities of the 2p–1stransitions of the noble gases atoms were measured and are discussed.

Activation and Transformation of Ethane by Au2 VO3(+) Clusters with Closed-Shell Electronic Structures.

The study of chemical reactions between gold-containing heteronuclear oxide clusters and small molecules can provide molecular level mechanisms to understand the excellent activity of gold supported by metal oxides. While the promotion role of gold in alkane transformation was identified in the clusters with atomic oxygen radicals (O(-.)), the role of gold in the systems without O(-.) is not clear. By employing mass spectrometry and quantum chemistry calculations, the reactivity of Au2 VO3(+) clusters with closed-shell electronic structures toward ethane was explored. Both the dehydrogenation and ethene elimination channels were identified. It is gold rather than oxygen species initiating the C-H activation. The Au-Au dimer formed during the reactions plays important roles in ethane transformation. The reactivity comparison between Au2 VO3(+) and bare Au2(+) demonstrates that Au2 VO3(+) not only retains the property of bare Au2(+) that transforming ethane to dihydrogen, but also exhibits new functions in converting ethane to ethene, which reveals the importance of the composite system. This study provides a further understanding of the reactivity of metal oxide supported gold in alkane activation and transformation.

Surface reactions and structural evolution of organosilicate glass under Ar plasma bombardment

Ab initio molecular dynamics (AIMD) simulations with a variable time step setup were used to investigate collision reactions, collision cascades and subsequent structural changes of organosilicate glass (OSG) low-k dielectric surfaces under Ar plasma bombardment with kinetic energies up to 100eV. Reactions that result in carbon loss and glass network structure changes during plasma treatment were carefully examined, since carbon loss increases the dielectric constant of the low-k dielectrics and the susceptibility to water attack, thus adversely affecting the performance of these dielectric materials in microelectronic devices. Results from AIMD based collision cascade simulations have provided mechanistic understanding of collision reactions during plasma bombardment. It was found that Si–CH3 bond scission and CH3 abstraction reactions are the primary methods of carbon loss. Two distinct mechanisms were identified for CH3 removal from 100eV plasma bombardment, one due to direct momentum transfer from the high-energy incident Ar atom to a Si–O bond on the OSG surface, and the other due to generation of highly reactive atomic oxygen radicals during collision cascades. Atomic oxygen radicals generated during cascades were found to occur at a rate of 1–3 per 100eV Ar impact with radical kinetic energies ranging from 2.2 to 42.6eV, well above the minimum energy of 0.1eV for Si–CH3 bond breakage. Both reaction mechanisms were examined through atomic charge analysis and the results indicated that the Ar atom ionizes when it impacts the OSG surface, causing temporary charge transfer from the Ar atom to the Si–O bond and playing a role in CH3 removal. The cascading atomic oxygen radicals and the ionization of the Ar atom during the Si–CH3 bond scission and CH3 removal demonstrate the secondary effects of Ar bombardment which must be considered during plasma etching of low-k dielectrics.

Characterization and Effects of Ar/Air Microwave Plasma on Wound Healing

Using Ar/Air mixture microwave plasma, we investigated the effects of air and gas temperature on the generation of electrons, ozone (O3), and nitric oxide (NO) through experiments and chemical kinetics simulation. The global model (GM) chemical kinetics simulation was used to validate and complement experimental observations. As the air percentages in Ar plasma increase, electrons are mainly generated by reactive oxygen species (ROS), but electron densities decrease. This is why plasma jet length becomes shorter with the mixture of air to Ar plasma at the same power. The profile of O3 densities has a maximum point because these are affected by oxygen (O2) molecules and gas temperature. O3 densities increase because these are generated via recombination of atomic oxygen (O) and O2 radicals as the air percentages increase. As the gas temperature increases, O3 densities decrease and O3 radicals are mainly destroyed by ROS such as O2−, excited O2, and O, although air percentages increase. NO radicals increase continually with the addition of air mixture and increase in gas temperature. With respect to biomedical applications, in the case of Ar/Air plasma treatment, it takes just 2 d, which has reduced the wound area to 30% because of faster scab formation over the wound and mRNA activation. Abundant NO radicals with ROS in Ar/aAir plasma strongly enhance IL‐6 and TGF‐β1, which facilitate collagen remodeling and wound recovery effectively.

Gas-phase reaction of CeVO5(+) cluster ions with C2H4: the reactivity of cluster bonded peroxides.

Cerium-vanadium oxide cluster cations CeVO5(+) were generated by laser ablation, mass-selected using a quadrupole mass filter, thermalized through collisions with helium atoms, and then reacted with ethene molecules in a linear ion trap reactor. The cluster reactions have been characterized by time-of-flight mass spectrometry and density functional theory calculations. The CeVO5(+) cluster has a closed-shell electronic structure and contains a peroxide (O2(2-)) unit. The cluster bonded O2(2-) species is reactive enough to oxidize a C2H4 molecule to generate C2H4O2 that can be an acetic acid molecule. Atomic oxygen radicals (O(-)˙), superoxide radicals (O2(-)˙), and peroxides are the three common reactive oxygen species. The reactivity of cluster bonded O(-)˙ and O2(-)˙ radicals has been widely studied while the O2(2-) species were generally thought to be much less reactive or inert toward small molecules under thermal collision conditions. This work is among the first to report the reactivity of the peroxide unit on transition metal oxide clusters with hydrocarbon molecules, to the best of our knowledge.

Atomic Oxygen and Hydroxyl Radical Generation in Round Helium-Based Atmospheric-Pressure Plasma Jets by Various Electrode Arrangements and Its Application in Sterilizing Streptococcus mutans

The reactive chemical species generated in an atmospheric-pressure plasma jet (APPJ), such as hydroxyl radical and atomic oxygen, are generally regarded as the major sources for several biomedical applications. In this paper, we propose an APPJ with a 25-kHz high-voltage powered stainless steel tube fixed inside a quartz tube and an aluminum grounded electrode that is wrapped around the quartz tube. The results show that the radical intensities of atomic oxygen and hydroxyl radical, gas temperature, and power absorption increase with increasing distance of discharge gap distance under the same applied voltage. Increasing the width of grounded electrode increases gas temperature and causes higher power absorption but only slight change of radical generation. We have applied the APPJ with the conditions of highest radical generation (grounded electrode width $=$ discharge gap distance $= 15$ mm) for effectively sterilizing Streptococcus mutans within 15 s, which shows a highly potential application for root canal disinfection.

Low-lying electronic states of cyclopentadienone.

We report a combined experimental and theoretical study of the low-lying electronic states of cyclopentadienone (C5H4O). The cyclopentadienone anion (C5H4O(-)) was generated in the gas phase via reaction of atomic oxygen radical anions (O(-)) with cyclopentanone (C5H8O). Photoelectron imaging was used to gain access to the first three electronic states of C5H4O, including the X (1)A1 ground state and the (3)B2 and (3)A2 excited states. The first two state assignments are supported by the Franck-Condon simulations of the vibrational progressions observed in the X (1)A1 and (3)B2 bands in the photoelectron spectra. The adiabatic electron affinity of cyclopentadienone in the ground state is determined to be EA(X (1)A1) = 1.06 ± 0.01 eV, and the corresponding values for the first two excited states are EA((3)B2) = 2.56 ± 0.02 eV and EA((3)A2) = 3.45 ± 0.01 eV. These experimental determinations are in excellent agreement with the CCSD(T) theory predictions, lending further confidence to the above state assignments. On the basis of these results, the lowest singlet-triplet splitting (between the X (1)A1 and (3)B2 states) in cyclopentadienone is ΔES-T = 1.50 ± 0.02 eV.

Etching and Post‐Treatment Surface Stability of Track‐Etched Polycarbonate Membranes by Plasma Processing Using Various Related Oxidizing Plasma Systems

Oxidizing plasmas (O2, CO2, H2O (g), and formic acid (g)) were used to modify track‐etched polycarbonate (PC) membranes and explore the mechanisms and species responsible for etching. Etch rates were measured using scanning electron microscopy; modified surfaces were characterized with X‐ray photoelectron spectroscopy and water contact angle. These results were combined with optical emission spectroscopy to provide insight into etch mechanisms. Although oxide functionalities implanted were similar, H2O (g) and formic acid vapor plasmas yielded the lowest contact angles. The CO2, H2O (g), and formic acid (g) plasma‐modified surfaces were found to be similarly stable 1 month after treatment. Etch rate correlated directly to the relative gas‐phase density of atomic oxygen and hydroxyl radicals.

Ozone-Assisted Combustion—Part I: Literature Review and Kinetic Study Using Detailed n-Heptane Kinetic Mechanism

In this first paper, the authors undertake a review of the literature in the field of ozone-assisted combustion in order to summarize literature findings. The use of a detailed n-heptane combustion model including ozone kinetics helps analyze these earlier results and leads into experimentation within the authors' laboratory using a single-cylinder, direct-injection compression ignition engine, briefly discussed here and in more depth in a following paper. The literature and kinetic modeling outcomes indicate that the addition of ozone leads to a decrease in ignition delay, both in comparison to no added ozone and with a decreasing equivalence ratio. This ignition delay decrease as the mixture leans is counter to the traditional increase in ignition delay with decreasing equivalence ratio. Moreover, the inclusion of ozone results in slightly higher temperatures in the cylinder due to ozone decomposition, augmented production of nitrogen oxides, and reduction in particulate matter through radial atomic oxygen chemistry. Of additional importance, acetylene levels decrease but carbon monoxide emissions are found to both increase and decrease as a function of equivalence ratio. This work illustrates that, beyond a certain level of assistance (approximately 20 ppm for the compression ratio of the authors' engine), adding more ozone has a negligible influence on combustion and emissions. This occurs because the introduction of O3 into the intake causes a temperature-limited equilibrium set of reactions via the atomic oxygen radical produced.

Reactivity of Oxygen Radical Anions Bound to Scandia Nanoparticles in the Gas Phase: CH Bond Activation

The activation of C-H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O(-·)) is an important species in C-H activation. The mechanistic details of C-H activation by O(-·) radicals can be well understood by studying the reactions between O(-·) containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n-butane was studied by using a high-resolution time-of-flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n-butane by (Sc2O3)(N)O(-) (N=1-18) clusters was observed. The reactivity of (Sc2O3)(N)O(-) (N=1-18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13(-)) and 12 (Sc24O37(-)). Larger (Sc2O3)(N)O(-) clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)(N)O(-) (N=1-5) clusters, which were found to contain the O(-·) radicals as the active sites. The local charge environment around the O(-·) radicals was demonstrated to control the experimentally observed size-dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O(-·) containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C-H bond activation.

Influence of fast-heating processes and O atom production by a nanosecond spark discharge on the ignition of a lean [formula omitted]–air premixed flame

This paper presents 2D simulations of the ignition of a lean premixed H2–air flame by a nanosecond spark discharge between two-point electrodes at atmospheric pressure and at an initial temperature of 1000K. As a first step, it was assumed that thermal and chemical effects of the nanosecond spark discharge are the same in a lean H2–air mixture as in air. Comparing different models for the gas heating, we have shown that the fraction of the discharge energy going to gas heating for nanosecond spark discharges is in the range 20–30%, in agreement with literature values. The gas heating was found to start during the nanosecond voltage pulse as soon as the nanosecond spark channel is formed and the discharge energy is deposited non-uniformly in air with hot spots close to electrode tips. For the chemical effect, results show that in air, the atomic oxygen radical is mostly produced after the nanosecond voltage pulse due to the dissociative quenching of electronically excited N2. The maximum of the dissociation level of molecular oxygen is in the range 30%-60% in the plasma channel. Then, thermal and chemical effects of the nanosecond spark discharge on the ignition of a lean premixed H2–air flame have been studied separately. In both cases, a flame ignition was observed. Results show that thermal and chemical effects of the nanosecond spark on the ignition are of the same order with a slightly higher ignition efficiency for the chemical effect. Finally, we have taken into account simultaneously thermal and chemical effects and a synergistic activation has been observed.

Gas-phase organic reactions of the atomic oxygen radical cation

Reactivity of ground-state oxygen radical cation, O+(4S), has been studied with several organic compounds for the first time. Rate constants and product distributions have been measured for the ion-neutral reactions of O+ with acetaldehyde, acetic acid, acetone, dimethyl ether, methanol, and methyl formate at 300K in a flowing-afterglow-selected ion flow tube (FA-SIFT). The reactions observed proceed efficiently, occurring above 50% of the collision rate in each case. We observed highly exothermic charge transfer reactions which lead to dissociation in some cases. Other interesting trends in reactivity include attack on methyl groups, and for some reactions, O+ replaces the methyl radical.

Gas Temperature Effect on Reactive Species Generation from the Atmospheric Pressure Air Plasma

AbstractUsing surface type air atmospheric pressure plasma, we investigated the amount of ozone and other reactive species generation with variations of the surface temperature of an electrode through an optical emission spectrum and a tube type gas detector. Reduced version of global model (GM) was employed to complement these experimental observations. The results of the model matched well with the experimental data. The amount of ozone generated from the surface type air plasma device was dramatically reduced with increasing temperature. Atomic oxygen (O) and nitric oxide (NO) radicals, which are important agents for biomedical applications, proportionally increased with increasing temperature. We also elucidated the dominant reaction related to the generation or loss of these radicals based on temperature variation through our GM.