Plasma Chemistry Research Articles

A Quantum Chemical Investigation into the Molecular Mechanism of the Atmospheric Reactions of Chemi-Ions with Nitrogen and Nitrogen Oxides.

Nitrogen oxides and chemi-ions are atmospheric pollutants with considerable aeronomic interest. These toxicants can react with each other, producing various ionic species and highly reactive by-products that play a crucial role in aerosol clustering and mediate several important atmospheric reactions. Understanding the chemical reactivity of these pollutants can provide essential information for controlling their excess emission into the atmosphere. Computational modeling and electronic structure studies help in predicting the structure, reactivity, and thermodynamics of transient atmospheric chemical species and can guide experimental research by providing vital mechanistic insights and data. In the present study, a computational investigation into the mechanisms of the binary associative reactions between negative ions: O2− and O3− with NO, NO2, and N2 was conducted using the Coupled-Cluster Singles and Doubles (CCSD) theory. Five model reactions between N2/NOx with On− (n = 2, 3) were considered in this work. Our calculations revealed that reactions (2) and (5) are two sequential processes involving intermediates, and all others occur in a concerted manner by direct transitions from the reactants to the products, with no isolable intermediates proceeding via single non-planar transition states. Our study revealed that the higher activation barrier required for the formation of NO3− (2) as compared to NO2− (1) could be the reason for the excess formation of NO2− ions over NO3− ions in the atmosphere. Further, all the investigated reactions except (5) are found to be feasible at room temperature. The energy required to break N-N bonds in the N2 molecule justifies the high barrier for (5). The results obtained from the study are in close agreement with the available experimental data. Moreover, the data from the study can be utilized for the evaluation of experiments and model predictions pertaining to NOx oxidation and molecular modeling of the gas-phase chemistry of pollutants/nucleation precursors formed in the Earth’s atmosphere and aircraft engines.

The N(2D) + CH2CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan.

The reaction of electronically excited nitrogen atoms, N(2D), with vinyl cyanide, CH2CHCN, has been investigated under single-collision conditions by the crossed molecular beam (CMB) scattering method with mass spectrometric detection and time-of-flight (TOF) analysis at the collision energy, Ec, of 31.4 kJ/mol. Synergistic electronic structure calculations of the doublet potential energy surface (PES) have been performed to assist in the interpretation of the experimental results and characterize the overall reaction micromechanism. Statistical (Rice–Ramsperger–Kassel–Marcus, RRKM) calculations of product branching fractions (BFs) on the theoretical PES have been carried out at different values of temperature, including the one corresponding to the temperature (175 K) of Titan’s stratosphere and at a total energy corresponding to the Ec of the CMB experiment. According to our theoretical calculations, the reaction is found to proceed via barrierless addition of N(2D) to the carbon–carbon double bond of CH2=CH–CN, followed by the formation of cyclic and linear intermediates that can undergo H, CN, and HCN elimination. In competition, the N(2D) addition to the CN group is also possible via a submerged barrier, leading ultimately to N2 + C3H3 formation, the most exothermic of all possible channels. Product angular and TOF distributions have been recorded for the H-displacement channels leading to the formation of a variety of possible C3H2N2 isomeric products. Experimentally, no evidence of CN, HCN, and N2 forming channels was observed. These findings were corroborated by the theory, which predicts a variety of competing product channels, following N(2D) addition to the double bond, with the main ones, at Ec = 31.4 kJ/mol, being six isomeric H forming channels: c-CH(N)CHCN + H (BF = 35.0%), c-CHNCHCN + H (BF = 28.1%), CH2NCCN + H (BF = 26.3%), c-CH2(N)CCN(cyano-azirine) + H (BF = 7.4%), trans-HNCCHCN + H (BF = 1.6%), and cis-HNCCHCN + H (BF = 1.3%), while C–C bond breaking channels leading to c-CH2(N)CH(2H-azirine) + CN and c-CH2(N)C + HCN are predicted to be negligible (0.02% and 0.2%, respectively). The highly exothermic N2 + CH2CCH (propargyl) channel is also predicted to be negligible because of the very high isomerization barrier from the initial addition intermediate to the precursor intermediate able to lead to products. The predicted product BFs are found to have, in general, a very weak energy dependence. The above cyclic and linear products containing an additional C–N bond could be potential precursors of more complex, N-rich organic molecules that contribute to the formation of the aerosols on Titan’s upper atmosphere. Overall, the results are expected to have a significant impact on the gas-phase chemistry of Titan’s atmosphere and should be properly included in the photochemical models.

Effects of prenol and isoprenol addition on soot and PAH formation in ethylene/methane counterflow diffusion flames

Prenol has attracted much attention due to its high heating value and novel octane hyperboosting phenomenon; while its soot formation behavior is not studied yet. In this study, experimental and numerical analysis of the effects of prenol and isoprenol addition on polycyclic aromatic hydrocarbon (PAH) and soot formation in non-premixed ethylene/methane flames is performed. Distribution of soot volume fraction and PAHs in the flames is measured via laser induced incandescence and laser induced fluorescence, respectively. The results show that both prenol and isoprenol addition enhances soot and PAH formation in ethylene/methane flames, and the prenol shows a stronger enhancing effect. Modeling of the sooting behavior is performed with a constructed gas-phase chemistry and a sectional method. The numerical results well capture the experimental observations and reveal that the increased concentrations of C2H2, C3H3 or C4H6 after prenol or isoprenol blending chemically promote benzene ring formation, subsequent PAH growth and soot formation processes. ROP (rate of production) analysis is performed to investigate the effect of prenol and isoprenol addition on rate-limiting ring formation process. In methane and ethylene flame, prenol or isoprenol blending promotes benzene formation in different ways, due to the discrepancies on the radical pool in two flames. Moreover, prenol also shows stronger effect on both of soot inception rate and surface growth rate than isoprenol, which is due to more PAHs and C2H2 formed in the prenol-doping flames. Reaction pathway analysis shows that decomposition of prenol generates C2H2 and C3H3 while isoprenol mainly generate C3H3 and almost no C2H2, the distinctive decomposition pathways of prenol results in its higher formation propensity of PAHs and soot.

The 2021 release of the Quantemol database (QDB) of plasma chemistries and reactions

The Quantemol database (QDB) provides cross sections and rates of processes important for plasma models; heavy particle collisions (chemical reactions) and electron collision processes are considered. The current version of QDB has data on 28 917 processes between 2485 distinct species plus data for surface processes. These data are available via a web interface or can be delivered directly to plasma models using an application program interface; data are available in formats suitable for direct input into a variety of popular plasma modeling codes including HPEM, COMSOL, ChemKIN, CFD-ACE+, and VisGlow. QDB provides ready assembled plasma chemistries plus the ability to build bespoke chemistries. The database also provides a Boltzmann solver for electron dynamics and a zero-dimensional model. Thesedevelopments, use cases involving O2, Ar/NF3, Ar/NF3/O2, and He/H2O/O2 chemistries, and plans for the future are presented.

Measurements from inside a Thunderstorm Driven by Wildfire: The 2019 FIREX-AQ Field Experiment

Abstract The 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field experiment obtained a diverse set of in situ and remotely sensed measurements before and during a pyrocumulonimbus (pyroCb) event over the Williams Flats fire in Washington State. This unique dataset confirms that pyroCb activity is an efficient vertical smoke transport pathway into the upper troposphere and lower stratosphere (UTLS). The magnitude of smoke plumes observed in the UTLS has increased significantly in recent years, following unprecedented wildfire and pyroCb activity observed worldwide. The FIREX-AQ pyroCb dataset is therefore extremely relevant to a broad community, providing the first measurements of fresh smoke exhaust in the upper troposphere, including from within active pyroCb cloud tops. High-resolution remote sensing reveals that three plume cores linked to localized fire fronts, burning primarily in dense forest fuels, contributed to four total pyroCb “pulses.” Rapid changes in fire geometry and spatial extent dramatically influenced the magnitude, behavior, and duration of pyroCb activity. Cloud probe measurements and weather radar identify the presence of large ice particles within the pyroCb and hydrometers below cloud base, indicating precipitation development. The resulting feedbacks suggest that vertical smoke transport efficiency was reduced slightly when compared with intense pyroCb events reaching the lower stratosphere. Physical and optical aerosol property measurements in pyroCb exhaust are compared with previous assumptions. A large suite of aerosol and gas-phase chemistry measurements sets a foundation for future studies aimed at understanding the composition of smoke plumes lifted by pyroconvection into the UTLS and their role in the climate system.

NanoParticle Flow Reactor (NanoPFR): a tested model for simulating carbon nanoparticle formation in flow reactors

Abstract Flow reactors are widely used to study the formation of various nanoparticles, such as carbon black, soot, nickel, titania, and silica. Such reactors provide well-controlled conditions, making them a favored laboratory tool to investigate the details of particle formation. Here we present NanoParticle Flow Reactor (NanoPFR), a detailed model to simulate nanoparticle synthesis in flow reactors. The model predicts the agglomerate fractal-like morphology and size distribution with a 2-variable sectional population balance model coupled with gas-phase chemistry. The particle formation processes employed in the code are tested using detailed discrete element modeling simulations and then used to predict carbon black formation from ethylene pyrolysis experiments from the literature. The code is a robust flow reactor predictive tool with a strong foundation that can serve as a basis for further development, including the simulation of other nanoparticles formation.

Refined Appearance Potential Mass Spectrometry for High Precision Radical Density Quantification in Plasma.

As the analysis of complicated reaction chemistry in bulk plasma has become more important, especially in plasma processing, quantifying radical density is now in focus. For this work, appearance potential mass spectrometry (APMS) is widely used; however, the original APMS can produce large errors depending on the fitting process, as the fitting range is not exactly defined. In this research, to reduce errors resulting from the fitting process of the original method, a new APMS approach that eliminates the fitting process is suggested. Comparing the neutral densities in He plasma between the conventional method and the new method, along with the real neutral density obtained using the ideal gas equation, confirmed that the proposed quantification approach can provide more accurate results. This research will contribute to improving the precision of plasma diagnosis and help elucidate the plasma etching process.

Consistent thermodynamics for plasma-assisted combustion

Excited-state species are a vital component of plasma chemistry modeling. Many previous works have studied the reactions of excited-state species. In almost all of these studies, the thermodynamic properties of the excited states are obtained via a modification of the formation enthalpy. It is often assumed that the error introduced by this procedure can be neglected. However, this is not true when vibrational states are included in the chemical mechanism. Specifically, we find that the error in adiabatic flame temperature can be as high as 100 K, and the error in NO concentration is as large as 50%. In this work, we will demonstrate how to consistently compute the thermodynamic data for these species. Key in computing thermodynamic data for excited-state species is the realization that an excited state is a subset of a full molecule description. The main challenge then becomes the consistently distributing the internal states over individual species.

Deep learning-based gas-phase chemical kinetics kernel emulator: Application in a global air quality simulation case

The global atmospheric chemical transport model has become a key technology for air quality forecast and management. However, precise and rapid air quality simulations and forecast are frequently limited by the model’s computational performance. The gas-phase chemistry module is the most time-consuming module in air quality models because its traditional solution method is dynamically stiff. To reduce the solving time of the gas phase chemical module, we built an emulator based on a deep residual neural network emulator (NN) for Carbon Bond Mechanism Z (CBM-Z) mechanism implemented in Global Nested Air Quality Prediction Modeling System. A global high resolution cross-life multi-species dataset was built and trained to evaluate multi-species concentration changes at a single time step of CBM-Z. The results showed that the emulator could accelerate to approximately 300–750 times while maintaining an accuracy similar to that of CBM-Z module (the average correlation coefficient squared was 0.97) at the global scale. This deep learning-based emulator could adequately represent the stiff kinetics of CBM-Z, which involves 47 species and 132 reactions. The emulated ozone (O3), nitrogen oxides (NOx), and hydroxyl radical (OH) were consistent with those of the original CBM-Z module in different global regions, heights, and time. Our results suggest that data-driven emulations have great potential in the construction of hybrid models with process-based air quality models, particularly at larger scales.

Nanosecond pulsed plasma assisted combustion of ammonia-air mixtures: Effects on ignition delays and [formula omitted] emission

Computational investigation of plasma assisted combustion of ammonia-air mixtures in constant volume and constant pressure reactors are conducted, to determine the impact of operating conditions on ignition delays and NOx emissions. Due to the lack of a chemical kinetic mechanism for plasma discharge of ammonia (NH3)/air mixtures, a mechanism has been assembled in this work using well-validated plasma reactions of NH3 with O2 and N2, alongside plasma kinetics of air from the literature. The impact of the reduced electric field (E/N), equivalence ratio, pressure, pulse frequency and the energy density on the ignition delays and NO/NO2 emission is discussed. At lower E/N, vibrational-to-translational (VT) relaxation of the vibrational states of NH3 and N2 is observed to play a dominant role in the gas heating process on account of the higher vibrational energy contribution. The ignition event is observed to be faster for fuel-lean mixture (ϕ = 0.5) compared to stoichiometric and fuel-rich (ϕ = 1.2) conditions owing to the lower consumption of OH radicals through the reactivity-inhibiting reaction NH3+OH→NH2+H2O between plasma pulses for leaner mixtures. Nevertheless, the fuel-lean mixture is observed to exhibit higher production of NOx than stoichiometric and fuel-rich mixtures, resulting from plasma chemistry involving oxygen radical and electronic excited states of N2. At the higher pressure of 3 atm, the pressure dependent recombination reaction H+O2+M→HO2+M is found to delay the ignition by limiting the reactive radicals compared to the corresponding 1 atm case. Higher rates of collisional quenching at higher pressures during the inter-pulse gaps resulted in lesser amount of electronically excited states of N2 and O2, which resulted in lower production of air-bound NOx during the pulses. Pulse frequency and energy density per pulse are seen to exhibit an inversely proportional effect on the ignition delay times. Most importantly, a faster ignition and lower production of NOx is observed in the case of plasma discharges compared to thermal energy deposition, owing to the enhanced production of OH radicals and the reforming of NH3 to produce N2 with plasma, respectively. Interesting roles of fuel-radicals such as NH2 and NH in both producing and reducing NO at different instants have also been discussed.

Plasmas for in situ resource utilization on Mars: Fuels, life support, and agriculture

This work discusses the potential of combining non-thermal plasmas and conducting membranes for in situ resource utilization (ISRU) on Mars. By converting different molecules directly from the Martian atmosphere, plasmas can create the necessary feed-stock and base chemicals for processing fuels, breathing oxygen, building materials, and fertilizers. Different plasma sources operate according to different principles and are associated with distinct dominant physicochemical mechanisms. This diversity allows exploring different energy transfer pathways leading to CO2 dissociation, including direct electron-impact processes, plasma chemistry mediated by vibrationally and electronically excited states, and thermally driven dissociation. The coupling of plasmas with membranes is still a technology under development, but a synergistic effect between plasma decomposition and oxygen permeation across conducting membranes is anticipated. The emerging technology is versatile, scalable, and has the potential to deliver high rates of production of molecules per kilogram of instrumentation sent to space. Therefore, it will likely play a very relevant role in future ISRU strategies.

The SINQ gas-jet facility as a source for radionuclides from neutron-induced fission of 235U

The Swiss Spallation Neutron Source SINQ of the Paul Scherrer Institute provides neutrons via proton-induced spallation reactions in a lead target. Produced neutrons are thermalized and impinge on 235U-targets, enclosed in a three-part chamber assembly, which is located in the inner wall of the SINQ shielding. The thermal-neutron-induced fission products can be readily transported from this chamber assembly to a radiochemical laboratory using the gas-jet technique either with a pure carrier gas or with an aerosol-particle-loaded carrier gas. In the past, mainly radioisotopes of the elements Se, Br, Rb, and Kr were retrieved and used for gas-phase chemistry experiments. Here, we present first experiments after the commissioning of the SINQ gas-jet facility as a source of recoverable, non-volatile and volatile, carrier-free fission products for general radiochemical studies and other applications.

Low-Temperature Plasma Diagnostics to Investigate the Process Window Shift in Plasma Etching of SiO2.

As low-temperature plasma plays an important role in semiconductor manufacturing, plasma diagnostics have been widely employed to understand changes in plasma according to external control parameters, which has led to the achievement of appropriate plasma conditions normally termed the process window. During plasma etching, shifts in the plasma conditions both within and outside the process window can be observed; in this work, we utilized various plasma diagnostic tools to investigate the causes of these shifts. Cutoff and emissive probes were used to measure the electron density and plasma potential as indicators of the ion density and energy, respectively, that represent the ion energy flux. Quadrupole mass spectrometry was also used to show real-time changes in plasma chemistry during the etching process, which were in good agreement with the etching trend monitored via in situ ellipsometry. The results show that an increase in the ion energy flux and a decrease in the fluorocarbon radical flux alongside an increase in the input power result in the breaking of the process window, findings that are supported by the reported SiO2 etch model. By extending the SiO2 etch model with rigorous diagnostic measurements (or numerous diagnostic methods), more intricate plasma processing conditions can be characterized, which will be beneficial in applications and industries where different input powers and gas flows can make notable differences to the results.

Atomic Layer Deposition of Large-Area Polycrystalline Transition Metal Dichalcogenides from 100 °C through Control of Plasma Chemistry.

Two-dimensional transition metal dichalcogenides, such as MoS2, are intensely studied for applications in electronics. However, the difficulty of depositing large-area films of sufficient quality under application-relevant conditions remains a major challenge. Herein, we demonstrate deposition of polycrystalline, wafer-scale MoS2, TiS2, and WS2 films of controlled thickness at record-low temperatures down to 100 °C using plasma-enhanced atomic layer deposition. We show that preventing excess sulfur incorporation from H2S-based plasma is the key to deposition of crystalline films, which can be achieved by adding H2 to the plasma feed gas. Film composition, crystallinity, growth, morphology, and electrical properties of MoSx films prepared within a broad range of deposition conditions have been systematically characterized. Film characteristics are correlated with results of field-effect transistors based on MoS2 films deposited at 100 °C. The capability to deposit MoS2 on poly(ethylene terephthalate) substrates showcases the potential of our process for flexible devices. Furthermore, the composition control achieved by tailoring plasma chemistry is relevant for all low-temperature plasma-enhanced deposition processes of metal chalcogenides.

Kinetic insights into plasma-assisted low-temperature oxidation of propane with synchrotron photoionization mass spectrometry

The present study investigates the chemical kinetics of low-temperature oxidation of propane activated by nanosecond pulsed dielectric barrier discharge in a flow reactor. Molecular beam mass spectrometry with tunable synchrotron vacuum ultraviolet photoionization (SVUV-PIMS) is employed for components identification and quantification. A series of hydrocarbons and oxygenated intermediates are observed, including fuel-specific species reported for the first time in this system like propyl hydroperoxide (C3H7OOH), acrolein (C3H4O2), oxetane (-CH2CH2CH2O-), methyloxirane (-CH(CH3)CH2O-), and propanol (n-/i-C3H7OH), which provide original kinetic information in the plasma-assisted low-temperature oxidation of propane. The detection of alkyl hydroperoxide (ROOH) demonstrates the existence of alkyl peroxy (RO2) formed through oxygen addition to alkyl (R) and the detection of cyclic ethers provides evidence for the presence of hydroperoxyl alkyl (QOOH). A kinetic model incorporating plasma chemistry and combustion chemistry is developed for plasma-assisted oxidation of propane. Path fluxes of fuel consumption and oxygenated intermediates formation are provided based on model analysis. Besides H abstractions by the OH radical, reactions activated by plasma involving electron impact dissociation, O(1D)/Ar* quenching dissociation, and ionization contribute much to fuel consumption. The formed propyl (n-/i-C3H7) are exclusively consumed through oxygen addition producing propyl peroxy (n-/i-C3H7O2). Propyl peroxy can participate in self- and cross-reactions yielding various oxygenated intermediates such as aldehydes, ketones, alcohols, and propoxy (n-/i-C3H7O). Discrepancies between simulations and experiments suggest that further kinetic studies on low-temperature mechanisms, including propyl peroxy related reactions for plasma-assisted combustion modeling, are still desired.

Combined application of online FIGAERO-CIMS and offline LC-Orbitrap mass spectrometry (MS) to characterize the chemical composition of secondary organic aerosol (SOA) in smog chamber studies

Abstract. A combination of online and offline mass spectrometric techniques was used to characterize the chemical composition of secondary organic aerosol (SOA) generated from the photooxidation of α-pinene in an atmospheric simulation chamber. The filter inlet for gases and aerosols (FIGAERO) coupled with a high-resolution time-of-flight iodide chemical ionization mass spectrometer (I−-ToF-CIMS) was employed to track the evolution of gaseous and particulate components. Extracts of aerosol particles sampled onto a filter at the end of each experiment were analysed using ultra-performance liquid chromatography ultra-high-resolution tandem mass spectrometry (LC-Orbitrap MS). Each technique was used to investigate the major SOA elemental group contributions in each system. The online CIMS particle-phase measurements show that organic species containing exclusively carbon, hydrogen, and oxygen (CHO group) dominate the contribution to the ion signals from the SOA products, broadly consistent with the LC-Orbitrap MS negative mode analysis, which was better able to identify the sulfur-containing fraction. An increased abundance of high-carbon-number (nC≥16) compounds additionally containing nitrogen (CHON group) was detected in the LC-Orbitrap MS positive ionization mode, indicating a fraction missed by the negative-mode and CIMS measurements. Time series of gas-phase and particle-phase oxidation products provided by online measurements allowed investigation of the gas-phase chemistry of those products by hierarchical clustering analysis to assess the phase partitioning of individual molecular compositions. The particle-phase clustering was used to inform the selection of components for targeted structural analysis of the offline samples. Saturation concentrations derived from nearly simultaneous gaseous and particulate measurements of the same ions by FIGAERO-CIMS were compared with those estimated from the molecular structure based on the LC-Orbitrap MS measurements to interpret the component partitioning behaviour. This paper explores the insight brought to the interpretation of SOA chemical composition by the combined application of online FIGAERO-CIMS and offline LC-Orbitrap MS analytical techniques.

A Global Model Study of Plasma Chemistry and Propulsion Parameters of a Gridded Ion Thruster Using Argon as Propellant

This work reports on the (zero-dimensional) global model study of argon plasma chemistry for a cylindrical thruster based on inductively coupled plasma (ICP) whose output has a system of two grids polarized with each other with direct current potential. The global model developed is based on particle and energy balance equations, where the latter considers both charged and neutral species. Thus, the model allows the determination of the neutral gas temperature. Finally, this study also investigated the role of excited species in plasma chemistry especially in the ions production and its implications for propulsion parameters, such as thrust. For this, the study was carried out in two different scenarios: (1) one taking into account the metastable species Arr and Arp (multi-step ionization), and (2) the other without these species (single-step ionization). Results indicates a distinct behavior of electron temperature with radiofrequency (RF) power for the investigated cases. On the other hand, the gas temperature is almost the same for investigated power range of up to 900 W. Concern propulsion analysis, a thrust of 40 mN at 450 W was verified for case (1), which represents a remarkable thrust value for electric thrusters.

Collision Cross-Section Measurements of Collision-Induced Dissociation Precursor and Product Ions in an FTICR-MS and an IM-MS: A Comparative Study.

Sustained off-resonance irradiation-cross-sectional areas by Fourier transform ion cyclotron resonance mass spectrometry (SORI-CRAFTI) is an FTICR-MS strategy to collisionally activate precursor ions and then measure their ion-neutral collision cross sections, as well as those of selected products, at the same time. We benchmarked SORI-CRAFTI using protonated leucine-enkephalin, to excellent agreement (typically within 1-2%) with previous studies performed via collision-induced dissociation-ion mobility (CID-IMS). SORI-CRAFTI was then applied to alkali metal-cationized leucine-enkephalin and compared with CID-IMS via precursor/product cross-section ratios. Qualitative agreement between SORI-CRAFTI and CID-IMS was excellent (again, usually within 1-2%); however, neither SORI-CRAFTI nor CID-IMS could determine if metalated leucine-enkephalin was present in its canonical or zwitterionic form. When SORI-CRAFTI was used on [2.2.2]-cryptand+Cs+, SORI activation resulted in a 5% decrease in collision cross section, consistent with migration of the externally bound Cs+ into the cryptand's cavity and similar to the cross section observed when electrospraying from an isopropanol-rich solvent. Thus, SORI-CRAFTI is useful for studying gas-phase ion chemistry of small- to medium-sized molecules and host-guest systems.

Perspectives of Gas Phase Ion Chemistry: Spectroscopy and Modeling

The study of ions in the gas phase has a long history and has involved both chemists and physicists. The interplay of their competences with the use of very sophisticated commercial and/or homemade instrumentations and theoretical models has improved the knowledge of thermodynamics and kinetics of many chemical reactions, even if still many stages of these processes need to be fully understood. The new technologies and the novel free-electron laser facilities based on plasma acceleration open new opportunities to investigate the chemical reactions in some unrevealed fundamental aspects. The synchrotron light source can be put beside the FELs, and by mass spectrometric techniques and spectroscopies coupled with versatile ion sources it is possible to really change the state of the art of the ion chemistry in different areas such as atmospheric and astro chemistry, plasma chemistry, biophysics, and interstellar medium (ISM). In this manuscript we review the works performed by a joint combination of the experimental studies of ion–molecule reactions with synchrotron radiation and theoretical models adapted and developed to the experimental evidence. The review concludes with the perspectives of ion–molecule reactions by using FEL instrumentations as well as pump probe measurements and the initial attempt in the development of more realistic theoretical models for the prospective improvement of our predictive capability.

Study and Numerical Simulation of Negative and Positive Corona Discharge: A Review

Two models to describe the phenomenon of corona discharge are presented: the first is known as the plasma model which with plasma chemistry defines the volumetric and surface reactions among charge carriers such as electrons, positive, and negative ions. This model uses Poisson's equation and a formulation of the space-charge density to calculate the electric field necessary to solve the species transport equations. Besides, only the plasma model determines the density of the charge carriers. The second is a simplified model which describes the corona discharge in terms of current conservation coupled with Poisson's equation. This model does not have any connection with the attributes of plasma chemistry. Both models propose solutions for the electric potential and space charge density distribution from the corona electrode to the ground electrode.