Inelastic Collisions Of Electrons Research Articles

Self-consistent modeling and analysis of spatial homogeneity of pure Na and Na−Ar mixture resonance photoplasma in a gas cell for Voigt profile

A self-consistent modeling of the resonance photoplasma in pure Na and Na−Ar mixtures with spatial homogeneity of photoexcitation of the resonance levels of Na in the volume of a cylindrical gas cell has been carried out. The Voigt line shape and the collision broadening of the D1 and D2 lines of Na were considered. The main photoplasma parameters were calculated for the Na pressure PNa=0.0045−0.165 torr, the PAr/PNa=0 and 10k (k = 1, 2 and 3) values and the gas temperature of 680 K at the pumping resonance radiation flux density F = 40 W/(m2nm). It has been established that the electron density Ne and temperature Te increase non-linearly with the growth of the PNa and reach, respectively, 6.4·1018 m−3 at PNa=0.165 torr and PAr/PNa=100 and 0.28 eV for the pure Na photoplasma. Herewith, the dependence of Te on the Ar pressure PAr is non-monotonic. It is a consequence of the cooperative action of electron inelastic collisions of the first and second kinds with Na atoms and elastic collisions with Na and Ar atoms. The comparison of the obtained results for the L = 4R = 0.02 m case with those calculated for the infinite cylinder case with the same R value showed the good validity of the infinite cylinder approximation. As a result of our analysis of the quenching of the resonance levels and theoretical results from the literature, it has been established that the spatial non-homogeneity of the investigated photoplasma caused by this quenching does not exceed 20 % for the PNa≤0.1 torr and PAr/PNa=0 − 103. The obtained data can be used in studies of alkali-containing photoplasmas and to create photoelectric converters based on them.

Estimation of electron density, temperature and electrical characterization of silica seeded arc plasma at atmospheric pressure

Plasma technology stands at the forefront of numerous industrial applications, offering versatile solutions from materials processing to aerospace engineering. This study employs a single Langmuir probe technique operating at atmospheric pressure to scrutinize the transformative impact of silica seeding on low-temperature arc plasma. The investigation unveils a dynamic interplay of electrons and ions within the plasma, unveiling key electrical properties. The I–V electrical properties of the arcs plasma before seeding, having a floating voltage of –39 V, demonstrate electron and ion currents for varied probe voltages. The electrons’ density is calculated to be 2.11×1013 m–3, and the electrons’ temperature is at 6.25 eV. The I–V characteristics show a floating potential of about –35 V and –37 V after seeding an arc plasma using silica in the presence of aluminum oxide (2 % by weight) powder and grain, respectively. After seeding, it is discovered that the electron temperature falls to 1.18 eV for powder while 1.16 eV for grain and electron density rises to 2×1016 m–3 for powder and 1.84×1016 m–3 for grain. In addition, a notable fall in electron temperature and a discernible rise in electron density are seen. This non-equilibrium behavior is related to silica’s catalytic function, which is enhanced by the presence of aluminum oxide. Additionally, increased ionizing activity brought on by inelastic electron collisions causes the electron temperatures in the silica-seeded arcs plasma to rise with discharge voltage. These findings can be essential for enhancing plasma-based technologies in a variety of industrial applications because they provide insightful information on how silica seeding affects arc plasma properties

Evaluation of the effectiveness of energetic thermal electrons on the excitation of the ionospheric red 6300 Å airglow

In this paper we use previously calculated ionosphere electron temperatures Te in order to estimate the 6300 Å (red) airglow intensity enhancements attributed to thermal electrons from the tail of a Maxwellian electron distribution of sufficiently increased electron temperature. Then, we compare our results with the relevant observed measurements and we comment on the quality of the comparison and the possible causes of the differences. We also calculate the airglow intensity characteristic rise and decay times and compare them to the experimental ones, and we investigate the origin of the electrons which excite the red airglow. In the end, we assess the departure of the ionosphere electron energy distribution from a purely Maxwellian one, and the role of the electron elastic and inelastic collisions with the other components of the ionospheric F-region.

Analytical Formulas for Approximating Cross Sections of Electron Collisions with Hydrogen, Noble Gases, Alkali and Other Atoms

This paper presents an analysis of data on the cross sections of elastic and inelastic collisions of electrons with noble gases, alkali and other atoms. For the selected sets of experimental and theoretical data, optimal analytical formulas are found, and approximation coefficients are calculated. The obtained semi-empirical formulas reproduce the values of the transport (diffusion), excitation and ionization cross sections for noble gases. Much attention is paid to the ionization cross sections of metal atoms, which are often present as an impurity in gas-discharge plasma. The approximation formulas reproduce the values of the ionization cross sections for hydrogen, metal and other elements in a wide range of energies with accurate orders of errors of the available theoretical and experimental data. For some elements with a two-hump plot of the dependence of the ionization cross section on the collision energy, it is proposed to use a two-term formula that takes into account ionization from both external and internal shells.

Inclusion of Electron Interactions by Rate Equations in Chemical Models

The concept of treating subranges of the electron energy spectrum as species in chemical models is investigated. This is intended to facilitate simple modification of chemical models by incorporating the electron interactions as additional rate equations. It is anticipated that this embedding of fine details of the energy dependence of the electron interactions into rate equations will yield an improvement in computational efficiency compared to other methods. It will be applicable in situations where the electron density is low enough that the electron interactions with chemical species are significant compared to electron–electron interactions. A target application is the simulation of electron processes in the D-region of the Earth’s atmosphere, but it is anticipated that the method would be useful in other areas, including enhancement of Monte Carlo simulation of electron–liquid interactions and simulations of chemical reactions and radical generation induced by electrons and positrons in biomolecular systems. The aim here is to investigate the accuracy and practicality of the method. In particular, energy must be conserved, while the number of subranges should be small to reduce computation time and their distribution should be logarithmic in order to represent processes over a wide range of electron energies. The method is applied here to the interaction by inelastic and superelastic collisions of electrons with a gas of molecules with only one excited vibrational level. While this is unphysical, it allows the method to be validated by checking for accuracy, energy conservation, maintenance of equilibrium and evolution of a Maxwellian electron spectrum.

Laser Probing of the Rotational Cooling of Molecular Ions by Electron Collisions.

We present state-selected measurements of rotational cooling and excitation rates of CH^{+} molecular ions by inelastic electron collisions. The experiments are carried out at a cryogenic storage ring, making use of a monoenergetic electron beam at matched velocity in combination with state-sensitive laser dissociation of the CH^{+} ions for simultaneous monitoring of the rotational level populations. Employing storage times of up to 600s, we create conditions where electron-induced cooling to the J=0 ground state dominates over radiative relaxation, allowing for the experimental determination of inelastic electron collision rates to benchmark state-of-the-art theoretical calculations. On a broader scale, our experiments pave the way to probe inelastic electron collisions for a variety of molecular ions relevant in various plasma environments.

Synchronising optical emission spectroscopy to spokes in magnetron sputtering discharges

Spokes are patterns of increased light emission, observed to rotate in front of the targets of magnetron sputtering discharges. They move through the plasma at velocities of several km s−1 in or against the direction of the discharge. The high velocity and their initial creation at arbitrary positions render measurements of spokes challenging. For more demanding plasma diagnostic techniques that require data acquisition over multiple discharge pulses, synchronisation to the spoke movement is necessary. In this publication, we present optical emission spectroscopy of spokes in both high power impulse magnetron sputtering (HiPIMS) as well as direct current magnetron sputtering (DCMS) discharges, performed by triggering a camera on the spoke movement. Optical filters between plasma and camera allow us to isolate emission lines of metal and working gas neutrals and ions. Based on these optical measurements and previous probe studies, the dynamics of electrons drifting through spokes in both DCMS and HiPIMS is discussed. In HiPIMS, the much shorter mean free path for inelastic electron collisions enables strong ionisation inside the spoke, causing a sudden variation in electron density which leads to the distinct spoke shape. In contrast, the spoke shape for DCMS discharges seems to rather be indicative of electron energy variations.

Analytical approximation of cross sections of collisions of electrons with atoms of inert gases

The paper presents an analysis of data on the cross sections of elastic and inelastic collisions of electrons with noble gas atoms. The transport (diffusion) cross sec-tion, the excitation and ionization cross sections are considered. For the selected sets of experimental and theoretical data, optimal analytical formulas are found and approximation coefficients are selected for them. The obtained semi-empirical formulas allow us to reproduce the cross section values in a wide range of colli-sion energies from 0.001 to 10000 eV with an accuracy of several percent.

Cross sections of electron collisions with noble gases atoms

Consideration is given to the analysis of data on the cross sections of elastic and inelastic col-lisions of electrons with noble gas atoms. The transport (diffusion) cross section, the excita-tion and ionization cross sections are studied. For the selected sets of experimental and theo-retical data, optimal analytical formulas are found and approximation coefficients are select-ed for them. The obtained semi-empirical formulas allow us to reproduce the cross section values in a wide range of collision energies from 0.001 to 10000 eV with an accuracy of sev-eral percent.

Elastic and electronically inelastic electron collisions by the thiophene molecule

Differential and integral cross sections for elastic and electronically inelastic scattering of electrons by the thiophene molecule were determined by means of the Schwinger multichannel method within the static-exchange plus polarization approximation in the energy range from 3.41 to 50 eV. We investigated the influence of multichannel coupling effects by calculating the cross sections according to different schemes of channel coupling that range from 1 to 61 open channels along with polarization effects, depending on the energy considered. The comparison of these results shows that the inclusion of more channels in the scattering calculations leads to a significant decrease in the magnitude of the cross sections. Present results corresponding to our best level of channel coupling at a given energy, both for elastic and electronically inelastic electron scattering by thiophene, display an overall good agreement with the data available in the literature.

First-Principles Study on Electron-Induced Excitations of Atomic Layer Deposition Precursors: Inelastic Electron Wave Packet Scattering with Cobalt Tricarbonyl Nitrosyl Co(CO)3NO Using Time-Dependent Density Functional Theory.

A quantitative study on inelastic electron scattering with a molecule is of significant importance for understanding the essential mechanisms of electron-induced gas-phase and surface chemical reactions in their excited electronic states. A key issue to be addressed is the quantitatively detailed inelastic electron collision processes with a realistic molecular target, associated with electron excitation that leads to potential ionization and dissociation reactions of the molecule. Using the real-time time-dependent density functional theory (TDDFT) modeling, we present quantitative findings on the energy transfers and internal excitations for the low energy (up to 270 eV) electron wave packet impact with the molecular target cobalt tricarbonyl nitrosyl (CTN, Co(CO)3NO) that is used as a precursor in electron-enhanced atomic layer deposition (EE-ALD) growth of Co films. Our modeling shows the quantitative dependence of the wave packet sizes, target molecule orientations, and impact parameters on the energy transfer in this inelastic electron scattering process. It is found that the wave packet sizes have little effect on the overall profile of the internal multiple excited states, whereas different target orientations can cause significantly different internal excited states. To evaluate the quantitative prediction capability, the inelastic scattering cross-section of a hydrogen atom is calculated and compared with the experimental data, leading to a constant scaling factor over the whole energy range. The present study demonstrates the remarkable potential of TDDFT for simulating the inelastic electron scattering process, which provides critical information for future exploration of electronic excitations in a wide range of electron-induced chemical reactions in current technological applications.

Optical dispersion equations for metals applicable to the Far-IR through EUV spectral range

The long-standing problem of finding a general formulation of optical dispersion for metals, valid over a wide spectral range of photon energy E is tackled. To this end, equations for refractive index n and extinction coefficient k as functions of E are developed. Functions and respectively represent real and imaginary parts of complex index of refraction Previous formulations, most of which are based on various combinations of Drude and Lorentz models, are either useable only over a limited spectral range or do not accurately fit experimental data. The formulation overcomes these shortcomings by exploiting concepts set forth by Forouhi and Bloomer in 1986, 1988 and 2019 publications pertaining to optical dispersion of semiconductors and insulators. These concepts are centered on time-dependent perturbation theory and consistency with principle of causality. The new expression for is based on three types of events initiated by photon-electron interactions in metals: intraband electron dipole transitions; interband electron dipole transitions; inelastic collisions of electrons. Expression for is obtained as Hilbert transform of It is demonstrated that the new dispersion equations satisfy Titchmarsh’s Theorem, a mathematical theorem that conveys the principle of causality, which in turn establishes the theoretical validity of the formulation. Equations for and are fitted to published experimental data of metals encompassing all metal groups of the periodic table. Reported data span various ranges of energy, from far-infrared to extreme-ultraviolet. Excellent fits between calculated and experimental spectra are achieved. Having established consistency with Titchmarsh’s Theorem and by extension, causality, plus agreement with experimental findings suggests this formulation represents a valid description of optical dispersion of metals.

Electronic excitation of the 3B2 state of thiophene molecule by low-energy electron collisions

The Schwinger multichannel method is employed to study elastic and electronically inelastic collisions of low-energy electrons by the thiophene molecule. It is well known that the elastic integral cross section for electron-thiophene scattering presents three shape resonances, some of which located around the opening region of the first excited state. The main purpose of this work is to evaluate the influence of polarization effects on the positions of the resonances appearing in the elastic channel and its potential impact on the description of the electronic excitation process involving the transition from ground state to the 3B2 excited state of thiophene. Our cross section results indicate that target polarization may affect the electronic excitation process in the region of the threshold of the 3B2 excited state, but its impact seems to be related to the effect of polarization on the resonances in the elastic channel. More specifically, there are cases (A2 and B1 symmetries) where the overlap of the shape resonance with the threshold changes significantly with the inclusion of polarization resulting in a considerable modification in the magnitude of the electronically inelastic cross section, while in other case (B2 symmetry) a similar overlap is not accompanied by sensible changes in the magnitude of the excitation cross section. Our excitation functions at scattering angles of 90° and 135° are compared with the calculations and measurements of Loupas et al (2018 J. Phys. Chem. A 122 1146) and show in general a qualitative agreement.

Electron collision cross section set of Cl2 gas and electron transport analysis in Cl2 gas and Cl2/N2 mixtures

A detailed and reliable electron collision cross section set of Cl2 gas is constructed. The present cross section set consists of one elastic momentum transfer, three vibrational excitation, eight dissociative electronic excitation, two electronic excitation, one ion-pair formation, one dissociative electron attachment, and four ionization cross sections. The electron drift velocity, longitudinal diffusion coefficient, ionization coefficient, and electron attachment coefficient in both Cl2 gas and Cl2/N2 mixtures and the electron attachment rate coefficient in mixtures of N2 gas and a minute amount of Cl2 gas are calculated by Monte Carlo simulation using the present cross section set, and then the reliability of the present cross section set is demonstrated by comparing calculated and measured electron transport coefficients and rate coefficients. Furthermore, the rate coefficients for both elastic and inelastic electron collisions and the mean energy of electrons in Cl2 gas are calculated from the present cross section set and are provided.

Elastic and inelastic low-energy electron collisions with PH2, PF2 and PCl2 radicals

Ab initio scattering calculations for low-energy electron collisions with PH2, PF2, and PCl2 are performed using the R-matrix method in this study. The elastic integral, differential, and momentum transfer cross sections and the excitation cross sections from the ground state to the five low-lying electron excited states are presented in the energy region of 0.01–15 eV. The target states are represented by including correlations via a configuration interaction technique. The resonant states are detected and identified. The sensitivity of the results to changes in the theoretical model is checked by comparing predictions from a variety of approximations including static exchange, one state close-coupling (CC), and many-state CC approximations. The similarities and differences among the resonances of these three radicals are discussed.

Experimental and PIC MCC study of electron cooling—re-heating and plasma density decay in low pressure rf ccp argon afterglow

In this work, experimental and theoretical study of pulsed discharge in argon has been carried out. The experimental data on the dynamics of electron density, electron temperature, and plasma potential have been obtained by probe measurements (using hairpin and Langmuir probes) in the afterglow between two RF pulses. This dynamics is thoroughly analyzed by comparison with the results of the kinetic PIC MC simulations. The main processes that cause electron cooling have been revealed for two different time stages. The first afterglow stage is characterized by the rapid decrease of the electron temperature. During this stage, inelastic electron collisions with Ar atoms in the ground state play an important role in the electron cooling. During the second long-scale stage, only diffusion along the electron energy scale via Coulomb or elastic collisions can provide the observed effect of the gradual electron cooling. The effects of elastic and Coulomb collisions on the electron cooling have been separated and analyzed by means of PIC MC simulations. The temporal evolution of the electron concentration spatial distribution and the plasma boundary sheaths size has been also analyzed on the base of 1D PIC MC simulations. A good agreement between the probe measurements and the PIC simulations data on plasma density, ambipolar potential and electron temperature is observed. To perform a more detailed study of EEDF and electron temperature dynamics, the relative intensity of Ar(2p1) → Ar(1s2) emission at 750 nm has been measured. A very good agreement between the measured emission intensity and the calculated excitation rate of Ar(2p1) at different time scales validates the electron temperature temporal dynamics obtained by the used PIC model.

Role of Collisions with Neutrals in the Process of Modulational Excitation of Dust Acoustic Perturbations in Dusty Ionosphere

The role of inelastic collisions of electrons and ions with neutrals during the development of modulational instability involving dust acoustic perturbations in dusty ionospheric plasma, as well as the effect of collisions of electrons, ions, and dust grains with neutrals on the manifestations of modulational interaction in the dusty ionosphere, are estimated. It is shown that, in this case, the influence of collisions of electrons and ions with neutrals is usually less significant than the influence of collisions between dust grains and neutrals. It is demonstrated that the effect of modulational instability on the propagation of electromagnetic waves in the dusty ionospheric plasma is the most significant at altitudes of 100–120 km. The modulational interaction in the dusty ionosphere is important for the explanation of such effects as ground-based observations of low-frequency ionospheric radio noises with frequencies below 50 Hz, generation of infrasonic waves in the ionosphere and the possibility to detect them near the Earth’s surface, enhancement of the green nightglow emission at a wavelength of 557.7 nm from the lower ionosphere layer at altitudes of 110–120 km, and modulational excitation of inhomogeneities in the electron and ion densities in the ionosphere at altitudes of 100–120 km. The absence of observations of low-frequency ionospheric radio noise during such phenomena as noctilucent clouds and polar mesosphere summer echoes caused by the presence of dusty plasma at altitudes of 80–95 km is explained. It is shown that the latter phenomenon is related to the suppression of modulational processes at these altitudes.

Axial diagnosis of electron and negative ion behaviors in capacitively coupled O2-containing Ar plasma driven by 27.12 MHz

Capacitively coupled O2-containing Ar plasma driven by a radio frequency (RF) of 27.12 MHz has been investigated. The electron energy probability function (EEPF) was measured with a Langmuir probe. The electronegativity was measured with a laser-induced photodetachment (LIPD) technique in combination with a Langmuir probe. The probe measurement results show a transition of the EEPF from bi-Maxwellian to single-Maxwellian and finally to a Druyvesteyn distribution as RF input power or discharge pressure was increased. This transition indicates the evolution of the heating mode in the Ar plasma by changing the discharge conditions. Adding electronegative O2 gas into Ar plasma leads to the deviation of the EEPF from the pure Ar plasma case. This deviation becomes more serious at high pressure due to the inelastic collisions of electrons with oxygen molecules. Additionally, the addition of O2 not only lowers the electron density in the axial direction but also smoothens the electron density distribution close to the powered electrode in comparison to the linear electron density with the axis in the Ar plasma case. LIPD measurement results show that electronegativity in 5% O2-containing Ar plasma tends to be high as close to the powered electrode and to be a V-shaped distribution along the axis direction with the increase in the pressure. This behavior of the negative ion distribution may be caused by the combined effects of recombination of negative and positive ions and the pseudo-γ mode of negative ions with oxygen neutrals.

Inelastic Processes in a Gas-Discharge Plasma of Inert Gases

The excitation rate constants of the lower excited states of inert gas atoms by electron impact in the gas-discharge plasma are determined with taking into account the self-consistent character of this process and the rates of similar processes in the plasma of alkali metals. The rate constants of the stepwise ionization in a uniform gas-discharge plasma of inert gases are determined. They are also determined in a nonunifom plasma if the nonuniformity is a result of the passage of a gas-discharge current. Based on the rates of these processes, the populations of lower excited levels are calculated in the case where the equilibrium in the gas-discharge plasma of inert gases is determined by inelastic collisions of electrons with atoms.

Parameters of plasma of high-current nanosecond discharge in air with small admixtures of copper vapor

Introduction . The use of a discharge in air of atmospheric pressure opens the possibility of developing windowless UV lamps that are promising for applications with significant mechanical overloads under various extreme conditions, since they do not contain any quartz elements (windows or bulbs). The output characteristics of such point lamps strongly depend on the plasma parameters of the nanosecond discharge with small admixtures of the vapor metal from which the electrodes are made. At present, there are no data on the parameters of air plasma with small admixtures of copper vapor under the operating conditions of a point lamp, which inhibits the establishment of mechanisms for populating the excited levels of atoms and copper ions in such a plasma. This in turn inhibits the long-range optimization of the output characteristics of such point sources of UV radiation. Purpose . The purpose of the study was to determine the emission characteristics in the spectral range of 200-250 nm of the plasma of high-current nanosecond discharge, between copper electrodes in air at atmospheric pressure under conditions of strong overstress of the discharge gap and to carry out a numerical simulation of the parameters of the plasma of air with small copper impurities under conditions close to those realized in the experiment. Methods . The nanosecond discharge in air of atmospheric pressure between copper electrodes was ignited. The distance between the copper electrodes was 1 mm, which led to the ignition at atmospheric pressure air of a point diffuse discharge of a spherical shape with a diameter of 1 mm. The standard program was used to solve the Boltzmann kinetic equation for the electron energy distribution function (EEDF) for modeling air plasma atmospheric pressure parameters with small copper vapor admixtures, since under the experimental conditions the maximum value of the E/P parameter reached about 530 V cm -1 torr -1 , which is less than the critical value of E/P for nitrogen according to the local electron runaway criterion – 590 V cm -1 torr -1 . Results . Numerical simulation of the plasma parameters established that for the range of reduced electric field strength 610 Td-810 Td, at which experimental studies of the characteristics of a point nanosecond discharge were carried out, mean electron energies varied within the range of 12.2 -15.6 eV; the value of the electron concentration was 10.7·10 21 m -3 – 8.7 ·10 21 m -3 at a current density of 765 · 10 6 A / m 2 on the surface of the copper electrode. The excitation constants of the 2 P 3/2, 1/2 , 2 D 3/2 , 2 D 5/2 , 4 F 7/2 , - states of the copper atom and its ionization were in the range (7.3 – 8.5) 10 -13 m 3 /c, ( 0.29 - 0.28) 10 -13 m 3 /c, ( 0.22 - 0.22) 10 -13 m 3 /c, (0.19 – 0.22) 10 -15 m 3 /c and (0.33 -0.45) 10 -13 m 3 /c,, respectively. The maximum excitation rate constant for nitrogen molecules was for the sum of the singlet states: they were (1.4 10 -14 ) m 3 / s for an electric field strength of 810 Td. The specific losses of the discharge power in the plasma on inelastic collisions of electrons with the components of the gas mixture were maximal for nitrogen molecules and reached 32% for excitation of the sum of singlet nitrogen states. Conclusion . Radiation of the plasma is concentrated in a narrow spectral interval of 200-250 nm, is promising for use as a point UV lamp; the spectral lines 248.9 and 254.4 nm Cu II are promising for estimating the electron temperature in a plasma. Mean electron energy, electron mobility, specific electric power losses and the rate constants of elastic and inelastic scattering of electrons by copper, argon and carbon dioxide, oxygen and nitrogen molecules, the ratio of which was 3: 7.098: 0.266: 159.157: 593.438, depending on the magnitude of the reduced electric field (ratio of the electric field strength (E) to the total concentration of atoms and gas molecules (N)). The range of changes in the parameter E / N = 1-1300 Td (1 ∙10 -17 - 1 ∙ 10 -15 V ∙ cm 2 ) and included the values of the parameter E / N, which were realized in the experiment (610-810) Td.