Electron Collision Cross Sections Research Articles

R-matrix calculations of differential and integral cross sections for low-energy electron collisions with ethanol

Electron collisions with C2H5OH are studied up to impact energies of 10 eV using several theoretical models. Calculated differential cross sections suggest that the extrapolation to low angles used to extend experimental data and hence give integral cross sections significantly underestimates the large, dipole-driven forward scattering cross section. An improved set of values for the rotationally-unresolved elastic cross section is proposed; the corresponding rotationally resolved cross sections are also presented. Static exchange plus polarisation calculations find a very broad shape resonance in each of the 2A′ and 2A′′ symmetries in the 7 eV collision region however no resonance at lower energies, in qualitative agreement with the interpretation of some but not all dissociative electron attachment measurements.

Electron collision cross sections for the TMS molecule and electron transport coefficients in TMS-Ar and TMS-O2 mixtures

A consistent set of low-energy electron-collision cross sections for the tetramethylsilane (TMS) molecule has been derived from the measured electron transport coefficients for a pure TMS molecule by using an electron swarm study and a two-term approximation of the Boltzmann equation for energy. The electron transport coefficients, which were calculated by using the derived set, are consistent with the experimental data over a wide range of E/N values (ratio of the electric field E to the neutral number density N). The present set of electron collision cross sections for the TMS molecule, therefore, is the best available so far for quantitative numerical modeling of plasma discharges for processing procedures with materials containing TMS molecules. The electron-transport coefficients in TMS-Ar and TMS-O2 mixtures were also calculated and analyzed in a wide range of E/N ratios for the first time. The presence of a remarkable synergism in the Townsend first ionization coefficient has been pointed out in the TMS-O2 mixtures.

Monte Carlo simulation of the electron beam scattering under water vapor environment at low energy

This paper reports on Monte Carlo simulations of electrons propagation in water vapor using a set of electron collision cross sections created with data published recently in order to follow the beam profile at low energy in environmental scanning electron microscopy (ESEM). Results show that lowering electrons beam energy or pressure has little effect on the skirt extend which is mainly function of working distance. The ionization and excitation events per track history are independent of the initial electron energy in the 1–5 keV range. Ionization occurs with low energy electrons, frequently above 50 eV, whereas the excitation processes are dominated by the electrons below 50 eV.

Electron Collision Cross Sections for the Tetraethoxysilane Molecule and Electron Transport Coefficients in Tetraethoxysilane–O2 and Tetraethoxysilane–Ar Mixtures

A consistent set of low energy electron collision cross sections for tetraethoxysilane (TEOS) molecule has been derived from the measured electron transport coefficients (electron drift velocity W , density-normalized longitudinal diffusion coefficient ND L , ratio of the longitudinal diffusion coefficient to the electron mobility D L /µ, and Townsend first ionization coefficient α/ N ) in pure TEOS molecule and those calculated by using an electron swarm study and a two-term approximation of the Boltzmann equation for energy. The electron transport coefficients calculated using the derived set are consistent with the experimental data over a wide range of E / N values (ratio of the electric field E to the neutral number density N ). The present set of electron collision cross sections for the TEOS molecule, therefore, is the best available so far for quantitative numerical modeling plasma discharges for processing procedures with materials containing TEOS molecules. Electron transport coefficients in TEO...

Elastic and inelastic cross sections for low-energy electron collisions with pyrimidine

We present theoretical elastic and electronic excitation cross sections and experimental electronic excitation cross sections for electron collisions with pyrimidine. We use the R-matrix method to determine elastic integral and differential cross sections and integral inelastic cross sections for energies up to 15 eV. The experimental inelastic cross sections have been determined in the 15-50 eV impact energy range. Typically, there is quite reasonable agreement between the theoretical and experimental integral inelastic cross sections. Calculated elastic cross sections agree very well with prior results.

Electric and Spectroscopic Analysis of Surface Corona Discharges in Ambient Air and Comparison With Volume Corona Discharges

This paper is firstly devoted to experimental electrical analysis of a dc surface corona discharge in ambient air at atmospheric pressure and room temperature. The surface corona discharge is established between a positive pin and a grounded plate electrode, set on the same side of an insulating plate made either in polymethyl methacrylate (PMMA) or in polytetrafluoroethylen (PTFE). The interelectrode distance, the tip radius of the pin, the applied voltage to the pin, and the nature of the dielectric have been parameterized, and discharge currents are analyzed. It is shown for instance that the surface corona discharge can be ignited over a PMMA dielectric for an applied voltage 20% lower than the PTFE case. This is coherent with calculations of electric fields which are, in the pin region, 25% higher over PMMA than over PTFE. Electrical characteristics of dc surface corona discharge are then compared with those obtained in the case of volume corona discharges generated in the same ambient atmospheric air by using the same positive pin in front of a copper cathode plane. It is observed for the same conditions (applied voltage, gap distance, and tip radius) that the surface corona discharge develops with a higher discharge current even if the UV-visible spectra of both surface and corona discharges remain quasi-similar. This better electric efficiency of surface corona discharge in comparison to volume corona is confirmed from calculations of electric fields and corresponding production rates of certain active species near the pin using multiterm Boltzmann equation solution and literature electron-molecule collision cross sections for electrons impacts with ambient air.

Cross sections for electron collision with five-membered ring heterocycles

The absolute total cross-section (TCS) for electron scattering from isoxasole, (CH)3NO, molecule has been measured using the linear transmission technique for impact energies ranging from 1 to 400 eV. The measured TCS energy dependence appears typical for highly polar targets; over whole energy range applied, the magnitude of TCS generally decreases as the energy increases. Some narrow features located near 1.2 and 2.7 eV have been observed in the TCS curve as well as a broad enhancement spanned between 5 and 15 eV. The TCS for electron-isoxazole scattering has been compared with TCS data for furan, (CH)4O; differences and similarities in the appearance of both TCSs energy functions are indicated and discussed. In addition, for several five-membered ring heterocycle molecules: isoxazole, pyrrole [(CH)4NH] and tiophene [(CH)4S], integral elastic (ECS) and ionization (ICS) cross sections have been calculated at intermediate and high electron-impact energies in the additivity rule approximation and the binary-encounter-Bethe approach, respectively. For isoxazole and furan the sums of ECS and ICS are in very good agreement with the respective measured TCSs above 50 − 60 eV.

Cross sections for elastic electron scattering by tetramethylsilane in the intermediate-energy range

Organosilicon compounds are of current interest due to the numerous applications of these species in industries. Some of these applications require the knowledge of electron collision cross sections, which are scarce for such compounds. In this work, we report absolute values of differential, integral, and momentum-transfer cross sections for elastic electron scattering by tetramethylsilane (TMS) measured in the 100-1000 eV energy range. The relative-flow technique is used to normalize our data. In addition, the independent-atom-model (IAM) and the additivity rule (AR), widely used to model electron collisions with light hydrocarbons, are also applied for e{sup -}-TMS interaction. The comparison of our measured results of cross sections and the calculated data shows good agreement, particularly near the higher-end of incident energies.

Resonances in electron collisions with C2H2Cl2 isomers

We present elastic cross sections for low-energy electron collisions with the isomers of C2H2Cl2 molecule, namely 1,1-dichloroethylene, cis-1,2-dichloroethylene and trans-1,2-dichloroethylene. To compute the cross sections, we employed the Schwinger multichannel method with pseudopotentials in the static exchange and in the static-exchange plus polarization approximations for energies up to 40 eV. We found π* and σ* shape resonances in the cross sections of the three isomers, with positions in relative agreement with the results reported by Burrow et al (1981 Chem. Phys. Lett. 82 270) for the vertical attachment energies. We also carried out electronic structure calculations in order to help in the characterization of these resonances. We found a Ramsauer–Townsend minimum in the cross section of trans-1,2-dichloroethylene at 0.1 eV.

Elastic collisions of low-energy electrons with SiY4(Y=Cl, Br, I) molecules

We employed the Schwinger multichannel method to compute elastic integral, differential, and momentum transfer cross sections for low-energy electron collisions with Si$Y$${}_{4}$ ($Y$ $=$ Cl, Br, I) molecules. The calculations were carried out in the static-exchange and static-exchange plus polarization approximations for energies up to 10 eV. The elastic integral cross section for SiCl${}_{4}$ and SiBr${}_{4}$, computed in the static-exchange plus polarization approximation, shows two shape resonances belonging to the ${T}_{2}$ and $E$ symmetries of the ${T}_{d}$ group, and for SiI${}_{4}$ shows one shape resonance belonging to the $E$ symmetry of the ${T}_{d}$ group. The present results agree well in shape with experimental total cross sections. The positions of the resonances observed in the calculated integral cross sections are also in agreement with the experimental positions. We have found the presence of a virtual state for SiCl${}_{4}$ and a Ramsauer-Townsend minimum for SiI${}_{4}$ at 0.5 eV. The present results show that the proper inclusion of polarization effects is crucial in order to correctly describe the resonance spectra of these molecules and also to identify a Ramsauer-Townsend minimum for SiI${}_{4}$ and a virtual state for SiCl${}_{4}$.

Electron Transport Properties in HSi(OC2H5)3 Vapor

The electron swarm parameters in HSi(OC2H5)3 (triethoxysilane, TRIES) vapor have been investigated for relatively wide ranges of reduced electric field (E/N). Based on the arrival-time spectra (ATS) method for electrons using a double-shutter drift tube, the drift velocity and the longitudinal diffusion coefficient were measured for the E/N=20–5000 Td, and the ionization coefficient was obtained for E/N=300–5000 Td. The results were compared with those for SiH4 and Si(OC2H5)4 (tetraethoxysilane, TEOS), to show characteristics similar to the parameters in TEOS. We also determined the electron collision cross sections for TRIES by means of the Boltzmann equation analysis.

A set of cross sections and transport coefficients for electrons in HBr

We have compiled a set of electron collision cross sections for HBr. It will be useful for a fluid modeling of HBr plasmas together with transport coefficients in both DC and RF, E and E×B fields. The calculation made use of a Monte Carlo technique. The transport coefficients are rather unstructured because the total cross section resembles that of a constant collisonal frequency model. Additional measurements of swarm parameters are required in order to obtain more acurate set of cross sections.

Electron Collision Cross Sections for the Cl2 Molecule from Electron Transport Coefficients

The measured electron transport coefficients (electron drift velocity, Townsend first ionization coefficient, electron attachment coefficient, and density-normalized effective ionization coefficient) in pure Cl 2 have been analyzed to derive the currently best available electron collision cross section set of the elastic and inelastic electron collision cross sections for the Cl 2 molecule using an electron swarm study and a two-term approximation of the Boltzmann equation for energy. The electron transport coefficients calculated using the derived cross sections are consistent with the experimental data over a wide range of E / N values (ratio of the electric field E to the neutral number density N ). The present electron collision cross section set for the Cl 2 molecule is the best available so far for quantitative numerical modeling plasma discharges for processing procedures with materials containing Cl 2 molecules.

Absolute angle-differential elastic cross sections for electron collisions with diacetylene

We report measured and calculated differential elastic cross sections for collisions of low-energy electrons with diacetylene (1,3-butadiyne). A generally satisfactory agreement between theory and experiment has been found. The calculated cross sections provide interesting insight into the underlying resonant structure.

Electron impact ionization of plasma important SiClX (X = 1–4) molecules: theoretical cross sections

Electron impact ionization of SiClX (X = 1–4) molecules is less studied but an important process for understanding and modelling the interactions of silicon–chlorine plasmas with different materials. The SiCl3 radical is a major chloro-silicon species involved in the CVD (chemical vapour deposition) of silicon films from SiCl4/Ar microwave plasmas. We report in this paper the total ionization cross sections for electron collisions on these silicon compounds at incident energies from the ionization threshold to 2000 eV. We employ the ‘complex scattering potential-ionization contribution’ method and identify the relative importance of various channels, with ionization included in the cumulative inelastic scattering. New results are also presented on these exotic molecular targets. This work is significant in view of the paucity of theoretical studies on the radicals SiClX (X = 1–3) and on SiCl4.

Absolute angle-differential vibrational excitation cross sections for electron collisions with diacetylene

Absolute vibrational excitation cross sections were measured for diacetylene (1,3-butadiyne). The selectivity of vibrational excitation reveals detailed information about the shape resonances. Excitation of the C{identical_to}C stretch and of double quanta of the C-H bend vibrations reveals a {sup 2}{Pi}{sub u} resonance at 1 eV (autodetachment width {approx}30 meV) and a {sup 2}{Pi}{sub g} resonance at 6.2 eV (autodetachment width 1-2 eV). There is a strong preference for excitation of even quanta of the bending vibration. Excitation of the C-H stretch vibration reveals {sigma}* resonances at 4.3, 6.8, and 9.8 eV, with autodetachment widths of {approx}2 eV. Detailed information about resonances permits conclusions about the mechanism of the dissociative electron attachment.

Time-resolved spectroscopy of the electrode region in a fluorescent lamp1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

In this paper, the ongoing spectroscopic investigations of the plasma inside a fluorescent lamp at Lund Observatory is presented. The intensity of the spectral lines of neutral and singly ionized mercury and krypton in the electrode region in a fluorescent lamp are investigated, both as a function of current through the tube and time resolved during an AC cycle. The results show different dynamics for different spectral lines, which may be due to different population mechanisms and transport phenomena in the discharge. To correctly interpret the data, a model for the electrode region is necessary; however, for this purpose information on processes like electron collision cross-sections, Penning ionization rates, and recombination rates are needed.

Electron-collision cross sections for iodine

We present results from a joint experimental and theoretical study of elastic electron scattering from atomic iodine. The experimental results were obtained by subtracting known cross sections from the measured data obtained with a pyrolyzed mixed beam containing a variety of atomic and molecular species. The calculations were performed using both a fully relativistic Dirac $B$-spline $R$-matrix (close-coupling) method and an optical model potential approach. Given the difficulty of the problem, the agreement between the two sets of theoretical predictions and the experimental data for the angle-differential and the angle-integrated elastic cross sections at 40 eV and 50 eV is satisfactory.

Benchmark calculations of atomic data for plasma and lighting applications

We present the basic ideas behind the recently developed B-spline R-matrix method for the calculation of atomic structure data as well as cross sections for electron and photon collision with atoms and ions. The method is based on the solution of the many-electron close-coupling equations. Employing nonorthogonal sets of atomic orbitals and a flexible B-spline basis makes it possible to generate accurate representations of the target states and the scattering function. Example results from recent applications of the method for benchmark calculations of energy levels, oscillator strengths and low-energy electron scattering from noble gases are presented, as well as a validation of the results through comparison with experimental data from a neon discharge.

CF4기체에서의 전리와 부착계수

In this paper, the electron transport characteristics in CF₄ has been analysed over the E/N range 1~300[Td] by a two-term approximation Boltzmann equation method and by a Monte Carlo simulation. The motion has been calculated to give swarm parameters for the electron drift velocity, longitudinal diffusion coefficient, the ratio of the diffusion coefficient to the mobility, electron ionization and attachment coefficients, effective ionization coefficient, mean energy, collision frequency and the electron energy distribution function.<BR> The electron energy distribution function has been analysed in CF₄ at E/N=5, 10, 100, 200 and 300[Td] for a case of the equilibrium region in the mean electron energy and respective set of electron collision cross sections. The results of Boltzmann equation and Monte Carlo simulation have been compared with experimental data by Y. Nakamura and M. Hayashi.<BR> The swarm parameter from the swarm study are expected to serve as a critical test of current theories of low energy electron scattering by atoms and molecules, in particular, as well as crucial information for quantitative simulations of weakly ionized plasmas.