Electron Collision Cross Sections Research Articles

Theoretical study of the low-energy electron-collision cross sections of isomers HOOCl, HOClO and HClOO in gas phase

Cross sections for the elastic electron scattering by HOOCl, HOClO and HClOO isomers are calculated using the R-matrix method. A systematic study considering basis set, polarisation and the Born closure technique is performed. Low-energy resonances are found for both HOOCl and HOClO, near 1.7 and 1.2 eV respectively, but not for HClOO. The lowest-energy resonance for HClOO is observed at 4.5 eV. Basis sets and polarisation effects on the differential cross sections are found to be important for scattering energies below 5 eV for HOOCl and HOClO due to the presence of these resonances. The dependence of the molecular dipole moment on target basis set used affects the integral cross sections (ICS) results. The ICS for HOClO is larger than other two isomers due to its larger dipole moment, around 3.2 D, while the ICS for HOOCl and HClOO have similar magnitude as both their dipole moments are near 1.9 D. Estimated dissociative electron attachment (DEA) cross sections suggest that HOOCl and HOClO will undergo DEA with low-energy electrons but that HClOO requires higher-energy electrons to undergo DEA.

Dissociative reactions induced by electron impact and electron transport in TEOS vapor

Reactions for dissociative ionization and neutral dissociation collisions between an electron and a tetraethoxysilane [Si(OC2H5)4, TEOS] molecule are reported, and neutral dissociation cross sections are calculated by applying the classical Rice–Ramsperger–Kassel theory. Detailed electron collision cross section set of TEOS vapor, including 18 neutral dissociation cross sections and 20 ionization cross sections, is constructed. Electron transport coefficients, such as the mean-arrival-time drift velocity, bulk drift velocity, longitudinal bulk diffusion coefficient, and ionization coefficient, and rate coefficients for both elastic and inelastic collisions in TEOS vapor are calculated from the present cross section set using a Monte Carlo method. The validity of the present cross section set is demonstrated by comparing the calculated electron transport coefficients with measured data. Furthermore, fragmentation of TEOS molecules by electron impact is simulated, and then the number of fragments produced in the simulation is compared with the measured mass spectra.

Set of the Electron Collision Cross Sections for Methane Molecule

This paper represents a contribution toward finding a complete set of electron collision cross sections for the methane molecule by revising all of the collision cross sections and adding the partial collision cross sections data relating to dissociation by electron impact. For the latter, there are no available measurements data for each channel of dissociation and no validated recommended data for use in the modeling, although these data are very important in order to determine different species in a methane plasma. The rate coefficients of the partial dissociative collisions into neutrals and the partial ionization collisions are also calculated, and when fitted, these can be used as input for fluid models. This paper is concluded by the validation of our set of data through a comparison between the transport coefficients calculated by using our data and the measurements of the transport coefficients that already exist in the literature.

Electron transport in nonideal and degenerate plasmas

In this article, various methods of calculation for the Coulomb logarithm in the kinetic theory of electron transfer are considered. It is assumed that the interaction of electrons with ions is described by the Debye potential with a screening constant, which is determined either with or without the contribution of the ionic component. In order to take into account ion–ion correlations, the Ornstein–Zernike integral equation in the hypernetted chain approximation is solved numerically. The behavior of the collision cross section of electrons with ions has been studied in detail on the basis of the phase shift method.

Electron Collision Cross Sections for the TRIES Molecule and Electron Transport Coefficients in TRIES-Ar and TRIES-O2 Mixtures

A reliable set of low-energy electron collision cross sections for the triethoxysilane (TRIES) molecule was derived based on the measured electron transport coefficients for a pure TRIES molecule by using an electron swarm method and a two-term approximation of the Boltzmann equation. The electron transport coefficients calculated using the derived set are in good agreement with experimental value 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 TRIES molecule, therefore, is the most reliable so far for plasma discharges and for materials processing using the TRIES molecule. Moreover, the electron transport coefficients for the TRIES-Ar and the TRIES-O2 mixtures were also calculated and analyzed over a wide range of E/N for the first time.

Cross sections for electron collision with pyridine [C5H5N] molecule

ABSTRACTThe absolute grand -total cross section (TCS) for electron scattering from pyridine, C5H5N, molecules has been measured at impact energies from 0.6 to 300 eV in the linear electron-transmission experiment. The obtained TCS energy dependence appears to be typical for targets of high electric-dipole moment; the cross section generally decreases with rising energy, except for the 3–20 eV range, where a broad enhancement peaked near 8.5 eV is clearly visible. Below 10 eV, some weak structures which can be attributed to resonant scattering processes are also discernible. The present TCS energy dependence is compared with TCS experimental data reported very recently. Comparison with TCS for benzene is also made to search how the replacement of the CH group in the benzene ring with the nitrogen atom influences the electron-scattering process. In addition, for pyridine and its halogenated derivatives: 2-chloropyridine [2-CHClN] and 2-bromopyridine [2-CHBrN], integral elastic (ECS) and ionisation (ICS) cross sections have been calculated at intermediate and high electron-impact energies within semiempirical approaches. For pyridine the sum of ECS and ICS is in reasonable agreement with the measured TCS above 40 eV.

Measurement of electron swarm coefficients in chlorine and its mixtures with nitrogen

We have measured the electron drift velocity, density-normalized longitudinal diffusion and effective ionization coefficients for electrons in Cl2 and Cl2–N2 mixtures over the combined E/N range from 3 to 450 Td, using a pulsed Townsend apparatus especially designed to withstand the action of corrosive gases. Our measurements for the electron drift velocity and the effective ionization coefficient are compared with the only two previous measurements available, one of them indirect. In view of the present incompleteness and uncertainty in the electron collision cross section set for Cl2, Cl2–N2 mixtures with Cl2 contents from 1% to 80% have been measured in the aim of shedding more light into the completeness and reliability of the cross section set by testing the cross sections derived for pure Cl2 with those of the Cl2–N2 mixture for which the cross sections for N2 are well known.

Low-energy electron elastic scattering from ethylene oxide and thiirane

We present elastic integral cross sections for electron collisions with ethylene oxide and thiirane. The calculations were performed with R-matrix method in the static-exchange and static exchange polarization approximations for electron energies ranging from 0.01 to 15 eV. We found two shape resonances in the 2B1 and 2B2 symmetry in each molecule. We also detected one shape resonance in the 2A1 symmetry for thiirane. The positions of the resonances agree well with available results. We shed some light on the nature of the resonances of these two compounds together with molecular orbital calculations. The similarities and differences among the resonances are discussed.

Absolute cross section measurements for the scattering of low- and intermediate-energy electrons from PF3. I. Elastic scattering.

We report absolute elastic differential cross sections (DCSs) for electron collisions with phosphorus trifluoride, PF3, molecules (e- + PF3) in the impact energy range of 2.0-200 eV and over a scattering angle range of 10°-150°. Measured angular distributions of scattered electron intensities were normalized by reference to the elastic DCSs of He. Corresponding integral and momentum-transfer cross sections were derived by extrapolating the angular range from 0° to 180° with the help of a modified phase-shift analysis. In addition, due to the large dipole moment of the considered molecule, the dipole-Born correction for the forward scattering angles has also been applied. As a part of this study, independent atom model calculations in combination with screening corrected additivity rule were also performed for elastic and inelastic (electronic excitation plus ionization) scattering using a complex optical potential method. Rotational excitation cross sections have been estimated with a dipole-Born approximation procedure. Vibrational excitations are not considered in this calculation. Theoretical data, at the differential and integral levels, were found to reasonably agree with the present experimental results. Furthermore, we explore the systematics of the elastic DCSs for the four-atomic trifluoride molecules of XF3 (X = B, N, and P) and central P-atom in PF3, showing that, owing to the comparatively small effect of the F-atoms, the present angular distributions of elastic DCSs are essentially dominated by the characteristic of the central P-atom at lower impact energies. Finally, these quantitative results for e- - PF3 collisions were compiled together with the previous data available in the literature in order to obtain a cross section dataset for modeling purposes. To comprehensively describe such a considerable amount of data, we proceed by first discussing, in this paper, the vibrationally elastic scattering processes whereas vibrational and electronic excitation shall be the subject of our following paper devoted to inelastic collisions.

Cross Sections for Electron Collisions with Ammonia

Cross-sectional data are surveyed for electron collisions with ammonia. Collision processes considered are total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational, and electronic states, ionization, and dissociative electron attachment. After a review of the literature (up to March 2017), recommended values of the cross section are determined, as far as possible.

Cross Sections for Electron Collisions with NF3

Cross section data are compiled from the literature for electron collisions with nitrogen trifluoride (NF3) molecules. Cross sections are collected and reviewed for total scattering, elastic scattering, momentum transfer, excitations of rotational and vibrational states, dissociation, ionization, and dissociative attachment. For each of these processes, the recommended values of the cross sections are presented. The literature has been surveyed until end of 2016.

Cross-sections for electron-scattering from 2-methyl-1-buten-3-yne, C5H6, molecules

Cross-sections for electron collisions with the 2-methyl-1-buten-3-yne [H2CC(CH3)CCH] molecule were measured and calculated. Absolute grand-total electron-scattering cross-section (TCS) was taken at impact energies from 0.6 to 300eV in the linear electron-transmission experiment. The TCS energy dependence for the electron–C5H6 collision has two prominent enhancements separated with a deep minimum located near 1.8eV. In addition, in the low-energy TCS function two noteworthy features occur: (i) near 1eV, a change in a slope on rapidly declining side of the TCS curve; (ii) between 2 and 5eV, a distinct hump superimposed on the opposite, rising part of the curve. To search for the origin of these features in the TCS curve for C5H6, the comparison was made with results of the electron-scattering studies for selected hydrocarbon molecules. These features were attributed to the formation of short-living negative ions (resonant states). Elastic (ECS) and ionization (ICS) cross-sections for C5H6 and C4H2 (1,3-butadiyne) were computed up to 3keV by means of the additivity rule (AR) approximation and the binary-encounter-Bethe (BEB) approach, respectively. For the C5H6 molecule, the sum ECS+ICS is in good agreement with the experimental TCS for energies above about 40eV.

Electron scattering by the hydrocarbons C4H6,C5H8 , and C6H10

We report calculated elastic integral and differential cross sections for electron collisions with the hydrocarbons 1,3-butadiene (${\mathrm{C}}_{4}{\mathrm{H}}_{6}$), 2-methyl-1,3-butadiene (${\mathrm{C}}_{5}{\mathrm{H}}_{8}$), and 2,3-dimethyl-1,3-butadiene (${\mathrm{C}}_{6}{\mathrm{H}}_{10}$) for impact energies up to 15 eV. Our calculations were performed with the Schwinger Multichannel Method with pseudopotentials, in the static-exchange and static-exchange plus polarization approximations. These molecules differ for the presence of one methyl group, in the case of ${\mathrm{C}}_{5}{\mathrm{H}}_{8}$, and two methyl groups, in the case of ${\mathrm{C}}_{6}{\mathrm{H}}_{10}$ in substitution of one and two hydrogen atoms in ${\mathrm{C}}_{4}{\mathrm{H}}_{6}$, respectively (methylation effect). For the polar molecule 2-methyl-1,3-butadiene, we included the Born closure procedure in order to account for the long-range potential. We found two ${\ensuremath{\pi}}^{*}$ shape resonances in the integral cross section of each one of the molecules studied. The present results are also compared with the experimental values for the resonances positions and with total cross sections available in the literature. In particular, we show that the minimum in the total cross section of ${\mathrm{C}}_{5}{\mathrm{H}}_{8}$ located at around 1.6 eV and assigned by the authors as a Ramsauer-Townsend minimum is, actually, a valley between the two ${\ensuremath{\pi}}^{*}$ shape resonances. Also for the ${\mathrm{C}}_{5}{\mathrm{H}}_{8}$ molecule, the enhancement in the total cross section below 1.6 eV is the tail of the low-lying shape resonance and not an effect due to its permanent dipole moment, as suggested by the authors. We discuss the influence of the methylation effect in the shape and magnitude of the elastic cross sections and also in the location of the ${\ensuremath{\pi}}^{*}$ shape resonances of these hydrocarbons.

Averaged electron collision cross sections for thermal mixtures of β-alanine conformers in the gas phase

A theoretical study of elastic electron scattering by gas-phase amino acid molecule β-alanine (NH2–CH2–CH2–COOH) is presented. R-matrix calculations are performed for each of the ten lowest-lying, thermally-accessible conformers of β-alanine. Eigenphase sums, resonance features, differential and integral cross sections are computed for each conformer. The positions of the low-energy shape resonance associated with the unoccupied orbital of the −COOH group are found to vary from 2.5 to 3.3 eV and the resonance widths from 0.2 to 0.5 eV depending on the conformation. The temperature-dependent population ratios are derived, based on temperature-corrected Gibbs free energies. Averaged cross sections for thermal mixtures of the 10 conformers are presented. A comparison with previous results for the α-alanine isomer is also presented.

Electron collisions with F2CO molecules

In this paper we present elastic differential, integral, and momentum-transfer cross sections for electron collisions with carbonyl fluoride $({\mathrm{F}}_{2}\mathrm{CO})$ molecules for the incident electron's energy from 0.5 eV to 20 eV. The Schwinger multichannel method with pseudopotentials was employed to obtain the cross sections in the static-exchange and static-exchange plus polarization approximations. The present results were compared with the available data in the literature, in particular, with the results of Kaur, Mason, and Antony [Phys. Rev. A 92, 052702 (2015)] for the differential, total, and momentum-transfer cross sections. We have found a ${\ensuremath{\pi}}^{*}$ shape resonance centered at 2.6 eV in the ${B}_{1}$ symmetry and other resonance, in the ${B}_{2}$ symmetry, located at around 9.7 eV. A systematic study of the inclusion of polarization effects was performed in order to have a well balanced description of this negative-ion transient state. The effects of the long-range electric dipole potential were included by the Born closure scheme. Electronic structure calculations were also performed to help in the interpretation of the scattering results, and associate the transient states to the unoccupied orbitals.

Cross sections for electron collision with fluoroacetylene: A comparative study with acetylene and difluoroacetylene along with fluorination

Low energy electron impact cross sections of fluoroacetylene (HCCF) are investigated using the R-matrix method. The best target model, which gave good target properties in comparison with literature values, is used for the final scattering calculation. The fluorination effect on the various elastic, momentum transfer, differential, excitation and ionization cross section is studied by comparing the present results with the recent theoretical results of difluoroacetylene (FCCF) and acetylene (HCCH). This is the first reported detailed investigation of cross sections for HCCF along with the fluorination effect.

Low-energy and very-low energy total cross sections for electron collisions with N2

Absolute grand total cross sections for electron scattering from N2 are obtained in the energy range from 20 eV down to 5 meV with very narrow electron energy width of 9 meV using the threshold-photoelectron source. Total cross sections obtained in the present study are compared with the previous experimentally obtained results. At the very-low energy region below 50 meV, the present total cross sections are somewhat smaller than those reported by the Aarhus group [S.V. Hoffmann et al., Rev. Sci. Instrum. 73, 4157 (2002)], which has been the only experimental work that provided the total cross sections in the very-low energy region. The energy positions of the peaks in the total cross sections due to the 2 Π g shape resonance are obtained with higher accuracy, due to the improved uncertainty of the energy position in the present measurement compared to the previous works. The resonance structure in the total cross sections due to the Feshbach resonances of N2 at around 11.5 eV are also observed. Analysis of the resonant structure was carried out in order to determine the values of resonance width of Feshbach resonances of N2.

Calculated cross sections for electron collisions with NF3, NF2 and NF with applications to remote plasma sources

Electron impact cross sections sets are constructed for the nitrogen trifluoride, nitrogen difluoride and nitrogen monofluoride molecules. These cross sections are based on ab initio R-matrix calculations augmented by other procedures. Cross sections are presented for elastic collisions, momentum transfer, dissociative electron attachment, electron impact dissociation, ionisation and dissociative ionisation. For NF process occurring via the metastable a and b states are also considered. A semi-empirical method of estimating the products of electron impact ionisation is proposed and tested for ammonia. The cross sections are extended to high energy where appropriate. The cross section set constructed is tested in a global model simulation of a low pressure, inductively coupled plasma based on a Ar/NF3/O2 initial gas mixture.

Electron transport parameters in CO2: scanning drift tube measurements and kinetic computations

This work presents the transport coefficients of electrons (bulk drift velocity, longitudinal diffusion coefficient, and effective ionization frequency) in CO2 measured under time-of-flight conditions over a wide range of the reduced electric field, in a scanning drift tube apparatus. The data obtained in the experiments are also applied to determine the effective steady-state Townsend ionization coefficient. These parameters are compared to the results of previous experimental studies, as well as to the results of various kinetic computations: solutions of the electron Boltzmann equation under different approximations (multiterm and density gradient expansions) and Monte Carlo simulations. The experimental data extend the range of E/N compared with previous measurements and are consistent with most of the transport parameters obtained in these earlier studies. The computational results point out the range of applicability of the respective approaches to determine the different measured transport properties of electrons in CO2. They also demonstrate the need for further improvement of the electron collision cross section data for CO2 taking into account the present experimental data.

Influence of the gassing materials on the dielectric properties of air

Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and validated. Then the species compositions of the air–organic vapor mixtures were calculated based on the Gibbs free energy minimization. Finally, the Townsend ionization coefficient, the Townsend electron attachment coefficient and the critical reduced electric field strength were derived from the calculated electron energy distribution function by solving the Boltzmann transport equation. The calculation results indicated that H2O with large attachment cross sections has a great impact on the critical reduced electric field strength of the air–organic vapor mixtures. On the other hand, the vaporization of gassing materials can help to increase the dielectric properties of air circuit breakers to some degree.