Total Cross Sections For Electron-impact Ionization Research Articles

Electron impact partial ionization cross sections: R-carvone, 2-butanol, imidazole, and 2-nitroimidazole.

We calculate electron impact partial and total ionization cross sections of R-carvone (C10H14O), 2-butanol (C4H10O), imidazole (C3H4N2), and 2-nitroimidazole (C3H3N3O2). We have used the Binary Encounter Bethe (BEB) model to obtain total electron impact ionization cross sections (TICSs). The modified BEB method in combination with mass spectrum data of the molecules is used to calculate the partial ionization cross section (PICS) of the cationic fragments dissociating from the parent molecule. Our PICS data for R-carvone and 2-butanol are in good agreement with the experimental data for all the cation fragments along with the TICS data. For imidazole and 2-nitroimidazole, the estimates of the PICS are reported for the first time in the present study. We have found that both the modified BEB method and the mass spectrum dependence method work effectively to estimate PICS if we have information about the appearance energies and relative abundance data of the target under investigation.

Electron impact ionization cross-sections for CH3 and SiH3 radical targets

Single differential cross sections as a function of secondary electron energy at fixed incident electron energies 100 and 200 eV for the targeted molecule CH3 and SiH3 have been evaluated by using a modified Jain-Khare semi-empirical approach. The integral or total electron-impact ionization cross-sections and the averaged energy loss from differential ionization cross-sections are calculated for incident electron energy from the ionization threshold to the 5 keV regimes. The temperature-dependent ionization rate coefficient is also calculated from total ionization cross-sections and Maxwell-Boltzmann electron energy distribution.The calculated values of total ionization cross sections corresponding to (e, 2e) processes for CH3 and SiH3 molecules are in good accord with available theoretical and experimental results.

Electron-Impact Ionization of the Tungsten Ions: W38+ − W45+

In this manuscript, we present our calculations of detailed electron-impact single ionization cross-sections for tungsten ions, spanning charge states W38+− W45+. The level-to-level distorted-wave method implemented in the flexible atomic code (FAC) was used for calculation. Comparison between the present level-to-level distorted wave treatment and previous configuration-averaged calculations has been performed for the W45+ ion, and we explore the possible reason for the difference observed between two calculations. We demonstrate the importance of radiative damping on the total electron-impact ionization cross-section for the W43+ ion. Present calculations provide missing cross-sections for W38+− W45+. The data obtained are expected to be useful for modeling plasmas for fusion applications, especially for the ITER community.

Theoretical calculation of total electron-impact ionization cross section of C6F12O

C6F12O can be used in gas-insulated equipment due to its excellent insulation properties. The purpose of this paper is to calculate the total electron-impact ionization cross section to evaluate the dielectric strength of the molecule using the Deutsch–Märk formula. First, according to the calculation method of quantum chemistry, the structure of the molecule is optimized. Three different methods, such as Mulliken population analysis, C-squared population analysis, and natural atomic orbital (NAO), are used to calculate the molecular orbital components, and then the molecular collision cross section is obtained. The influence of different weighting factors on the calculation results is analyzed. The validity of the proposed method is verified by the calculation results of H2O, C3H6O, and C5F10O. The results show that the calculation value with the NAO method is closer to the experimental results, which provides a reference for the calculation and analysis of the collision cross section of C6F12O. The calculation results in this paper can provide basic data for further calculation of the dielectric strength of C6F12O.

Universal statistical approach to radiative and collisional processes with multielectron ions in plasmas

The universal statistical approach for calculation of radiative and collisional processes with multielectron ions in plasmas is developed. It is based on the atomic structure representation similar to that used in a condensed medium. The distribution of local atomic electron density determines the set of elementary excitations with classical plasma frequency. The statistical method is tested by the calculations of the total electron impact single ionization cross-sections, ionization rates and radiative losses of various ions. In the coronal limit the radiative losses of heavy plasma impurities with any type of multielectron ions are determined by the excitation of collective atomic oscillations due to collisions with plasma electrons. It is shown that for low plasma densities the tungsten ions total radiative loss scatter within universal statistical approach does not exceed similar results of current complex numerical codes in the wide range of plasma temperatures. The general expression for the radiative losses in the case of the intermediate state between limiting cases of coronal and Boltzmann population distributions is derived as well. The total electron impact ionization cross-sections and ionization rates for ions of various charge stages for a wide range of elements from Ar to U are compared with experimental and conventional complex code data showing satisfactory agreement. As the universal statistical method operates in terms of collective excitations, it implicitly includes direct and indirect ionization processes.

Simulation of a QMS Including the Effects of Pressure in the Electron-Impact Ion Source

This paper is concerned with the computer modeling of a quadrupole mass spectrometer (QMS) to include the effect of pressure in the ion source. The paper simulates the spectra over the pressure range from 10-6 to 10-4 mbar. An important contribution is the development of a novel procedure to include pressure dependence of the ion source to allow better prediction of instrument performance. Electron-impact total ionization cross sections in the ionic current expression are calculated using the binary-encounter-Bethe theory for argon gas. The predicted results show good agreement with the experimental results obtained from a commercial QMS used for residual gas analysis.

Absolute Total Electron Impact Ionization Cross-Sections for Many-Atom Organic and Halocarbon Species

The experimental determination of absolute total electron impact ionization cross-sections for polyatomic molecules has traditionally been a difficult task and restricted to a small range of species. This article reviews the performance of three models to estimate the maximum ionization cross-sections of some 65 polyatomic organic and halocarbon species. Cross-sections for all of the species studied have been measured experimentally using the same instrument, providing a complete data set for comparison with the model predictions. The three models studied are the empirical correlation between maximum ionization cross-section and molecular polarizability, the well-known binary encounter Bethe (BEB) model, and the functional group additivity model. The excellent agreement with experiment found for all three models, provided that calculated electronic structure parameters of suitably high quality are used for the first two, allows the prediction of total electron-impact ionization cross-sections to at least 7% precision for similar molecules that have not been experimentally characterized.

Electron impact ionization of atomic target inner-shells

There is a need for reliable theoretical methods to calculate electron-impact total ionization cross sections for the large number of neutral atoms and ions with open shell structures. These cross sections are used in a wide range of scientific and industrial applications, such as astrophysical plasmas, atmospheric science, X-ray lasers, magnetic fusion, radiation physics, semiconductor fabrication, accelerator physics and tumor therapy physics. The binary-encounter-Bethe (BEB) model [1], using an analytic formula that requires only two atomic constants, the binding energy and kinetic energy of the electrons, generates direct ionization cross sections for any neutral atom (or molecule), which are reliable in intensity (15%) and shape from the ionization threshold to a few keV in the incident energy [3], or to thousands keV if we consider its relativistic version(RBEB) [2]. In this work we present K- and L-shell ionization cross sections calculations for heavy atoms.

Electron-impact ionization of B3+ ions

The electron-impact total ionization cross sections for B3+ have been determined both experimentally and theoretically. The experiment was carried out using a parent beam with B3+ ions in a mix of ground 11S and metastable 23S states. The convergent close-coupling (CCC) method has been used to calculate the corresponding cross sections and, by matching with experiment, the ratio of the initial target states in the beam has been determined. Good agreement with experiment across a broad energy range is obtained, particularly when indirect ionization processes are included in the calculations.

Absolute electron impact ionization cross-sections and polarisability volumes for C 2 to C 4 aldehydes, C 4 and C 6 symmetric ethers and C 3 to C 6 ketones

Absolute total electron impact ionization cross-sections from 15 to 285 eV are reported for the C 2 to C 4 aldehydes, the C 2 v symmetric C 4 and C 6 ethers and C 3 to C 6 ketones. The reproducibility of the measured cross-sections over the full energy range is better than ±4%, and absolute cross-sections measured for N 2 and SF 6 as reference species are in excellent agreement with values reported by several other groups claiming accuracies of around ±5%. Monotonic relationships previously shown to exist between maximum ionization cross-section and polarisability volume and between maximum ionization cross-section and the total number of carbon atoms in the skeletal chain are shown to apply to the aldehydes, ethers and ketones reported here. These relationships provide useful means for estimating unknown cross-sections with available literature polarisability volumes in good accord with values estimated from the measured maximum ionization cross-sections. The experimental data were also compared with calculations carried out using the binary encounter Bethe (BEB) method for the calculation of total ionization cross-sections.

Calculation by plane wave Born approximation of the electron-impact ionization of Ne, Ar, Kr and Xe

The relativistic and non-relativistic plane wave Born approximation is used to calculate the total electron impact ionization cross-section of Ne, Ar, Kr and Xe. The wavefunctions of the atom and residual ions are calculated with allowance for relaxation effects. The one-electron wavefunction of the continuous spectrum for the ejected electron is obtained by using the Dirac–Fock method. The role of the relativistic, exchange, orthogonalization and relaxation effects are investigated. Results of calculations are compared to available experimental measurements and theoretical calculations performed by other methods. In particular, we presented the results of our nonrelativistic distorted Born approximation calculations.

Electron impact ionization of M-shell atoms

The modified BELL (MBELL) formula (Haque et al 2006 Phys. Rev. A 73 012708) has been applied to the M-shell ionization of neutral and ionic atoms to deduce the `generalized' parameters of the 3s, 3p and 3d orbits. A single set of parameters for each of these orbits and that previously determined for each of 1s, 2s and 2p orbits can reproduce satisfactorily the features of the total electron impact ionization cross-sections (EIICS) of 21 M-shell targets in the Na, Mg, Al, Si, P, S, Cl, Ar and Ca isoelectronic sequences. The generalized parameters are also found to provide an excellent account of the M-shell EIICS data of Pb, Bi and U atoms at relativistic energies in the range from 20 to 250 MeV.

Electron-impact ionization of Li, Be+, B2+, C3+, N4+ and O5+

A variant of the first Born approximation is used to calculate total electron-impact ionization cross-section. The calculations are performed for the lithium-like targets, Li, …, O5+. Wavefunction of the ejected electrons is presented by distorted wave. High-quality orthogonal initial- and final-state Hartree–Fock Slater orbitals are used to model the target wavefunctions. The wavefunctions of the initial and final states are calculated with allowance for relaxation effect. The one-electron wavefunction of the continuous spectrum for ejected electrons is obtained by using the single-configuration Hartree–Fock method. The present results are compared to available experimental measurements and theoretical calculations with the convergent close-coupling method.

Absolute electron-impact total ionization cross sections of chlorofluoromethanes

An experimental study is reported on the electron-impact total ionization cross sections (TICSs) of CCl4, CCl3F, CCl2F2, and CClF3 molecules. The kinetic energy of the colliding electrons was in the 10-85 eV range. TICSs were obtained as the sum of the partial ionization cross sections of all fragment ions, measured and identified in a linear double focusing time-of-flight mass spectrometer. The resulting TICS profiles--as a function of the electron-impact energy--have been compared both with those computed by ab initio and (semi)empirical methods and with the available experimental data. The computational methods used include the binary-encounter-Bethe (BEB) modified to include atoms with principal quantum numbers n> or =3, the Deutsch and Märk (DM) formalism, and the modified additivity rule (MAR). It is concluded that both modified BEB and DM methods fit the experimental TICS for (CF4), CClF3, CCl2F2, CCl3F, and CCl4 to a high accuracy, in contrast with the poor accord of the MAR method. A discussion on the factors influencing the discrepancies of the fittings is presented.

Total electron-impact ionization cross sections of helium

By accurate measurement of total cross section ratios for electron-impact ionization and photoionization, total electron-impact ionization cross sections of He were determined. Relative standard uncertainties as low as 1.6 to 2% in the electron energy range from 100 to 4000 eV were achieved using published cross section data for photoionization. Results are discussed in terms of theoretical predictions and by comparison with former experimental results. The data are in excellent agreement with the results by Rejoub et al (2002 Phys. Rev. A 65 042713) and represent an accurate and reliable database for testing theoretical models.

Electron impact ionization cross-sections of SF3 and SF5

We report experimental and theoretical studies of the total electron impact ionization cross-sections for the radicals SF3 and SF5. It is shown that for radicals with strongly polar fluoride bonds, the shielding of the attractive dipole interaction potential in the bonding region is important in a proper description of the collision process. The siBED model, which has incorporated the shielding factor, was found to provide cross-sections in agreement with recently re-analyzed experimental data for the species CFx and NFx (x=1–3), whereas the DM model and the BEB model, on the other hand, showed large discrepancies with experiment. These findings also hold for the two free radicals SF3 and SF5 studied here, providing further evidence on the importance of a proper shielding of the dipole potential.

Absolute electron impact ionization cross-sections for CO,CO2, OCSand CS2

Absolute total electron impact ionization cross-sections have been measured for CO,CO2, OCSand CS2 from near threshold to 250 eV. Experimental data are compared with previously reportedmeasurements and with calculations using the additivity method of Margreiter, Deutschand Märk (DM) and the binary encounter Bethe method (BEB). Bond components to thetotal cross-section, previously deduced from systematic studies of perfluorocarbons, mixedhalocarbons, nitriles, chlorocarbons and alcohols, have been shown to reproduce andpredict maximum electron impact cross-sections to a high level of confidence.C = O and C = S bond cross-sections are now reported from the maximum cross-sections forCO2 andCS2, andshown to predict the measured maximum ionization cross-section for OCS to within 4%. The data for OCSand CS2 are shown to be in good accord with the expectations of previously derived relationshipsbetween the maximum ionization cross-section, the molecular volume polarizability and themolecular ion appearance energy (ionization threshold energy).

Total electron-impact ionization cross-sections of CF x and NF x ( x=1–3)

The discrepancy between experimental and theoretical total electron-impact ionization cross-sections of the fluorides CF x and NF x ( x=1–3) is attributed to inadequacies in previous theoretical models. Cross-sections calculated using a recently developed siBED model that takes into account the shielding of the long-range dipole potential in the collision are in agreement with experiment. The present study also re-analyzed the previously reported experimental data to account for incomplete collection of fragment ions and the presence of ion-pair formation channels. For NF 3, our experimental and theoretical cross-sections compare well with the recent data of Haaland et al. in the region below dication formation.

Electron-Impact Total Ionization Cross Sections of Hydrocarbon Ions.

The Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections has been applied to , , , , , and H3O+. The cross sections for the hydrocarbon ions are needed for modeling cool plasmas in fusion devices. No experimental data are available for direct comparison. Molecular constants to generate total ionization cross sections at arbitrary incident electron energies using the BEB formula are presented. A recent experimental result on the ionization of H3O+ is found to be almost 1/20 of the present theory at the cross section peak.

Approximate inelastic scattering cross sections of electrons

The approximate expressions for the differential inelastic scattering cross sections of electrons in a medium are proposed from distant and close interactions using generalized oscillator strength. The approximate total inelastic scattering cross section of electrons in a medium is calculated by using the presented expressions for distant and close interactions. For several media, the calculated K- and L-shell electron-impact ionization cross sections, total electron-impact ionization cross sections and inelastic mean free paths and collision stopping powers of electrons are compared to other theoretical and experimental values available from the literature.