Electron-impact ionization cross-sections and ionization rate coefficients for atoms and ions from hydrogen to calcium

Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for all ionization stages from hydrogen to calcium (Z=20). Ionization rate coefficients are given for these species on the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account.     

Electron-impact ionization cross-sections and ionization rate coefficients for atoms and ions from scandium to zinc

Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for nearly all ionization stages from scandium (Z=21) to zinc (Z=30). For these species ionization rate coefficients are given under the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account.     

Decay properties of neutron-deficient isotopes of elements from Z = 101 to Z = 108

In a series of experiments performed at the velocity filter SHIP, new or improved decay data of neutron-deficient isotopes of elements from mendelevium (Z = 101) to hassium (Z = 108) were obtained. In particular, evidence for -decay or electron capture from isomeric states in ²⁶⁵Hs and ²⁵⁸Db was found.     

Modified Kolbensvedt model for the electron impact K-shell ionization cross-sections of atoms and ions

A modification of the Kolbensvedt model, MKLV, in terms of ionic, correlation (between the incident and target electrons) and relativistic corrections, is proposed to calculate the K-shell electron impact ionization cross-sections of neutral and ionic targets. The modified model, with a single set of parameters, is found to reproduce satisfactorily the experimental data for the neutral H, Al, Ar, Mn, Ge, Mo, Ag, Sn, Au, Bi and U and ionic Li⁺, B⁴⁺ and O⁷⁺ targets better than the existing empirical models from threshold energies to as high as 10⁴ MeV. For the Ag target, the calculations from MKLV follow closely the results of Scofield, and for Au, those of Scofield, and Ndefru and Malik, both done in the relativistic Born approximation with the M?ller interaction, at energies higher than the peak region.     

Electron-impact ionization and excitation of helium to the n=1-4 ionic states

We present high-precision (e,2e) measurements and calculations for the e-He four-body Coulomb breakup problem. Cross-section ratios for ionization and excitation of the first three excited states of He+ relative to the ground state have been measured for incident energies between 112 and 319 eV. Comparing the data with predictions from a state-of-the-art hybrid distorted-wave+convergent R matrix with pseudostates (close coupling) approach shows that treating the projectile-target interaction at least to second order is crucial to obtain reasonable agreement between theory and experiment. Nevertheless, our benchmark studies reveal significant theoretical problems for the symmetric energy-sharing cases, thus indicating the need for further improvement.     

Calculation of triple differential cross-sections ofK-shell ionization of medium-heavy atoms by electrons for symmetric geometry

Triple differential cross-section forK-shell ionization of medium-heavy atoms by relativistic electrons has been calculated for coplanar symmetric geometry. In this calculation the final state is described by a non-relativistic wave function of Das and Seal [Phys. Rev. A47 (1993) 2978] multiplied with suitable spinors. Results of the present calculation are compared with the available experimental data and with other theoretical calculations.     

Electron-impact ionization cross section calculations for lithium-like ions

The electron-impact ionization of lithium-like ions C³⁺,N⁴⁺,O⁵⁺,Ne⁷⁺,and Fe2³⁺is studied using a combination of two-potential distorted-wave and R-matrix methods with a relativistic correction.Total cross sections are computed for incident energies from 1 to 10 times of ionization energy and better agreements with the experimental results are obtained in comparison with the theoretical data available.It is found that the indirect ionization processes become significant for the incident energy larger than about four times of the ionization energy.Contributions from the exchange effects along the isoelectronic sequence are also discussed and found to be important.The present method can be used to obtain systematic ionization cross sections for highly charged ions across a wide incident energy range.     

Triple differential cross-sections for the ionization of metastable 2P-state hydrogen atoms by electrons with exchange effects

In this paper, triple differential cross-sections for the ionization of metastable 2P-state hydrogen atoms by 250 eV electron energy with exchange effects for various kinematic conditions are calculated. Multiple scattering theory proposed by Das and Seal in Phys. Rev. A 47, 2978 (1993) is utilized here. The computational results provide significant peak features that show good qualitative agreement with the hydrogenic ground-state experimental data and theoretical results and the present first Born results. In addition, physical origin of the peaks of the cross-section curves is investigated.     

Electron-impact ionization cross sections and rates for ions of argon

A distorted-wave Born exchange (DWBE) approximation including relativistic correction is used to calculate the electron-impact ionization cross sections and rate coefficients for the highly charged ions Ar⁷⁺,…,Ar¹⁷⁺. The comparison of the calculated results with the experimental data and other theoretical calculations shows that the DWBE method is valid for these ions of argon. The calculated results for direct ionization cross sections and excitation autoionization were fitted by empirical formulas to meet the requirements of applications. A set of improved empirical formulas are used for the fast and accurate calculations of rate coefficients from the fit parameters of cross sections.     

Total electron ionization cross-sections for molecules of astrochemical interest

ABSTRACT

We describe a newly upgraded instrument for measuring absolute total electron ionization cross-sections over the energy range from 0 to 300?eV, and present cross-sections for nine previously unstudied molecules, as well as several small molecules for which comparison data is available. The measured cross-sections are compared with the predictions of the BEB model, and show reasonable agreement with the model, albeit peaking at higher electron energies than predicted by the model. We show that the maxima in the cross-sections follow an additivity model, such that the molecular cross-sections can be expressed as a sum over contributions from the constituent atoms. These contributions have been determined from a global fit to the data for all molecules studied, and allow maximum cross-sections to be predicted for molecules that have not been studied to date. We demonstrate the expected correlation between the maximum ionization cross-section and the molecular polarisability, and show that the atomic contributions to the cross-section show a similar dependence on the atomic polarisability. The observed correlation can be used as an alternative method for predicting unknown maximum cross-sections.     

Ellipticity-dependent ionization yield for noble atoms

The photoionization in the frame of the Ammosov–Delone–Krainov theory has been theoretically examined for noble gases, argon, krypton, and xenon, in an elliptically polarized laser field. We consider the intermediate range of the Keldysh parameter, γ～1, and analyze the influence of shifted ionization potential and temporal profile to eliminate disagreement between theoretical and experimental findings. By including these effects in the ionization rates, we solve rate equations in order to determine an expression for the ionization yield. The use of modified ionization potential shows that the ionization yields will actually decrease below the values predicted by original(uncorrected) formulas. This paper will discuss the causes of this discrepancy.     

Total and transport elastic cross-sections for excited muonic and pionic hydrogen atoms

The results of an experiment on muon catalyzed dd-fussion in HD gas are presented. The experiment was performed at the muon beam of PSI using a high-pressure ionization chamber filled with pure HD-gas of low D₂ concentration on the level 1%, at temperatures 50, 150 and 300 K. The non-resonant character of ddμ-molecule formation on HD molecules was confirmed by measuring the ratio of yields of the two ddμ-fusion channels, R=Y(³He,n)/Y(³H,p), which proved to be close to unity. The ddμ formation rate was found to vary from λ_ddμ-HD=0.05· 10⁶ s^-1 at T=50 K to λ_ddμ-HD=0.12· 10⁶ s^-1 at T=300 K, in agreement with the theoretical prediction. A prominent peak at t<60 ns was observed in the time spectrum of fusion neutrons indicating a resonant contribution of ddμ formation from epithermal dμ atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Statistic approach to multiphoton,multielectron ionization of atoms

The density of states and the excitation temperature of an atom are found. To describe the ionization process, a diffusion equation with ejection is proposed. It is shown that the possibility of multielectron ionization is determined by the competition of the heating of an atom by an external field and evaporative ionization. A numerical calculation is made of the ionization of xenon atoms and a comparison with experimental results is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 44–48, April, 1988.     

Measurement of ionization cross-sections and backscattering factors for use in quantitative AES

For the extraction of quantitative information from Auger electron spectra two parameters (apart from a number of instrumental parameters) are of utmost importance: the ionization cross-section and the backscattering factor. The determination of these two parameters is discussed. Ionization cross-section values for L- and M-shells have been determined based on existing values for K-shells from the literature. The backscattering factor for Si is calculated as a function of energy of the primary electrons and compared with absolute measurements of this factor using an adsorbed monolayer of sulfur or oxygen on a Si (100) surface.     

Optimized effective potential energies and ionization potentials for the atoms Li to Ra

A systematic application of the optimized effective potential equations for atoms in both the non-relativistic and relativistic cases is carried out. The ground state energy and the ionization potential of the atoms Li through to Ra is obtained. In the relativistic case, a trial wave function including all of the jj configurations that contribute to the ground state term within the electronic configuration are included. The results are compared with the corresponding Hartree-Fock and Dirac-Hartree-Fock values.