Absolute Generalized－Oscillator－Strength Measurement of C ls Preionization－Edge Electronic Excitations of C2F6

Absolute generalized oscillator strengths (GOSs) for the C l s preionization-edge transitions at 295.4eV and 297. 7eV in Perfluoroethane have been determined as functions of energy loss and momentum transfer (K) at impact energy of 2.5keV for the first time. The corresponding GOS profiles have been found to have the characteristic dipole-dominated shapes with a strong maximum at K=0. The spectral features can be interpreted in terms of transitions terminating at the σ^*(C-F) molecular orbital.     

Improved Ligand-Field Theoretical Calculations of R-Line Thermal Broadenings of NIgO：Cr^3＋ and MgO：V^2＋

With the values of parameters obtained from improved ligand-field theory, by taking into account all the irreducible representations and their components in EPI as well as all the levels and the admixtures of basic wavefunctions within d^3 electronic configuration, the R-line thermal broadenings （TB） of both MgO：Cr^3＋ and MgO：V^2＋ have microscopic-theoretically been calculated, The results are in very good agreement with the experimental data. It is found that the R-line TB of MgO：Cr^3＋ or MgO：V^2＋ comes from the first-order term of EPI. The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO：Cr^3＋ or MgO：V^2＋.     

Theoretical Calculation of Energy Spectrum of YGG：Cr^3＋ and Thermal Shifts of Its R-Lines

With the strong-field scheme and trigonal bases, the complete d3 energy matrix in a trigonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectrum of YGG：Cr^3＋ at normal pressure and low temperature has been calculated. The g factor of the ground-state has been evaluated in terms of the energy spectrum. At the same time, by using the wavefunctions obtained from diagonalizing the complete d^3 energy matrix and Thermal Shifts theory, we calculate the thermal shifts of the sharp lines of YGG：Cr^3＋ and determine the relevant parameters. The calculated results are all in good agreement with the optical-spectrum and EPR experimental data. It is demonstrated that the obtained wavefunctions and the values of parameters are reasonable.     

Absolute Cross Sections for Near-Threshold Electron-Impact Excitation of the 2s^2S→2p^2P Transition of Li-Like C^3＋, N^4＋, and O^5＋ Ions

Excitation cross sections of 1s^22s ^2S1/2 → 1s^22p^2p1/2,3/2 transition among the fine-structure levels in Li-like C^3＋, N^4＋, and O^5＋ ions are calculated for energies of the near-threshold by using the relativistic distorted-wave program REIE06. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbitals are studied in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. The results of the Li-like C^3＋ ion settle the discrepancy between several previous experiments by using the crossed-beams fluorescence method, in good agreement with the measurements of Savin et al. Moreover, the results in Li-like N^4＋, and O^5＋ ions are compared with the previous experiments, and a good agreement is obtained.     

Theoretical analysis of ion kinetic energies and DLC film deposition by CH4＋ Ar （He） dielectric barrier discharge plasmas

The kinetic energy of ions in dielectric barrier discharge plasmas are analysed theoretically using the model of binary collisions between ions and gas molecules. Langevin equation for ions in other gases, Blanc law for ions in mixed gases, and the two-temperature model for ions at higher reduced field are used to determine the ion mobility. The kinetic energies of ions in CH4 ＋ Ar（He） dielectric barrier discharge plasma at a fixed total gas pressure and various Ar （He） concentrations are calculated. It is found that with increasing Ar （He） concentration in CH4 ＋ Ar （He） from 20% to 83%, the CH4＋ kinetic energy increases from 69.6 （43.9） to 92.1 （128.5）eV, while the Ar＋ （He＋） kinetic energy decreases from 97 （145.2） to 78.8 （75.5）eV. The increase of CH4＋ kinetic energy is responsible for the increase of hardness of diamond-like carbon films deposited by CH4 ＋ Ar （He） dielectric barrier discharge without bias voltage over substrates.     

Theoretical Studies of g Factors and Defect Structures for Cubic, Tetragonal, and Orthorhombic Fe^＋ Centers in Alkali Halides MX （M=Li, Na; X = F, C1）

The EPR 9 factors for cubic, tetragonal and orthorhombic Fe^＋ centers in alkali halides MX （M= Li, Na; X = F, CI） are calculated from second-order perturbation formulas of g factors based on cluster approach for 3d^7 ions in three symmetries. From calculations, the g factors of these Fe^＋ centers in MX crystals are reasonably explained and the defect structural data for the tetragonal and orthorhombic Fe^＋ centers are estimated. The results are discussed.     

Average Energy Loss Measured in Single and Double Electron Capture Collisions of He^2＋ on Ar at Low Velocities ＊

Employing the recoil ion momentum spectroscopy we investigate the collision between He^2＋ and argon atoms. By measuring the recoil longitudinal momentum the energy losses of projectile are deduced for capture reaction channels. It is found that in most cases for single- and double-electron capture, the inner electron in the target atom is removed, the recoil ion is in singly or multiply excited states （hollow ion is formed）, which indicates that electron correlation plays an important role in the process. The captured electrons prefer the ground states of the projectile. It is experimentally demonstrated that the average energy losses are directly related to charge transfer and electronic configuration     

Effect of Reagent Vibrational and Rotational Excitation on the F＋H2 Reaction： Theoretical Study of the Stereodynamics Using Quasi-Classical Trajectory Method

The vector correlations in the reaction F＋H2 （v =0-3, j =0-3）→ HF（v＇, j＇）＋H are investigated using the quasi- classical trajectory method on the Stark-Werner potential energy surface at a collision energy of 1.0eV. The potential distribution P（θr） to angles between k and j＇, the distribution P（Фr） to dihedral angles, denoting k - k＇ - j＇ correlation and the polarization-dependent generalized differential cross sections, are calculated. The effect of reagent vibrational and rotational excitation on the F＋H2 reaction is discussed in detail The results suggest that the different vibrational and rotational quantum states of H2 have different influences on the product polarization.     

Ionization of metastable H(2S) atom by electron and positron impact

Summary Triple differential cross-section (TDCS) of hydrogen atom in its metastable (2S) state is studied theoretically by electron and positron impact for coplanar and asymmetric geometry. The final-state wave function in the present model satisfies the asymptotic boundary condition for asymmetric geometry (i.e. fork ₁≫k ₂). In the absence of experiment, present results are compared with other existing theoretical results. Apart from the double-peaked structure of the TDCS as in ground-state ionization, some interesting secondary structures are found, in conformity with other theories for ionization from 2S state.     

Mutual electron-ion interactions in electron impact ionization of a Ca beam

Summary We evaluate the role of electron-ion mutual interactions as a possible source of systematic errors in an experiment of electron impact ionization and excitation of an effusive Ca beam. By monitoring photons resulting from the impact excitation of a Ca resonant transition, the transmitted electron beam current by a sectored Faraday cup and total ion yields, we extract information about elementary processes responsible for ionization. We show that our diagnosis allows us to monitor the influence of the produced ionization on the elementary processes and on the density profile of the electro beam.     

同轴空心阴极氦等离子体的电子激发温度研究

利用同轴空心阴极放电装置,产生氦低温等离子体。通过对等离子体的发射光谱进行测量和计算,研究放电功率以及氦气压强对等离子体的电子激发温度的影响。结果表明：氦低温等离子体的发射光谱主要由连续谱和原子谱线构成,放电功率和压强对谱线的强度具有明显影响。压强的变化不仅影响电子从电场中获得的能量,还会影响电子与原子的碰撞频率,从而导致电子激发温度随着氦气压强的增大,出现先上升后下降的变化趋势。

     

Ar等离子体射流发射光谱诊断研究

为了深入了解大气压下Ar等离子体射流的产生机理和内部电子的状态,对Ar等离子体射流进行了发射光谱诊断,以玻尔兹曼斜率法对电子激发温度进行测算,利用发射光谱的连续谱绝对强度法测算出电子密度。通过设计一种可调节气压的金属针-环型介质阻挡放电装置,研究了氩气压和放电功率对Ar等离子体射流的电子激发温度和电子密度的影响。结果表明,随着气压从6kPa升高到16kPa,电子激发温度从0.83eV下降到0.68eV,电子密度从4.45×10²²m^-3减小到0.44×10²²m^-3（波长648.06nm）,且随着放电功率从0.1775W增大到1.7926W,电子激发温度从0.82eV升高到5.14eV,电子密度从0.27×10²²m^-3增大到4.61×10²²m^-3,而且电子密度较低时,电子激发温度的变化更明显。由此得出结论,氩气压和放电功率对电子激发温度不仅有直接影响,还有通过电子密度变化导致的间接影响,电子密度较低时,氩气压和放电功率对电子激发温度的影响会相对更大一些。同时,选用两个波长计算的电子密度结果很接近,验证了诊断结果的准确性。     

A Numerical Calculation for Electron Impact Excitation of Copper

The scattering of electrons by atomic copper has been studied using Born approximation and the concept of the generalized oscillator strength (GOS). Differential and total cross-sections for the excitation of the 3d¹⁰ 4p² P state are calculated at incident energies of 100 eV and are compared with other available experimental and theoretical data. The agreement between our calculation for the differential cross-section and the available experimental results is fairly good at the forward angles, while the agreement at large angles is poor. The calculated total cross-sections are compared with the experimental data and those predicted by several theories. It is found that our calculation for the total cross-sections are in a good agreement with the close coupling calculation of Msezane and Henry (1986a, Physical Review A 33, 1631) for incident energies greater than 20 eV. The integrated cross-section measurements of Ismail and Teubner (1995, Journal of Physics B: Atomic, Molecular and Optical Physics 28, 4164) are in good agreement with the present calculation.     

“Electron collisional excitation of argon-like Ni XI using the Breit-Pauli R-matrix method”

In a recent paper, Verma et al. [Eur. Phys. J. D 42, 235 (2007)] have reported results for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the lowest 17 levels of the (1s²2s²2p⁶)3s²3p⁶, 3s²3p⁵3d and 3s3p⁶3d configurations of Ni xi. They adopted the civ3 and R-matrix codes for the generation of wavefunctions and the scattering process, respectively. In this paper, through two independent calculations performed with the fully relativistic darc (along with grasp) and fac codes, we demonstrate that their results are unreliable. New data are presented and their accuracy is assessed.     

Generalized Kolbenstvedt model for electron impact ionization of K-, L- and M-shell atoms

The recently modified Kolbenstvedt (MKLV) model [Eur. Phys. J. D 37, 361 (2006)], developed for electron impact ionization (EII) of the K-shell atomic targets, has been extended to generalize its two parameters in terms of the electronic orbitals nl. The generalized MKLV (GKLV) with two sets of the species independent parameters for the same nl, one set for the ionization of inner orbits and another for the outermost orbit, is found profoundly successful in accounting for the EII cross section data of the K, L and M-shell neutral atoms with atomic numbers Z = 1-92 for the incident energies up to 1000 MeV in a consistent manner.     

Online diagnosis of electron excitation temperature in CH<Subscript>4</Subscript>+H<Subscript>2</Subscript> discharge plasma at atmospheric pressure by optical emission spectra

Methane coupling under low temperature plasmas at atmospheric pressure is a green process by use of renewable sources of energy. In this study, CH₄+H₂ discharge plasma was on-line diagnosed by optical emission spectra so as to characterize the discharge system and to do spade work for the optimization of the technical parameters for future commercial production of methane coupling under plasmas. The study was focused on a calculation method for the online diagnosis of the electron excitation temperature in CH₄+H₂ discharge plasma at atmospheric pressure. The diagnostic method is easy, efficient and fairly precise. A serious error in a literature was corrected during the reasoning of its series of equations formerly used to calculate electron temperatures in plasmas. Supported by the National Natural Science Foundation of China (Grant Nos. 29776037 and 10675028) and the Science and Technology Development Foundation of SINOPEC (Grant No. X500005)     

Empirical model for electron impact ionization cross sections of neutral atoms

A simple empirical formula is proposed for the rapid calculation of electron impact total ionization cross sections both for the open- and closed-shell neutral atoms considered in the range 1≤ Z≤92 and the incident electron energies from threshold to about 10⁴ eV. The results of the present analysis are compared with the available experimental and theoretical data. The proposed model provides a fast method for calculating fairly accurate electron impact total ionization cross sections of atoms. This model may be a prudent choice, for the practitioners in the field of applied sciences e.g. in plasma modeling, due to its simple inherent structure.