Total dielectronic recombination rate coefficient for Co-like tungsten

Ab initio calculation of the total dielectronic recombination (DR) rate coefficient from the ground state 3s²3p⁶3d⁹(J=5/2) of Co-like tungsten is performed employing the relativistic distorted-wave approximation with configuration-interaction. The DR contributions mainly come from complex series 3d⁸4ln′l′. The complex series 3p⁵3d¹⁰n′l′, 3p⁵3d⁹4ln′l′ and 3d⁸5ln′l′ also contribute significantly to the total DR rates at relatively high electron temperatures. The l′ and n′ dependences of the partial rate coefficient are investigated. The inclusion of decays into autoionizing levels followed by radiative cascades (DAC) enlarges the total DR rate coefficients by a factor of about 10%. The level-by-level extrapolation method is developed to include DAC effects. The total DR rate coefficients are fitted to an empirical formula. It is shown that at temperatures above 2.5 keV the Burgess-Merts (BM) semiempirical formula can provide DR results with an accuracy of about 15%, whereas at electron temperatures below 100 eV it underestimates the DR rate coefficients by up to a few orders of magnitude and its temperature dependence is completely inadequate. The comparison of the results for Ni-like and Co-like tungsten shows that these two sets of DR rate coefficients are very close in magnitude at relatively high electron temperatures.     

类氖等电子系列离子基态的双电子复合速率系数研究

使用全相对论组态相互作用方法, 能级-能级细致计算了0.1 E_I ≤ kT_e≤ 10 E_I (E_I是类钠离子基态的第一电离能) 温度范围内类氖离子基态双电子复合(DR)速率系数, 双激发自电离能级考虑了(2s2p)⁷3ln'l', (2s2p)⁷4l4l' 以及(2s2p)⁷4l5l'组态. 对于(2s2p)⁷3ln'l'双激发自电离组态, 轨道角量子数l' >8 的(2s2p)⁷3ln'l'双激发自电离态对双电子复合速率系数的贡献可以忽略不计; (2s2p)⁷3ln'l'双激发自电离组态的高里德堡态对双电子复合速率系数的贡献满足 n'^-3组态-组态外推法, 并且核电荷数越大, 趋于n'^-3标度的n'值越小; 对细致能级计算得到的类氖离子基态的总DR速率系数进行了拟合, 得到类氖离子基态的总DR速率系数随核电荷数 Z和电子温度变化的经验公式, 该拟合公式与细致计算结果的偏差在2%以内, 能较准确的计算任意核电荷数Z的类氖离子在0.1E_I ≤ kT_e ≤ 10E_I电子温度范围的DR速率系数. Burgess-Merts(BM)近似公式不适用于估算低温(kT_e<0.3 E_I)类氖离子的DR速率系数, 在高温(kT_e>2E_I)时, 类氖离子的DR速率系数可以用BM近似公式表示.     

Energy levels and probabilities of radiative transitions in the Kr IX ion

The energy levels of the 3d ⁹4l (l = 1–3) and 3p ⁵3d ¹⁰4l (l = 0, 1) configurations in the Kr IX ion and the probabilities of radiative transitions to the ground state from these excited states have been calculated within the relativistic perturbation theory using a zero-approximation model potential. The results are shown to be stable within this approximation. The well-known problem of anomalously low accuracy of the calculations of some higher lying singlet levels is considered.     

DIELECTRONIC RECOMBINATION OF Co-LIKE Ag AND Ta IONS

Ab initio calculations of the rate coefficients for dielectronic recombination (DR) of Co-like Ag and Ta ions are performed based on Cowan's quasi-relativistic multi-configuration Hartree－Fock code. Co-like (3s ²3p⁶3d¹⁰)^-1 configurations and Ni-like (3s²3p⁶3d¹⁰)^-24l4l' autoionization configurations are included in the present calculation. Because of the extensive distribution of autoionization state energy levels, the DR rate coefficients cannot be reproduced or interpolated by a simple analytical formula, such as the Burgess－Merts formula, or the Hagelstein approximation. We propose to use multi-set Hagelstein parameters, which is convenient in practice and can reproduce well the ab initio calculated DR rate coefficients.     

The effect of configuration complex on dielectronic recombination process in highly ionized plasmas

This paper analyses the effect of configuration complex on dielectronic recombination （DR） process in highly ionized plasmas （Xe^26＋, Dy^38＋, W^46＋） by using the multiconfiguration relativistic Hartree-Fock method. Resonant and nonresonant radiative stabilizing transitions and decays to autoionizing levels followed by radiative cascades are included. Collisional transitions following electron capture are neglected. The remarkable difference between the isoelectronic trend of the rate coefficients for DR through 3d^94l4l′ and through 3d^94l5l′ is emphasized. The trend of DR through 3d^94l4l′ shows irregularities at relatively low temperature due to the progressive closing of DR channels as atomic number Z increases.     

Characteristics of the decay of quartet states in the isoelectronic sequence Li-Ne+7

The oscillator strengths, probabilities, and intensities of radiative transitions and radiative lifetimes are calculated within the framework of the quartet term structure 1s2snl ⁴L, 1s2snl'⁴ (l = 0, 1, 2, 3;l' = 0, 1, 2;n5)Lin the isoelectronic sequence Li-Ne⁺⁷. The probabilities for Coulomb autoionization into the quartet continuum are calculated. The general regularities in the quartet spectra in the isoelectronic series and the z-dependence of some optical characteristics are studied. The predominant decay channels of quartet terms are investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 10–14, October, 1988.     

Autoionizing and highly excited states in the spectrum of triply ionized tin Sn IV

Transitions from autoionizing states in the spectrum of Sn IV in the range 200–630 Å, occurring due to the excitation of electrons from the inner 4d ¹⁰ shell, are investigated with high resolution. The transitions from the 4d ⁹5p ², 4d ⁹5s6p, and 4d ⁹5snf (up to n = 9) configurations are identified and their autoionization widths are measured. Transitions from the highly excited 4d ¹⁰ ns (n = 8–10), 4d ¹⁰6p, and 4d ¹⁰7d configurations are also revealed and the ionization potential of Sn IV is refined. The data obtained are compared with the results of calculations by the Hartree-Fock and semiempirical methods.     

类铷W37+离子双电子复合速率系数的理论研究

 利用全相对论组态相互作用理论方法,研究了类铷W³⁷⁺离子从基组态3s²3p⁶3d¹⁰4s²4p⁶4d经过双激发态(3s²3p⁶3d¹⁰4s²4p⁶4d)^-1nln′l′(n,n′=4,5)的双电子复合过程,得到了该离子在温度为1~5×10⁴ eV范围内的总双电子复合速率系数。分析比较了不同电子激发的双电子复合速率系数,结果表明:4p电子激发的双电子复合速率系数在低温时给出了主要贡献,而3d的贡献在高温时突出。由于强组态相互作用,两电子一光子跃迁对双电子复合速率系数的贡献不可忽略,其中辐射跃迁4p⁵4d5d5f-4p⁶4f5d的贡献是双激发态4p⁵4d5d5f总的双电子复合速率系数的5%。对双电子复合、辐射复合以及三体复合速率系数的比较表明,在所研究的温度范围内双电子复合速率系数最大。     

Electronic structure and properties of strontium ferrite Sr3Fe2O6

The electronic structure of strontium ferrite Sr₃Fe₂O₆ was calculated using the tight-binding linear muffin-tin orbital method (TB LMTO) in the local spin density approximation of density functional theory with Coulomb correlations correction (LSDA+U). The semiconducting character of the spectrum with charge transfer energy gap of 1.82 eV was obtained in reasonably good agreement with experimental data. The iron ions are found to be in the high spin state. The calculated value of the local spin magnetic moment of Fe³⁺ ion is 3.94 μ_B which is not typical for trivalent iron ion in the high spin state. It is shown that the strong hybridization between Fe3d and O2p orbitals favors the d⁶ L configuration of Fe³⁺ ion, where L is a hole in the oxygen p shell. The mechanism of oxygen transport in ferrite is discussed basing on the total energy calculations of the different spatial configurations of oxygen vacancies.     

Dielectronic recombination rate coefficients for the Ni ${\sf I}$ isoelectronic sequence

Ab initio calculations of the total dielectronic recombination (DR) rate coefficients for thirteen ions along the NiI isoelectronic sequence in the ground state (Kr⁸⁺, Mo¹⁴⁺, Ag¹⁹⁺, Sn²²⁺, Xe²⁶⁺, Nd³²⁺, Gd³⁶⁺, Yb⁴²⁺, W⁴⁶⁺, Au⁵¹⁺, Pb⁵⁴⁺, At⁵⁷⁺, and U⁶⁴⁺) have been performed using the flexible atomic code. The level-by-level calculations are performed for evaluating the DR contributions through the relevant Cu-like autoionizing inner-shell excited 3l¹⁷4l^′n^′′l^′′ and 3l¹⁷5l^′n^′′l^′′ configuration complexes with n^′′ ≤15, which are associated with Δn=1 and Δn=2 core-excitations, respectively. The usual (n^′′)^-3 scaling law is found to be invalid for low-Z ions. A level-by-level extrapolation procedure is employed to obtain the contributions through higher n^′′ complexes. The decays to autoionizing levels followed possibly by radiative cascades could enlarge the rates at relatively high temperature by a factor up to about 23%. For the whole isoelectronic ions the contributions from 3s²3p⁶3d⁹ 4l^′n^′′l^′′ dominate the total DR rates while the contributions from the 3s²3p⁶3d⁹ 5l^′n^′′l^′′ configuration complexes are about 10-20% at relatively high temperature. On the basis of the calculated results, a general analytic formula for the total DR rate coefficients of all the ions with 36≤Z ≤92 along the NiI isoelectronic sequence is constructed. The comparisons of the rates obtained from the general formula with those from the detailed calculations show that the formula is of high precision, generally better than 3% accuracy for electron temperatures kT≥0.1E_I, where E_I is the ionization energy of the Cu-like ion. The present DR rates at temperature above 1.0E_I are larger than the previously published data by a factor above 30%. The commonly used semiempirical formula proposed by Burgess and modified by Merts may overestimate the rates at high temperature by a factor of about 2 for low-Z ions.     

类镍等电子系列离子M1,M2,E2禁戒跃迁特性的理论研究

利用基于全相对论框架下的多组态Dirac-Fock理论方法发展起来的程序包GRASP92和新发展的处理辐射跃迁过程的程序REOS99，计算了类镍等电子系列离子(Z=45—95)的基组态3s²3p⁶3d¹⁰¹S₀以及低激发组态3s²3p⁶3d⁹4l,3s²3p⁵3d¹⁰4l和3s3p⁶3d¹⁰4l(l=s,p,d,f)的能级及其向基态的M1,M2,E2禁戒跃迁概率.通过分析高离化类镍离子在特定的原子序数范围内由于存在能级交叉而产生的强组态相互作用，解释了高离化类镍离子禁戒跃迁概率的反常变化现象，探讨了禁戒跃迁概率受强组态相互作用影响而变化的一般规律.     

Computational study of collisional energy transfer and quasi-continuous population inversions in laser-pumped Ca vapor

A computational study of population inversion between several pairs of excited states viz 3d4p ³ F-4s3d ³ D, 4s5s ³ S-4s4p ³ P and 4s3d ³ D-4s4p ³ P in Ca vapor pumped on the 4s ^{2 1} S ₀-4s4p ³ P ₁ transition is presented. The main aim is to investigate the influence of various atomic processes in creating and sustaining the population inversion for long times after the excitation pulse. The delicate interplay between superelastic energy transfer to free electrons, energy pooling collisions and cascaded recombination is particulary examined. It is noted that quasi-continuous population inversion can be readily excited on the 4s3d ³ D-4s4p ³ P transitions; and under some conditions, also on the 4s5s ³ S-4s4p ³ P transitions. Furthermore, inversion on the 3d4p ³ F-4s3d ³ D transitions can also be excited for a considerable length of time. The results may be useful in designing and developing quasi-cw metal vapor lasers.     

Spin-polarized Dirac-Slater calculations on the energies of hollow argon atom

In this work, the multiplet splitting in terms of a spin-dependent model is analyzed. The spin-polarized and unpolarized single configuration Dirac-Fock-Slater wavefunctions have been used in the evaluation of the total energies of highly ionized argon with different L shell population The transition energies of hollow argon atom with initial configurations 1s ⁰ _1/22s ^m _1/22p ⁿ _1/22p ^l _3/2 with m = 0 to 2 and n + l varying from 6 to 1 are reported in this work. The calculations have been carried out by taking into account a relativistic exchange potential in the Dirac-Slater potential. To account for the correlation effects, a correction term has also been considered perturbatively. The present calculations show that the spin-polarized technique which is mainly applied to the ground states of atoms may also be applied to atoms ionized in the inner shells with a good degree of accuracy. Received 5 December 2000 and Received in final form 9 April 2001     

Additional symmetry for the electronic shell in its ground state and many-electron effects

The additional symmetry for the properties related to the ground state of the atom is considered taking into account many-electron effects. Calculations of the I _4f, I _3d,I _2p,I _3p binding energies, 4f ^N-15d - 4f^N system differences and 2p, 3p electron affinities in the second order of perturbation theory and in the configuration interaction approximation have been performed for the ground configurations with one open shell. The analysis of separate many-electron corrections for these quantities and their variation along the sequences of atoms and ions shows that the main corrections maintain the considered symmetry. Received 18 January 1999 and Received in final form 17 July 1999     

Crossed-second-order specific-mass isotope shift in the Nickel atom

The crossed-second-order corrections to the specific mass shifts of the lowest terms of the two lowest configurations of the Nickel atom are evaluated ab initio in the Multiconfigurational Hartree-Fock scheme. The excitations towards the nf(l=3) empty subshells play the major role. If the contributions obtained are added to the Hartree-Fock values, the discrepancy between experiment and theory for the 3d ⁸ 4s ²?3d ⁹ 4s (virtual) transition is only reduced by one third. As concerns the differences between the specific shifts of the five Russell-Saunders terms of 3d ⁸ 4s ², the crossed-second-order contributions are predicted to be practically as large as the Hartree-Fock values, which makes the total definitely measurable.     

Cu-like Pd and Ag inner-shell photoionization phenomena

We have obtained results for converting focused laser radiation to X-ray line emissions in laser-heated NaF and Cu plasmas. These plasmas were used as the pump source for studying the phenomena of inner-shell photoionization of Zn-like ionic states. Soft X-ray emissions from transitions of 3d ⁹4s ² 3d ¹⁰4p in Cu-like Pd and Ag ions were observed.     

Fine-structure energy levels, oscillator strengths and lifetimes in Co XV

Excitation energies from ground state for 97 fine-structure levels as well as oscillator strengths and radiative decay rates for all electric-dipole-allowed and intercombination transitions among the fine-structure levels of the terms belonging to the (1s ²2s ²2p ⁶)3s ²3p, 3s ³ p ², 3s ²3d, 3p ³, 3s3p3d, 3p ²3d, 3s3d ², 3s ²4s, 3s ²4p, 3s ²4d, 3s ²4f, and 3s3p4s configurations of Co XV are calculated, using extensive configuration-interaction (CI) wave functions, obtained with the CIV3 computer code of Hibbert. The important relativistic effects in intermediate coupling are included through the Breit-Pauli approximation via spin-orbit, spin-other-orbit, spin-spin, Darwin and mass correction terms. Small adjustments to the diagonal elements of the Hamiltonian matrices have been made. Our calculated excitation energies, including their ordering, are in excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology (NIST) wherever available. The mixing among several fine-structure levels is found to be very strong, with most of the strongly mixed levels belonging to the (1s ²2s ²2p ⁶)3p ²3d and 3s3d ² configurations. The strong mixing among several fine-structure levels makes it very difficult to identify them uniquely. Perhaps, that may be the reason for the lack of both experimental and theoretical results for these levels. We believe that our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work. From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. In this calculation we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.     

Radiative lifetimes in Ce I and Ce II

New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity levels belonging to the 4f5d^26p and 4f ²5d ² configurations of Ce I and 6 even-parity levels belonging to the 5d^26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II levels range in energy from 26 545 to 29 102 cm^-1, and 42 573 to 48 152 cm^-1, respectively. Received 25 September 2002 Published online 4 March 2003     

Resonance excitation process for Ni-like gold

A detailed and large-scale calculation on the resonant excitation rate coefficients from the ground state to the 106 fine-structure levels belonging to 3l¹⁷4l^′(l=0,1,2;l^′=0,1,2,3) configurations of Ni-like gold have been performed using the relativistic distorted-wave approximation. The contributions through all possible Cu-like doubly excited states 3l¹⁷4l^′n^″l^″and 3l¹⁷5l^′n^″l^″(n^″≤15,l^″≤8) are calculated explicitly. The radiative damping effects on resonant excitation rates are studied. Significant effects arising from decays to autoionizing levels are also investigated. The n⁻³scaling law is investigated and is used to obtain the contributions from high-n configurations. Contributions from resonant excitation are found to be as important as direct excitation processes for most transitions. In some cases, resonant excitation can enhance the excitation rate coefficients by an order of magnitude. In addition, the total dielectronic recombination rate coefficients of Ni-like gold are also presented and compared with other works.     

Shell effects for isovector <Emphasis Type="Italic">l</Emphasis>-forbidden <Emphasis Type="Italic">M</Emphasis>1 transitions in odd nuclei

It is inferred from the analysis of the experimental data that the reduced probabilities of isovector l-forbidden M1 transitions achieve maximum values in nuclei with a magic core. The minimum values are related to γ transitions in nuclei belonging to the region of stable deformation with A ≈ 25. Isovector l-forbidden M1 transitions in mirror nuclei are explored. The ratio of the reduced probabilities for proton and neutron transitions shows the maximum deviation from the theoretical evaluations for the pair of nuclei ⁴¹Ca-⁴¹Sc consisting of the even-even magic core ⁴⁰Ca and one nucleon outside the closed 1d2s shell.