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Energy levels of 30 low-lying states of Lu2+ and allowed electric-dipole matrix elements between these states are evaluated using a relativistic all-order method in which all single, double and partial triple excitations of Dirac-Fock wave functions are included to all orders of perturbation theory. Matrix elements are critically evaluated for their accuracy and recommended values of the matrix elements are given together with uncertainty estimates. Line strengths, transition rates and lifetimes of the metastable 5d(3/2) and 5d(5/2) states are calculated. Recommended values are given for static polarizabilities of the 6s, 5d and 6p states and tensor polarizabilities of the 5d and 6p(3/2) states. Uncertainties of the polarizability values are estimated in all cases. The blackbody radiation shift of the 6s(1/2)-5d(5/2) transition frequency of the Lu2+ ion is calculated with the aid of the recommended scalar polarizabilities of the 6s(1/2) and 5d(5/2) states. Finally, A and B hyperfine constants are determined for states of 175Lu2+ with n

Motivated by recent interest in their applications, we report a systematic study of Cs atomic properties calculated by a high-precision relativistic all-order method. Excitation energies, reduced matrix elements, transition rates, and lifetimes are determined for levels with principal quantum numbers $n \leq 12$ and orbital angular momentum quantum numbers $l \leq 3$. Recommended values and estimates of uncertainties are provided for a number of electric-dipole transitions and the electric dipole polarizabilities of the $ns$, $np$, and $nd$ states. We also report a calculation of the electric quadrupole polarizability of the ground state. We display the dynamic polarizabilities of the $6s$ and $7p$ states for optical wavelengths between 1160 nm and 1800 nm and identify corresponding magic wavelengths for the $6s-7p_{1/2}$, $6s-7p_{3/2}$ transitions. The values of relevant matrix elements needed for polarizability calculations at other wavelengths are provided., Comment: 10 pages, 6 figures

Excitation energies of ns1/2, npj, and ndj states in Cd+ (n = 5), Hg+ (n = 5) and ns1/2, npj, and (n – 1)dj states in Ca+ (n = 4), Sr+ (n = 5), and Ba+ (n = 6) are evaluated using the linearized coupled-cluster (all-order) method. Reduced matrix elements, oscillator strengths, and transition rates are determined for the ns–npj–ndj (or ns–npj–(n – 1)dj) possible electric dipole transitions in Ca+, Sr+, Ba+, Cd+, and Hg+. Electric quadrupole matrix elements are evaluated to obtain ns1/2–(n – 1)dj transition rates in Ca+ (n = 5), Sr+ (n = 5), and Ba+ (n = 6). The matrix elements are calculated using both relativistic many-body perturbation theory, complete through third order, and the relativistic all-order method restricted to single and double (SD) excitations. The SD lifetime results for the np and nd states in Ca+, Sr+, Ba+, Cd+, and Hg+, are compared with the latest available experimental measurements. The contribution of the magnetic dipole nd3/2–nd5/2 transition to the lifetimes of the lowest nd5/2 level ln Ca+, Sr+, and Ba+ ions is discussed. These calculations provide a theoretical benchmark for comparison with experiment and theory as well as data needed for various applications.

Energies of [Kr]4d94f2, [Kr]4d94f5l, and [Kr]4d95l5l′ states (with l = s, p, d, f) for Ag-like ions with Z = 50–100 are evaluated to second order in relativistic many-body perturbation theory (RMBPT) starting from a Pd-like Dirac–Fock potential ([Kr]4d10). Second-order Coulomb and Breit–Coulomb interactions are included. Correction for the frequency dependence of the Breit interaction is taken into account in lowest order. The Lamb-shift correction to energies is also included in lowest order. Intrinsic particle–particle–hole contributions to energies are found to be 20–30% of the sum of the one- and two-body contributions. Transition rates and line strengths are calculated for the 4d–4f and 4d–5l electric-dipole (E1) transitions in Ag-like ions with nuclear charge Z = 50–100. RMBPT including the Breit interaction is used to evaluate retarded E1 matrix elements in length and velocity forms. First-order RMBPT is used to obtain intermediate coupling coefficients and second-order RMBPT is used to calculate transition matrix elements. A detailed discussion of the various contributions to the dipole matrix elements and energy levels is given for silverlike tungsten (Z = 74). The transition energies included in the calculation of oscillator strengths and transition rates are from second-order RMBPT. Trends of the transition rates as functions of Z are illustrated graphically for selected transitions. Additionally, we perform calculations of energies and transition rates for Ag-like W by the Hartree–Fock relativistic method (Cowan code) and the Multiconfiguration Relativistic Hebrew University Lawrence Atomic Code (HULLAC code) to compare with results from the RMBPT code. These atomic data are important in modeling of N-shell radiation spectra of heavy ions generated in various collision as well as plasma experiments. The tungsten data are particularly important for fusion application.PACS Nos.: 31.15.A–, 31.15.ag, 31.15.am, 31.15.aj

We optically excite the electronic state 3s3p ^{3}P_{0} in ^{24}Mg atoms, laser cooled and trapped in a magic-wavelength lattice. An applied magnetic field enhances the coupling of the light to the otherwise strictly forbidden transition. We determine the magic wavelength, the quadratic magnetic Zeeman shift, and the transition frequency to be 468.46(21) nm, -206.6(2.0) MHz/T^{2}, and 655 058 646 691(101) kHz, respectively. These are compared with theoretical predictions and results from complementary experiments. We also develop a high-precision relativistic structure model for magnesium, give an improved theoretical value for the blackbody radiation shift, and discuss a clock based on bosonic magnesium.

We measure optical spectra of Nd-like W, Re, Os, Ir, and Pt ions of particular interest for studies of a possibly varying fine-structure constant. Exploiting characteristic energy scalings we identify the strongest lines, confirm the predicted 5s-4f level crossing, and benchmark advanced calculations. We infer two possible values for optical M2/E3 and E1 transitions in Ir^{17+} that have the highest predicted sensitivity to a variation of the fine-structure constant among stable atomic systems. Furthermore, we determine the energies of proposed frequency standards in Hf^{12+} and W^{14+}.

Excitation energies, line strengths, oscillator strengths, and transition probabilities are calculated for 4d–14f, 4d–15p, 4d–15f, and 4d–16p hole–particle states in Pd-like ions with nuclear charges Z ranging from 49 to 100. Relativistic many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a [Kr] 4d10 closed-shell Dirac–Hartree–Fock (DHF) potential and include second- and third-order Coulomb corrections and second-order Breit–Coulomb corrections. First-order perturbation theory is used to obtain intermediate-coupling coefficients and second-order MBPT is used to determine matrix elements. Contributions from negative-energy states are included in the second-order electric-dipole matrix elements. The resulting transition energies, line strengths, and transition rates are compared with experimental values and with other recent calculations. Trends of oscillator strengths as functions of nuclear charge Z are shown graphically for all transitions from the 4d–14f, 4d–15p, 4d–15f, and 4d–16p states to the ground state. PACS Nos.: 31.15.Ar, 31.15.Md, 32.70.Cs, 32.30.Rj, 31.25.Jf

M-shell spectra of W ions have been produced at the Lawrence Livermore National Laboratory EBIT-II electron beam ion trap-II at different energies of the electron beam. A survey has been performed at 2.4, 2.8, and 3.6 keV, and for steps in energy of 100 eV over the 3.9–4.6 keV energy range. The analysis of 11 W spectra has shown the presence of a wide variety of ionization stages from Se-like to Cr-like W; the appearances of these ionization stages correlate well with the energy of their production. The present paper focuses on the identification of 63 experimental features of W ions in a spectral region from 5 to 6 Å (1 Å = 10–10 m) using calculations with inclusion of all ionization stages matching this spectral region. The majority of lines in all spectra have been identified and assigned to the 4f → 3d and 4d → 3p transitions. This is the first work that lists a comprehensive identification of so many resolved spectral features of X-ray M-shell transitions in W ions recorded in such detail in the laboratory. PACS Nos.: 52.58.Lq,32.30.Rj,52.70.La

Energies of 1s2l2l′ and 1s3l3l′ states for Li-like ions with Z = 6–100 are evaluated to second order in relativistic many-body perturbation theory. Second-order Coulomb and Breit–Coulomb interactions are included. The calculations start with a Dirac potential and include all possible 1s2l2l′ and 1s3l3l′ configurations. Correction for the frequency dependence of the Breit interaction is taken into account in lowest order. The Lamb-shift correction to the energies is also included in lowest order. A detailed discussion of the various contributions to the energy levels is given for Li-like iron (Z = 26). We found that the three-electron corrections to the energy contribute about 10–20% of the total second-order energy. Comparisons are made with available experimental data and excellent agreement for term splitting is obtained even for low-Z ions. These calculations are presented as a theoretical benchmark for comparison with experiment and theory.PACS Nos.: 32.30.Rj, 32.70.Cs, 31.25.Jf, 31.15.Md

Reduced matrix elements, oscillator strengths, and transition rates are calculated for all allowed and forbidden 1s2l′ 2l′ ′ – 1s 22l electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions in lithiumlike ions with nuclear charges ranging from Z = 6 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded E1, M1, E2, and M2 matrix elements. The calculations start with a Dirac potential and include all possible 1s2l′ 2l′ ′ configurations, leading to seven odd-parity and nine even-parity states. First-order perturbation theory is used to obtain intermediate coupling coefficients. Second-order RMBPT is used to determine the matrix elements, which are evaluated for the 22, 20, 16, and 18 possible E1, M1, E2, and M2 transitions, respectively. A detailed discussion of the various contributions to the energy levels and E1, M1, E2, and M2 matrix elements is given for lithiumlike iron, Z = 26. Th...

A relativistic many-body method is developed to calculate energy and transition rates for multipole transitions in many-electron ions. This method is based on relativistic many-body perturbation theory (RMBPT), agrees with MCDF calculations in lowest order, includes all second-order correlation corrections, and includes corrections from negative-energy states. Reduced matrix elements, oscillator strengths, and transition rates are calculated for electric-dipole (E1) and electric-quadrupole (E2) transitions, and magnetic-dipole (M1) and magnetic-quadrupole (M2) transitions in Ni-like ions with nuclear charges ranging from Z = 30 to 100. The calculations start from a 1s22s22p63s23p63d10 Dirac–Fock potential. First-order perturbation theory is used to obtain intermediate-coupling coefficients, and second-order RMBPT is used to determine the matrix elements. The contributions from negative-energy states are included in the second-order E1, M1, E2, and M2 matrix elements. The resulting transition energies and transition rates are compared with experimental values and withresults from other recent calculations.PACS Nos.: 32.30.Rj, 32.70.Cs, 32.80.Rm, 34.70.+e

Transition rates, oscillator strengths, and line strengths are calculated for electric-dipole (E1) transitions between even-parity 3s3p2, 3s23d, 3p23d, 3d23s, and 3d3 states and odd-parity 3s23p, 3p3, 3s3p3d, and 3d23p states in Al-like ions with the nuclear charges ranging from Z=15 to 100. Relativistic many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a 1s22s22p6 Dirac–Fock potential. First-order MBPT is used to obtain intermediate coupling coefficients and second-order MBPT is used to calculate transition matrix elements. Contributions from negative-energy states are included in the second-order E1 matrix elements to ensure gauge-independence of transition amplitudes. Transition energies used in the calculation of oscillator strengths and transition rates are from second-order MBPT. Transition rates, line strengths, and oscillator strengths are compared with critically evaluated experimental values and with results from other recent calculations. We present data for selected transitions between 10 of the possible 73 even-parity 3s3p2, 3s23d states and 29 of the possible 75 odd-parity 3s23p, 3p3, and 3s3p3d states in Al-like ions. Trends of the transition rates as functions of Z are illustrated graphically for 220 of the 3220 possible transitions. Lifetimes of the 10 even-parity lower levels and the 27 odd-parity upper levels are given for Z=15–100.

The University of Nevada, Reno has developed a collisional-radiative atomic kinetics model that has successfully described the spectra produced by widely different multicharged ion experiments. The application of the model to experiments that highlight the importance of particular kinetics effects, including time-dependence and non-Maxwellian electron distribution functions, will be presented. These experiments include ion beam collision and high-temperature femtosecond laser and X-pinch plasma experiments. Adequate descriptions of ion beam collision spectra and x-ray yield require time-dependent treatment of radiative cascades from high-n capture states. Spectra from plasmas with significant fractions of hot electrons, such as those produced by fs lasers and X-pinches, require calculation of hot electron effects on collisional rates. The kinetics model presented here extracts as much information as possible from advanced experimental diagnostics such as time- and space-resolved spectral measurements.

X-ray spectra of high energy density (HED) Z-pinch plasmas have been analyzed by means of a comprehensive kinetic modeling. A new diagnostic, x-ray spectropolarimetry, was applied to study anisotropy of Z-pinch plasma. This diagnostic is based on theoretical modeling of polarization-dependent spectra measured simultaneously by spectrometers with different sensitivity to polarization. Specifically, K-shell emission from Ti X-pinches was recorded simultaneously with identical LiF crystal spectrometers with the dispersion plane perpendicular and parallel to the discharge axis. Spectroscopic results from seven Ti X-pinch shots have been analyzed. Similar K-shell Ti polarization-dependent spectra generated by a quasi-Maxwellian electron beam at the LLNL EBIT-II electron beam ion trap have been studied. Further, the EBIT-II M-shell W spectra have proved to be important in the development of M-shell diagnostics of HED Z-pinch plasma. The advantages provided by electron beam ion trap data in the interpretation of HED Z-pinch spectra will be presented.

We calculate energy levels, radiative transition probabilities, and autoionization rates for Be-like oxygen (O4+) including 1s2 2lnl' (n = 2–8, l [Formula: see text] n – 1) and 1s23l' nl (n = 3–6, l [Formula: see text] n – 1) states by the multiconfigurational Hartree–Fock method (Cowan code) and the perturbation theory Z-expansion method (MZ code). The state selective dielectronic recombination-rate coefficients to excited states of Be-like oxygen are obtained, which are useful for modeling O V spectral lines in a recombining plasma. Configuration mixing plays an important role for the principal quantum number, n, distribution of the dielectronic recombination-rate coefficients for 2snl (n [Formula: see text] 5) levels at low electron temperature. The orbital angular momentum quantum number, l, distribution of the rate coefficients shows a peak at l = 4. The total dielectronic recombination-rate coefficient is derived as a function of electron temperature. The dielectronic satellite lines are also obtained. PACS Nos.: 34.80Lx, 32.80Dz, 32.30Jc, 31.10+z

M X-rays have been observed from 1–40 keV/u 181Taq+ (q = 45–49) ions colliding with neutral Ar atoms under single collisions. The most dominant X-rays have been found to be due to transitions of 4p–3d and 4f–3d when the projectiles bring 3d-shell vacancies into collisions. Though much weaker, M X-rays also have been observed in collisions with Ta45+ ions that initially have no 3d-shell vacancy and are understood to originate from transitions of the doubly excited states 3d9nln'l' formed through strong electron–electron interactions after single-electron capture. The observed M X-ray spectra have been compared and reproduced nicely with the synthesized spectra. It has been confirmed that transitions of such doubly excited states also contribute to X-rays at the lower energy region observed even for higher charge ions with 3d vacancies. PACS Nos.: 32.30Rj, 32.70Cs, 32.80Rm, 34.70+e

Several peaks have been observed, in the electron energy range up to 20 eV, due to Coster-Kronig electrons from the autoionizing Rydberg states emitted from 2 MeV u-1 Si5+ ions excited through a carbon foil. To obtain a better understanding of these low-energy electron spectra and their production mechanisms, we synthesize the expected electron spectrum which is compared with the observed electron spectrum. Two theoretical methods, namely the perturbation theory of Z-expansion (MZ code) and the multiconfiguration Hartree-Fock method (Cowan code), are used to calculate the necessary Auger electron energies and emission rates. It has been found that the 1s22pnl-1s22s 2S and 1s22s2pnl-1s22s2 1S decays give the most significant contributions to the observed electron spectrum from threshold up to the 20 eV region. The synthetic electron spectra have also been found to reproduce the observed electron spectra quite nicely when the charge distributions of the projectile Si ions after thin carbon foils are taken into account.

X-rays have been observed in collisions of low-energy (keV/u), highly charged Xeq+ (q = 26–43) ions with neutral Ar atoms. These X-rays are understood to be produced through electron capture by highly charged projectile ions from target atoms, the electrons then cascade down to the ground state. It is clearly noted that the most intense X-ray peaks correspond to M-shell – N-shell transitions with different numbers of M-shell vacancies and that X-ray intensities decrease significantly toward high energies near the ionization limit. This observation indicates that the direct transition of an electron captured in a highly excited state to M-shell vacancies is negligibly small. To obtain a better understanding of X-ray production mechanisms, we tried to synthesize the expected X-ray spectrum and compare that with the observed spectrum. The synthesized spectra were found to reproduce the observed spectra reasonably well. PACS Nos: 32.30Rj, 32.70Cs, 32.80Rm, 34.70+e

A high-precision relativistic calculations of Cd-like Nd$^{12+}$, Sm$^{14+}$ and Sn-like Pr$^{9+}$, Nd$^{10+}$ atomic properties is carried out using an approach that combines configuration interaction and a linearized coupled-cluster method. These ions have long-lived metastable states with transitions accessible by laser excitations, relatively simple electronic structure, high sensitivity to $\alpha$ variation, and stable isotopes. Breit and QED corrections were included into the calculations. Energies, transition wavelengths, electric- and magnetic-multipole reduced matrix elements, lifetimes, and sensitivity coefficients $q$ and $K$ to the variation of the fine-structure constant $\alpha$ were obtained. A detailed study of uncertainties was performed. Energies for similar Cd-like Ba$^{8+}$, La$^{9+}$, Ce$^{10+}$, Pr$^{11+}$ and Sn-like Ba$^{6+}$ ions were calculated and compared with experiment for further tests of the accuracy., Comment: 13 pages. arXiv admin note: text overlap with arXiv:1407.8272

We carried out a detailed high-precision study of Ag-like ${\mathrm{Nd}}^{13+}$ and ${\mathrm{Sm}}^{15+}$ and In-like ${\mathrm{Ce}}^{9+}$, ${\mathrm{Pr}}^{10+}$, ${\mathrm{Nd}}^{11+}$, ${\mathrm{Sm}}^{13+}$, and ${\mathrm{Eu}}^{14+}$ highly charged ions. These ions were identified to be of particular interest for the development of ultra-accurate atomic clocks, the search for variation of the fine-structure constant $\ensuremath{\alpha}$, and quantum information [Safronova et al., Phys. Rev. Lett. 113, 030801 (2014)]. The relativistic linearized coupled-cluster method was used for Ag-like ion calculations, and a hybrid approach that combines configuration interaction and a variant of the coupled-cluster method was used for the In-like ion calculations. Breit and QED corrections were included. Energies, transition wavelengths, electric-dipole, electric-quadrupole, electric-octupole, magnetic-dipole, magnetic-quadrupole, and magnetic-octupole reduced matrix elements, lifetimes, and sensitivity coefficients to $\ensuremath{\alpha}$ variation were calculated. A detailed study of various contributions was carried out to evaluate uncertainties of the final results. Energies for several similar ``reference'' ions where the experimental values are available were calculated and compared with experiment for further tests of the accuracy.

Excitation energies of the [Xe]$nd$ ($n=5\ensuremath{-}9$), [Xe]$ns$ ($n=6\ensuremath{-}10$), [Xe]$np$ ($n=6\ensuremath{-}9$), [Xe]$nf$ ($n=4\ensuremath{-}8$), and [Xe]$ng$ ($n=5\ensuremath{-}8$) states in La iii, where [Xe] = $1{s}^{2}2{s}^{2}2{p}^{6}3{s}^{2}3{p}^{6}3{d}^{10}4{s}^{2}4{p}^{6}4{d}^{10}5{s}^{2}5{p}^{6}$, are evaluated. Electric dipole matrix elements for the allowed transitions between the low-lying [Xe]$nd$, [Xe]$ns$, [Xe]$np$, [Xe]$nf$, and [Xe]$ng$ states in the La iii ion are calculated using the high-precision relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Recommended values are provided for a large number of electric dipole matrix elements, oscillator strengths, transition rates, and lifetimes. Scalar and tensor polarizabilities of the states listed above are evaluated. The uncertainties of the recommended values are estimated. Electric quadrupole and magnetic dipole matrix elements are calculated to determine lifetimes of the $5{d}_{5/2}$ and $6s$ metastable levels. The ground-state $E1$, $E2$, and $E3$ static polarizabilities are calculated. This work provides recommended values critically evaluated for their accuracy for a number of La iii atomic properties for use in planning and analysis of various experiments as well as theoretical modeling.

We propose 10 highly charged ions as candidates for the development of next generation atomic clocks, quantum information, and search for $\ensuremath{\alpha}$ variation. They have long-lived metastable states with transition wavelengths to the ground state between 170--3000 nm, relatively simple electronic structure, stable isotopes, and high sensitivity to $\ensuremath{\alpha}$ variation (e.g., ${\mathrm{Sm}}^{14+}$, ${\mathrm{Pr}}^{10+}$, ${\mathrm{Sm}}^{13+}$, ${\mathrm{Nd}}^{10+}$). We predict their properties crucial for the experimental exploration and highlight particularly attractive systems for these applications.

Ejected electron spectra from the singlet and triplet states of doubly excited Ne6+**(1s22pnl), Ne6+**(1s23l3l') and Ne6+**(1s23l4l') ions, produced by 80 keV Ne8+(1s2) + He, Ne and Ar collisions, have been measured by means of a zero-degree electron spectroscopy. Only singlet states were observed when the target was He. In contrast, the contribution from the triplet states prevailed in the spectra for the Ne target. For the Ar target, practically no signals were observed in the energy region for the 1s23lnl' states. Two theoretical methods, the perturbation theory (MZ code) and the multi-configurational Hartree-Fock (Cowan code) were used for identification of ejected-electron spectra. Using the (j) string analysis in the extended classical over-barrier model, we discuss the possibility of the participation of inner electrons in the process of double-electron capture by highly charged ion multi-electron target atoms.

Relativistic calculations of nonradiative transition rates to K -, L -, and M -shell vacancy states in Ni-, Cu-, and Zn-like ions with Z =32, 36, 42, 47, 56, 60, 66, 74, 83, and 92 are performed. Auger and Coster–Kronig transition probabilities are calculated using both Dirac–Hartree–Fock and model-potential wave functions. Tabulated data are presented for K - and L -shell Auger rates in Ni-, Cu-, and Zn-like ions, for M -shell Auger rates in Zn-like ions, and for L - and M -shell Coster–Kronig rates in Cu-like ions. Results obtained by averaging over angular momentum substates are also presented and semiempirical formulas are given for the average rates.

The relative intensities of dielectronic satellite lines determined by radiative transition probabilities and autoionization rates are calculated for the transitions 2lnl' – 1snl'', 2lnl' – 1s2l (n = 4–5, l' = 0–3, l'' = 0–3, l = 0–1) in He-like ions and for the transitions 1s2lnl' – 1s2nl'', 1s2lnl' – 1s22l (n = 4–5, l' =0–3, l'' = 0–3, l = 0–1) in Li-like ions, for all Z = 5–54, using the perturbation theory method (Z-expansion). Relativistic effects are taken into account using the Breit–Pauli operators. The asymptotic dependence on n of the energy matrix is discussed for 2lnl' and 1s2lnl' autoionizing states. The intermediate coupling coefficients obtained after diagonalization of the energy matrices are also studied. It was observed that these coefficients change very sharply with n and Z due to a redistribution of the contributions of relativistic and correlation effects. As a result, all other atomic characteristics (radiative and nonradiative transition rates, branching ratios, and relative intensity factor) display nonmonotonic Z- and n-dependencies with maxima and minima. PACS Nos.: 32.80D, 31.20G, 31.30J, 31.50

Energy levels, radiative transition probabilities and autoionization rates for Be-like Ne (Ne6+) including 1s22pnl (n = 2-9, l n-1) and 1s23l´nl (n = 3-6, l n-1) states are calculated. Two theoretical methods, the perturbation theory Z-expansion (MZ code) method and the multi-configurational Hartree-Fock (Cowan code) method, are used for the calculations. Autoionizing levels above the 1s22s and 1s22p thresholds are considered and their contributions computed. The state-selective dielectronic recombination rate coefficients from Li-like Ne (Ne7+) ions to Be-like Ne (Ne6+) ions for bound states of Ne6+ ions are obtained. Configuration mixing plays an important role for the principal quantum number, n, distribution of the dielectronic recombination rate coefficients for n6 levels. The orbital angular momentum quantum number, l, distribution of the rate coefficients shows a peak around l = 4-5. The rate coefficients for the excited states with higher n are extrapolated using a scaling law. The total dielectronic recombination rate coefficients are derived as a function of electron temperature.

Transition rates, oscillator strengths, and line strengths are calculated for the 49 possible electric-dipole transitions between the eight even-parity 2s2p{sup 2} states and the seven odd-parity 2s{sup 2}2p and 2p{sup 3} states in boronlike ions with nuclear charges ranging from Z=6 to 100. Relativistic many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded E{sub 1} matrix elements in length and velocity forms. The calculations start from a 1s{sup 2} Dirac-Fock potential. First-order MBPT is used to obtain intermediate coupling coefficients and second-order MBPT is used to calculate transition matrix elements. Contributions from negative-energy states are included in the second-order E{sub 1} matrix elements to ensure gauge independence of transition amplitudes. The transition energies used in the calculation of oscillator strengths and transition rates are from second-order MBPT. Transition rates, line strengths, and oscillator strengths are compared with critically evaluated experimental values and with results from other recent calculations. Lifetimes of the five possible odd-parity upper levels and the five possible even-parity upper levels are given for Z=6{endash}100. Trends of the transition rates as functions of {ital Z} are illustrated graphically for selected transitions. thinsp {copyright} {ital 1999} {ital The American Physical Society}

Reduced matrix elements, oscillator strengths, and transition rates are calculated for 2l12l2[LSJ]-2l33l4[L´S´J´] electric-dipole transitions in beryllium-like ions with nuclear charges Z from 6 to 100. Many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded dipole matrix elements in length and velocity forms. The calculations start with a 1s2 Dirac-Fock potential and include all possible n = 2 and n = 3 configurations. We use first-order perturbation theory to obtain intermediate coupling coefficients and second-order MBPT to determine matrix elements. The transition energies used to evaluate transition probabilities are also obtained from second-order MBPT. The importance of negative-energy contributions to the transition amplitudes in maintaining gauge independence is discussed. Our results for 2s3p 1,3P1-2s2 1S0 transitions are compared with available theoretical and experimental data throughout the isoelectronic sequence. Rates for 2l3l´ [J = 1]-2s2 1S0, 2l3l´ [J = 1]-2p2 1S2, 2l3l´ [J = 1]-2s2p 1P1, and 2l3l´ [J = 2]-2s2p 1P1 transitions are given graphically for all Z.

Reduced matrix elements and transition rates are calculated for all magnetic dipole (M1) transitions within 2l2l' configurations and for some 2l3l' - 2l2l' transitions in Be-like ions with nuclear charges ranging from Z = 4 to 100. Many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded M1 matrix elements. The calculations start with a (1s)2 Dirac-Fock potential and include all possible n = 2 configurations, leading to 4 odd-parity and 6 even-parity states, and some n = 3 configurations. First-order perturbation theory is used to obtain intermediate coupling coefficients. Second-order MBPT is used to determine the matrix elements, which are evaluated for all 11 M1 transitions within 2l2l' configurations and for 35 M1 transitions between 2l3l' and 2l2l' states. The transition energies used in the calculation of oscillator strengths and transition rates are obtained from second-order MBPT. The importance of negative-energy contributions to M1 transition amplitudes is discussed.

Absolute energies of the autoionizing states 1s2s22pn [LSJ] with n = 3–6, 1s2s2pn [LSJ] with n = 4–6 and 1s2pn [LSJ] with n = 5–6, and non-autoionizing states 1s22s2pn [LSJ] with n = 2–6, 1s22s2pn [LSJ] with n = 3–6, and 1s22pn [LSJ] with n = 4–6 were calculated for ions with a nuclear charge Z = 6–54 by using the 1/Z perturbation theory method. These states were considered as the states with one or few holes in the Ne-like core state 1s22s22p6. Relativistic corrections were taken into account in the frame of the Breit operators. The autoionization rates for the above-mentioned autoionizing states and ions were computed as well and are shown in grafic forms as Z-dependences. These new atomic data represent an important material, which can be used in different areas of atomic and plasma physics involving the study of multiply-charged ions.

Reduced matrix elements, oscillator strengths, and transition rates are calculated for all allowed and forbidden 2s–2p electric dipole transitions in berylliumlike ions with nuclear charges ranging from Z = 4 to 100. Many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start with a 1s2 Dirac–Fock potential and include all possible n = 2 configurations, leading to 4 odd-parity and 6 even-parity states. First-order perturbation theory is used to obtain intermediate coupling coefficents. Second-order MBPT is used to determine the matrix elements, which are evaluated for the 16 possible E1 transitions. The transition energies used in the calculation of oscillator strengths and transition rates are evaluated using second-order MBPT. The importance of virtual electron–positron pair (negative energy) contributions to the transition amplitudes is discussed.

Energies of the ten (2l2l') states of ions of the beryllium isoelectronic sequence are determined to second order in relativistic many-body perturbation theory starting from hydrogenic basis functions. Both the second-order Coulomb interaction and the second-order Breit-Coulomb interaction are included. Each diagram contribution is represented as a power series in Z. The leading term of each diagram gives the nonrelativistic limit which coincides with the contribution obtained starting with nonrelativistic basis functions. We obtain numerical data for the relativistic corrections for 2l states of Li-like ions and for (2l2l') states of Be-like ions.

Energy levels and autoionizing rates of 2lnl' (n = 3–12, l = 0–4) configurations for He-like ions with Z = 4–54 were calculated by using the Z expansion method. Relativistic effects are taken into account using the Breit–Pauli operators. The asymptotic dependence on n of the energy matrix is discussed for 2lnl' states. Intermediate coupling coefficients obtained after diagonalizing the energy matrices were also studied. It was observed that these coefficients change very rapidly with n and Z due to a redistribution of contribution between relativistic and correlation effects. As a result, all other atomic characteristics (radiative and nonradiative transition probabilities, branching ratios) display non-monotonous Z- and n-dependences with maxima and minima.

Ejected electrons from the singlet and triplet states of doubly excited and ions, produced by 25, 50, 75 and 100 keV and Ar collisions have been measured with high-resolution electron spectroscopy. Only singlet states were observed when the target was He; in contrast, many triplet states were observed in and Ar collisions. Both singlet and triplet states contributed to the electron spectra in collisions, in particular, triplet states were conspicuous at low energy. Two theoretical methods, perturbation theory or Z expansion (MZ code) and multiconfigurational Hartree-Fock (Cowan code) were used for identification of ejected-electron spectra. The collision energy dependence of the spectra is discussed.

Energies of the 2s2(1S)3l, 2s2p(1P)3l, 2s2p(3P)3l, 2p2(3P)3l, 2p2(1D)3l, and 2p2(1S)3l states, withl = s,p, andd, for B-like ions with nuclear chargesZin the range 6–30 are determined to second order in relativistic many-body perturbation theory starting from a frozen-core Dirac–Fock basis. These perturbation theory calculations include the first- and second-order diagram contributions from the Coulomb and Breit operators for diagonal and nondiagonal matrix elements. Corrections for the frequency dependence of the Breit interaction are taken into account in lowest order. The Lamb-shift correction to the energies is also included in lowest order. Contributions of the three-electron interaction are compared with contributions of the one- and two-electron interactions. Comparisons are made with other theoretical calculations and with experimental data. We obtain excellent agreement for term splitting, even for low-Zions.

The dielectronic recombination rate coefficients to the excited states for n = 2-6 are calculated including - states. The values for the excited states higher than n = 6 are extrapolated and the total dielectronic recombination rate coefficients are derived.

The excitation energies and the probabilities for radiative and radiationless decays of hollow atom states belonging to the 2s22p, 2s2p2 and 2p3 configurations have been calculated on the basis of perturbation theory method (1/Z-expansion) in a broad range of values of atomic number Z. Our results agree well with the first observation of these states and the theoretical and experimental results obtained recently for neutral Li atoms. It should be noted that the 1/Z expansion method gives more accurate results for ions than for neutral systems, because of the limited number of coefficients of 1/Z expansion calculated in this work. In this case the good agreement provided by our results for neutral system allows us to believe that our data for the same triply excited states with Z>3 should be used for prediction of new experiments with these states.

Energy levels, radiative transition probabilities and autoionization rates for CuXIX including the 1s22s22p53lnl' (n = 3 ÷ 8, l' ≤ n – 1) and 1s22s2p63lnl' (n = 3 ÷ 4, l' ≤ n – 1) doubly excited states were calculated using the multi-configurational Hartree–Fock method (Cowan code). Contributions of relativistic effects were discussed in comparison with data obtained by the multi-configurational Dirac–Fock method (YODA code). Application of the theoretical data for interpretation of experimental spectra obtained by double-electron capture in slow ion-atom collisions is discussed.

Single and double electron capture processes by O 6+ from He at 90 keV have been investigated by observation of the emission spectrum in the wavelength region of 290–510 nm. In addition to transitions from excited states of O 5+ populated by single electron capture processes, Yrast transitions from Rydberg states (1s 2 2s n l ) of O 4+ populated by double electron capture have been observed. Transfer target excitation processes have been confirmed by the observation of transitions from excited states of He + .

Theoretical atomic data from the MZ code with the Z expansion method by Safronova, the AUTOLSJ code using a statistical model potential by Cornille, and the YODA code derived from the MCDF approximation by Nilsen for the wavelengths and intensities of the dielectronic and inner shell satellite lines of He- to C-like Fe and Li-like Ca and S ions are compared in the form of synthetic spectra. The agreement is rather good, being within 20% for the main satellite lines. As an example of the application of the data we analyze the spectrum of Fe XXV from a solar flare obtained by the Yohkoh space vehicle.

Energies of the low-lying excited states of six atomic systems with two electrons above the core (Mg I, Al II, Hg I, Tl II, Pb I, and Bi II) and three systems with three electrons above the core (Al I, Tl I, and Bi I) are determined to second order in relativistic many-body perturbation theory using frozen-core Dirac-Hartree-Fock orbitals as a basis set. In the present report, the Breit interaction is included to first order only. Diagonalization of the effective Hamiltonian is carried out using two methods: (I) the symmetric first-order Hamiltonian (including both Coulomb and Breit interactions) is diagonalized and then the second-order correlation is determined using the first-order eigenvectors; (II) the first-order (Coulomb plus Breit) together with the non-symmetric second-order effective Hamiltonian is diagonalized. Different model spaces are considered. Contributions from the three-electron interaction are compared with contributions from the two- and one-electron interactions. Comparisons with experiment are made.

Energy levels, radiative transition probabilities and autoionization rates for CIII including 1s22pnl′ [n = 2–6, l′ ≤ (n − 1)] and 1s23lnl′ [n = 3–6, l′ ≤ (n − 1)] states were calculated by using the multi-configurational Hartree-Fock method (Cowan code). Autoionizing levels above the 1s22s and 1s22p thresholds were considered and their contributions were computed. Branching ratios on the autoionization rate to the first threshold and intensity factors were calculated for satellite lines of the CIII ion. The dielectronic recombination rate coefficients to the excited states for n = 2–6 were calculated. The values for the excited states higher than n = 6 were extrapolated and the total dielectronic recombination rate coefficients were derived. The rate coefficients to the excited states were fitted to an analytical formula and the fit parameters are given.

Energies of the 2s3s (), 2s3p (), 2s3d (), 2p3s (), 2p3p () and 2p3d () states for Be-like ions with nuclear charges Z in the range 4 - 30 and for Z = 54 are determined to second order in relativistic many-body perturbation theory starting from a frozen-core Dirac - Fock basis. Second-order Coulomb and second-order Breit - Coulomb correlation energies are evaluated. Corrections for the frequency dependence of the Breit interaction are taken into account in lowest order. Lamb-shift corrections to the energies are also included in lowest order. Comparisons are made with other theoretical calculations and with experimental data. We obtain an excellent agreement with experiment for term splitting, even for low-Z ions. Results for the 2p - 3d excitation energies for are also in very good agreement with experiment.

The dielectronic recombination rate coefficients to the excited states for n = 2–6 are calculated including 1s22l2l'nl'' (n = 2–6, l'' ≤ (n − 1)). The values for the excited states higher than n = 6 are extrapolated and the total dielectronic recombination rate coefficients are derived. The rate coefficients to the excited states are fitted to an analytical formula and the fit parameters are given. The effective recombination rate coefficient for different electron densities are also derived.