QED effects in Cu-like Pb recombination resonances near threshold

In an electron-ion recombination study with Pb53+ dielectronic recombination resonances are found for as low as approximately 10(-3)-10(-4) eV relative energy. The resonances have been calculated by relativistic many-body perturbation theory and through comparison with experiment the Pb53+(4p(1/2)-4s(1/2)) energy splitting of approximately 118 eV is determined with an accuracy comparable to the position of the first few resonances, i.e., approximately 10(-3) eV. Such a precision provides a test of QED in a many-body environment at a level which can still not be reached in calculations.     

Calculation of dielectronic recombination cross sections and rate coefficients for heliumlike carbon

A simplified relativistic configuration interaction method is used to calculate the dielectronic recombination cross sections and rate coefficients for heliumlike carbon. In this method, the infinite resonant doubly excited states can be treated conveniently in the frame of Quantum Defect Theory. Our calculated cross sections are in agreements with the experimental measurements except for the 1s2lnl'(n=6,7) resonances. The total energy-integrated cross sections and rate coefficients over all dielectronic resonances are in agreements with the experimental measurements within percent. Received: 7 July 1997 / Revised: 7 October 1997 / Accepted: 8 December 1997     

Dielectronic recombination of Li-like neon and argon

We have measured dielectronic recombination rates and energies for n=0 transitions of Ne⁷⁺ and Ar¹⁵⁺ beams stored in CRYRING. The energy resolution was in the order of 10^–2 eV FWHM; the absolute accuracy in the position of the resonances is in the same order. The energy positions of the dielectronic recombination resonances are compared to theoretical calculations of the fine-structure splittings.     

离子和冷却电子重组的高分辨谱研究(英文)

给出了在CRYRING重离子储存环上测量到的在很低能量下电子与离子重组的最新实验结果和有关速率系数增强的新的数据 .主要讨论类锂、类钠和类铜离子的共振双电子重组的新近测量结果 ,以及从这些共振谱中所导出的非常精确的离子能级劈裂值 ,从而将严格检验相对论效应、电子关联效应和量子电动力学效应 .其中 ,对类锂Kr3 3 + 离子 2s1/2 能级Lamb移位的确定精度达到了0 .1%. We present our latest results on recombination of electrons with ions at very low energies obtained at the CRYRING heavy-ion storage ring. New data on the enhanced rate coefficient are shown. Then we concentrate on recent measurements of dielectronic recombination resonances with Li-like, Na-like, and Cu-like ions, where from the spectra of resonances very accurate values for energy splittings are derived for crucial tests of relativistic, correlation, and QED effects.     

Measurement of the KLL Dielectronic Recombination Resonances in He-like to C-like Kr Ions

The KLL dielectronic recombination processes of highly charged He-like to C-like Kr ions have been studied experimentally. The measurement was performed on the newly developed Shanghai electron beam ion trap （Shanghai-EBIT） facility. Characteristic x-rays from both dielectronic recombination and radiative recombination are detected as the electron beam energy is scanned through the resonances. The KLL resonant strengths obtained are 5.41×10^-19, 4.33×10^-19, 3.59×10^-19, 2.05×10^-19 and 0.98×10^-19 cm^2 eV for He-like to C-like Kr ions, respectively.     

Hybrid forms of beat phenomena in nuclear forward scattering of synchrotron radiation

In nuclear forward scattering (NFS) of synchrotron radiation, inter-resonance interference leads to a quantum beat (QB), and intra-resonance interference to a dynamical beat (DB). In general both interference processes determine the time evolution of NFS. Only in the case of far distant resonances the resulting interference pattern can be interpreted as a well distinguishable combination of QB and DB. Multiple scattering by near neighbouring resonances, by contrast, leads to a hybridisation of QB and DB. In particular, asymmetrical continuous distributions of resonances make QB and DB blend into a fast hybrid beat with thickness dependent period and distribution sensitive modulation.

     

Overlapping identical resonances and double radiative interference effects in recombination of heavy multicharged ions

The purely QED effect of double radiative interference in the recombination of electrons with heavy multicharged ions is discussed. Numerical calculations of the corresponding cross sections in the vicinities of the KL ₁₂ M ₁₂ and KM ₁₂ M ₁₂ dielectronic recombination resonances of heliumlike uranium are reported. The possibility of near-future experimental observation of the effect with the Super-EBIT facility is suggested. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 552–556 (10 October 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Progress in stored ion beam experiments on atomic and molecular processes

Stored fast ion beams in atomic and molecular collision experiments are discussed with an emphasis on electron–ion interactions at low relative energies. Recent progress was obtained in electron collision spectroscopy using an electron-cooled stored ion beam and a separate electron target in the same storage ring; from a cryogenic photocathode, electron beams with internal temperatures of 5 to 10 K were produced. Results are presented for dielectronic recombination resonances, resolving the hyperfine structure of stored lithiumlike scandium ions and obtaining precise results for the fine structure splitting of these ions, and for ro-vibrational resonances in the recombination of electrons with hydrogen molecular ions, revealing sharp structures down to 2 meV. An overview of the cryogenic storage ring (CSR) project in Heidelberg is given.     

Enhancement of Dielectronic Recombination by External Electromagnetic Fields

The enhancement of the dielectronic recombination rate of lithiumlike Ne⁷⁺ and O⁵⁺ ions by external electromagnetic fields has been measured at the storage ring CRYRING. The energy range covered all 1s ²2pnl dielectronic recombination resonances attached to the 2s→2p core excitation. Electric fields up to 1436 V/cm were applied in the Ne⁷⁺ experiment and the saturation of the enhancement with increasing electric field could clearly be seen. In the O⁵⁺ experiment the enhancement was studied as a function of the Rydberg quantum number n.

     

Observation of trielectronic recombination in Be-like Cl ions

Recombination involving the core excitation of two electrons, which may be termed trielectronic recombination, has been experimentally identified for the first time. Using Cl13+ ions circulating in the TSR heavy-ion storage ring, we have observed surprisingly strong low-energy trielectronic recombination resonances, comparable to the dielectronic process. At higher electron-ion collision energies, trielectronic recombination is suppressed due to the autoionization of the triply excited intermediate state into excited final states. The formation of the intermediate state depends sensitively on configuration mixing, making trielectronic recombination a challenge to atomic-structure calculations.     

Efficient field-free orientation of CO molecules using a three-step excitation scheme

We report results from detailed state selective photo-recombination study along with the doubly excited autoionizing resonances in Be-like C²⁺ and Al⁹⁺ ions. In the present investigation, the primary focus is on detailed energy profiles of the individual photo-recombination cross sections. The calculation was carried out for the excited Rydberg states of type 1s ²2sns(¹S^e) which interact with the odd-parity continua up to the C³⁺ and Al¹⁰⁺ 2p threshold limit. The numerical evaluation has been performed at a fine energy mesh across all the autoionizing Rydberg series of resonances 1s ²2pns(¹P⁰) converging to Li-like ion 2p threshold. The method of calculation keeps the essential ingredients of the Feshbach projection operator approximation. The photo-ionization cross sections have been evaluated with and without relativistic effects included into the R-matrix numerical procedures, while the allowance for both quantum interference between dielectronic and radiative recombination, and overlapping resonances has been done utilizing results from the earlier R-matrix Floquet calculation. We discuss all these results with respect to the effect of quantum interference term on the energy dependence profile of photo-recombination cross section for studied transitions.     

Statistical dielectronic recombination rates for multielectron ions in plasma

We describe the general analytic derivation of the dielectronic recombination (DR) rate coefficient for multielectron ions in a plasma based on the statistical theory of an atom in terms of the spatial distribution of the atomic electron density. The dielectronic recombination rates for complex multielectron tungsten ions are calculated numerically in a wide range of variation of the plasma temperature, which is important for modern nuclear fusion studies. The results of statistical theory are compared with the data obtained using level-by-level codes ADPAK, FAC, HULLAC, and experimental results. We consider different statistical DR models based on the Thomas–Fermi distribution, viz., integral and differential with respect to the orbital angular momenta of the ion core and the trapped electron, as well as the Rost model, which is an analog of the Frank–Condon model as applied to atomic structures. In view of its universality and relative simplicity, the statistical approach can be used for obtaining express estimates of the dielectronic recombination rate coefficients in complex calculations of the parameters of the thermonuclear plasmas. The application of statistical methods also provides information for the dielectronic recombination rates with much smaller computer time expenditures as compared to available level-by-level codes.     

A theory of intermediate structure,overlapping resonances and photonuclear reactions in light nuclei

Starting from a many body Hamiltonian a general theory involving intermediate structures and overlapping resonances in nuclear reaction has been worked out. This treatment, based on Trefftz's work on dielectronic recombination in atomic physics, avoids explicit use of projection operators and all relevant quantities like decay widths and energy shifts are explicitly expressed in terms of two body matrix elements. In particular, attention has been focused on the interaction of bound states among themselves and then on the coupling of the continuum with these interacting bound states. For the case of overlapping resonances, it is shown that in general one cannot take a simple energy average of the resonant amplitudes, and explicit equations for this case have been obtained. This microscopic theory also provides a justification of the model of Duke, Malik, and Firk in explaining the intermediate structure in giant dipole resonance region of ¹⁶O and ²⁸Si. However, the formalism is a general one and is suitable for the study of intermediate structure involving isolated and overlapping resonances for many types of reactions.     

Resonant enhancement of dielectronic recombination by a microwave field

We have observed dielectronic recombination of Ba+ and e(-) from a continuum of finite bandwidth in the presence of microwave fields of frequencies 8.08 and 12.05 GHz and amplitudes of up to 2 V/cm. There are sharp resonant enhancements when the microwave frequency matches the Deltan = 1, 2, and 3 resonances of the intermediate autoionizing Rydberg states, and we attribute the enhancements to resonant microwave Stark l mixing. The microwave field provides a simple and powerful way to enhance the recombination rate for incident electrons of a specific energy.     

Cross-molecular coupling in combined photoassociation and Feshbach resonances

We model combined photoassociation and Feshbach resonances in a Bose-Einstein condensate. When the magnetic field is far-off resonance, cross coupling between the two target molecules--enabled by the shared dissociation continuum--leads to an anomalous dispersive shift in the position of laser resonance, as well as unprecedented elimination and enhancement of resonant photoassociation via quantum interference. For off-resonant lasers, a dispersive shift and quantum interference appear similarly in resonant three-body Feshbach losses, except that the Feshbach node is tunable with intensity.     

Deep-core dielectronic-capture resonances in the electron-impact ionization of heavy atomic ions

Experimental measurements and theoretical calculations are carried out for the electron-impact ionization of Sm(12+). The low energy region of the single ionization cross section for Sm(12+) is found to be dominated by contributions from the indirect process of excitation autoionization. At about 1.0 keV strong resonance features are found in the experimental crossed-beam measurements performed in scan mode at high resolution. Theoretical calculations confirm that the high energy experimental features are due to deep-core dielectronic capture followed by sequential double Auger decay. The discovery of these unusual high energy resonances in single and multiple ionization opens the door for future systematic studies of how heavy atomic ions with deep inner-shell vacancies achieve final stabilization.     

Isotope shifts of dielectronic resonances for heavy few-electron ions

Effects of the nuclear charge distribution upon the total cross-section of dielectronic recombination are investigated. We calculated isotope shifts of resonance energies for H-, He- and Li-like heavy ions in the relativistic domain from Z = 54 to Z = 94. We point out that the position of the resonances is most influenced in KLL transitions in very heavy elements and their shifts are most likely to be measurable for systems with intra-shell transitions. For these systems, dielectronic recombination experiments provide a new method to determine the parameters of the nuclear charge distribution.Received: 26 July 2004, Published online: 5 October 2004PACS: 34.80.Lx Electron-ion recombination and electron attachment - 31.30.Jv Relativistic and quantum electrodynamic effects in atoms and moleculesR. chiopu: Now at Institut für Physik, Johannes-Gutenberg-Universität, Mainz, Germany.     

Recombination of Sc3+ ions with free electrons

Recombination of Ar-like Sc³⁺ ions has been studied experimentally at the TSR for center of mass energies ranging from approximately 12–18 eV. In this energy range rather broad resonances from short lived Sc²⁺(3s²3p⁵3d^{2 2}F) intermediate states are expected. For these resonances recent theoretical work predicts strongly asymmetric lineshapes due to quantum mechanical interferences between radiative and dielectronic recombination channels. The study of this heavy, low-charged ion suffered from a high background due to electron capture and the outcome of our experiment does not yet allow for a conclusive test of the theoretical predictions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of dielectronic recombination excitation in the solar x-ray lines of calcium-ions

The effect of dielectronic recombination as an excitation process in the intensity of solar x-ray lines of calcium ions is investigated. It is found that x-ray line intensities are enhanced by 15% to 88% with the inclusion of dielectronic recombination as an excitation mechanism.     

Dielectronic resonance method for measuring isotope shifts

Long standing problems in the comparison of very accurate hyperfine-shift measurements to theory were partly overcome by precise measurements on few-electron highly charged ions. Still the agreement between theory and experiment is unsatisfactory. In this Letter, we present a radically new way of precisely measuring hyperfine shifts, and demonstrate its effectiveness in the case of the hyperfine shift of 4s1/2 and 4p1/2 in 207Pb53+. It is based on the precise detection of dielectronic resonances that occur in electron-ion recombination at very low energy. This allows us to determine the hyperfine constant to around 0.6 meV accuracy which is on the order of 10%.