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N. Nahar - One of the best experts on this subject based on the ideXlab platform.
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Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. VIII. Ar XIII with New Features
Astrophysical Journal Supplement Series, 2020Co-Authors: N. NaharAbstract:Ar xiii is found to be unique with new features in Electron-Ion Recombination not seen in any other ion. The ion has been studied with the unified method, which provides a theoretically self-consistent set of atomic parameters for the inverse processes of photoionization and total Electron-Ion Recombination. Unified method subsumes both the radiative Recombination (RR) and dielectronic Recombination (DR) within the framework of close-coupling formulations using the R-matrix method. A set of four DR ‘‘bumps,’’ two in the low-temperature and two in the high-temperature regions, is found to exist in the Recombination rates of Ar xiv þ e ! Ar xiii. This is in contrast to two typical DR ‘‘bumps,’’ one at high temperature common for most ions and one at low temperature depending on the presence of near threshold autoionizing resonances in the bound-free process. Large-scale ab initio calculations have been carried out for photoionization and Electron-Ion Recombination cross sections of Ar xiii. The ion is represented by a large close-coupling eigenfunction expansion of 37 core Ar xiv states from n ¼ 2 and 3 complexes. This enables core excitations of type n ¼ 0 and 1. The n ¼ 1 transitions have much higher radiative decay rates than those of n ¼ 0 and cause the fourth DR bump around 2 ;10 6 K. For a large number of bound states, Ar xiii exhibits more extensive resonant structures and wider PEC (photoexitation-of-core) resonances for n ¼ 3 core states than those of n ¼ 2 states. Hence, the high-energy regions of photoionization and Recombination are dominated by these structures. A total of 684 bound states with valence electron n � 10 and l � 9 are found for Ar xiii. Total and partial photoionization cross sections of all bound states, state-specific Recombination rates of 561 bound states, and total Recombination rate coefficients at a large temperature range are presented for Ar xiii. Subject headingg atomic data — atomic processes
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Photoionization and Electron-Ion Recombination of Cr I
New Astronomy, 2009Co-Authors: N. NaharAbstract:Abstract Results from the unified method for photoionization and electron–ion Recombination of ( He I + h ν ↔ He II + e ) are presented. He I wave function is represented by an expansion that includes 10 core states for excitations to n = 2, 3, and 4 states. A total of 99 bound LS states with n ⩽ 10 are obtained. They all, except two, agree with the observed energies in less than 1%. Photoionization cross sections σ PI for the total ionization, leaving the residual ion in all excited states, and the partial ionization, leaving the ion in the ground state, are presented for all 99 bound states. Calculated σ PI agree very well with the measured ground state cross section. Detailed resonant features of σ PI and coupling effects on the background cross sections are illustrated. For the Recombination process, state-specific and total Recombination rate coefficients are presented. These include both the radiative and dielectronic Recombination processes. In addition, the total Recombination spectrum with electron energy is presented and exhibits the resonant features that were observed experimentally. Recombination rates for hydrogenic He II is also presented. The present results obtained in LS coupling approximation provide a unified and self-consistent sets of results for astrophysical modelings of the two inverse radiative processes until highly accurate and precise results will be available through comprehensive relativistic calculations.
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The Iron Project and the Rmax Project: Photoionization, Electron-Ion Recombination of Fe XVII and oscillator strengths for Fe XXII
Journal of Physics: Conference Series, 2009Co-Authors: Anil K. Pradhan, N. Nahar, Werner EissnerAbstract:The Iron Project and the Rmax Project aim in detail study of radiative and collisional processes of astrophysically abundant iron and iron-peak elements over a wide energy range from infra-red to X-rays. We will illustrate new features of high energy photoionization and high temperature Electron-Ion Recombination of Fe XVII that are more prominent than the low energy and low temperature. We have noted that core excitations to high lying levels introduce much stronger, high peak resonances than those to the low lying ones. We also report an extensive set of radiative transitions for Fe XXII. Oscillator strengths, line strengths, lifetimes and radiative decay rates for E1 transitions will be presented for 771 fine structure levels with 1/2 ≤ J ≤ 17/2. The parameters for a large set of forbidden E2, E3, M1, M2 transitions will also be presented.
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Electron-Ion Recombination and photoionization of Fe XXI
Journal of Quantitative Spectroscopy & Radiative Transfer, 2008Co-Authors: N. NaharAbstract:Abstract Results for electron–ion Recombination and photoionization of ( Fe XXI + h ν ↔ Fe XXII + e ) , with emphasis in high-temperature region, are presented from ab initio unified method. The unified method, based on close coupling (CC) approximation and R-matrix method, (i) subsumes both the radiative Recombination (RR) and dielectronic Recombination (DR), (ii) enables self-consistent sets of photoionization and Recombination cross sections from using an identical wavefunction for both the processes, and (iii) provides state-specific Recombination rates of a large number of bound states. A large CC wavefunction expansion, which includes the ground and 28 core excitations of n = 2 and 3 complexes and span a wide energy range, has been used. Compared to Δ n = 2 – 2 , Δ n = 2 – 3 core excitations are found to introduce strong resonant structures and enhance the background photoionization cross sections ( σ PI ) in the high-energy region. These features along with prominent photoexcitation-of-core (PEC) resonances at n = 3 core thresholds have increased the unified total Recombination rate coefficients ( α R ( T ) ) at temperatures T > 10 6 K , region of maximum abundance of the ion in collisional equilibrium, by a factor of 1.6 over previous calculations. State-specific Recombination rate coefficients α R ( nLS ) , which include both the RR and DR, are presented for the first time for 685 bound states with n ⩽ 10 and l ⩽ 9 . The unified total Recombination rate with photoelectron energy α R ( E ) is presented and the role of low-energy near-threshold fine structure resonances is illustrated. The present results should provide a reasonably complete self-consistent set of Recombination rates and photoionization cross sections for astrophysical modelings of high-temperature plasmas from optical to far-ultraviolet wavelength regions.
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Self-consistent R-matrix approach to photoionization and unified Electron-Ion Recombination
Radiation Physics and Chemistry, 2004Co-Authors: N. Nahar, Anil K. PradhanAbstract:Abstract A unified scheme using the R-matrix method has been developed for electron–ion Recombination subsuming heretofore separate treatments of radiative and dielectronic Recombination (RR and DR). The ab initio approach within the coupled channel approximation has several inherent advantages in addition to the natural unification of resonant and non-resonant phenomena. It enables a general and self-consistent treatment of photoionization and electron–ion Recombination employing identical wavefunction expansion. Detailed balance takes account of interference effects due to resonances in cross sections, calculated explicitly for a large number of recombined (e+ion) bound levels over extended energy regions. The theory of DR by Bell and Seaton is adapted for high- n resonances in the region below series limits. The R-matrix method is employed for (A) partial and total photoionization and photoRecombination cross sections of (e+ion) bound levels, and (B) DR and (e+ion) scattering cross sections. Relativistic effects and fine structure are considered in the Breit–Pauli approximation. Effects such as radiation damping may be taken into account where necessary. Unified Recombination cross sections are in excellent agreement with measurements on ion storage rings to about 10–20%. In addition to high accuracy, the strengths of the method are: (I) both total and level-specific cross sections and rate coefficients are obtained, and (II) a single (e+ion) Recombination rate coefficient for any given atom or ion is obtained over the entire temperature range of practical importance in laboratory and astrophysical plasmas, (III) self-consistent results are obtained for the inverse processes of photoionization and Recombination; comprehensive datasets have been computed for over 50 atoms and ions. Selected data are presented for iron ions.
Joachim Burgdörfer - One of the best experts on this subject based on the ideXlab platform.
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Enhanced Electron-Ion Recombination in ion storage rings
Hyperfine Interactions, 2020Co-Authors: Maria Hörndl, Shuhei Yoshida, Joachim Burgdörfer, Gerald Gwinner, Andreas WolfAbstract:We review recent advances in the understanding of the enhanced electron–ion Recombination observed in storage ring experiments. The measured Recombination rates show a strong enhancement relative to what the standard radiative Recombination rates predict. A transient motional electric field is induced in the merging region of an electron and an ion beam in the electron cooler. This induced field opens an additional pathway for free-bound transitions of electrons. The formed Rydberg states can be radiatively stabilized and contribute to the measured rate. We show that this “field induced Recombination” (FIR) explains the gap previously observed between measurements and the standard radiative Recombination rate.
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Classical dynamics of enhanced low-energy Electron-Ion Recombination in storage rings
Physical Review A, 2006Co-Authors: Maria Hörndl, Shuhei Yoshida, Gerald Gwinner, Andreas Wolf, Marek Seliger, Joachim BurgdörferAbstract:Electron-Ion Recombination observed in storage ring experiments shows a strong enhancement of the Recombination rate for highly charged ions with low-energy electrons relative to what standard radiative Recombination rates predict. We present detailed simulations of the toroid and solenoid regions of the electron cooler, analyzing the classical dynamics of an electron in the presence of the Coulomb field of the ion, the homogeneous magnetic field inside the cooler, and the transient electric field in the merging section. Both bound and continuum electron dynamics display partially chaotic motion. For bound states we observe stochastic and quasiperiodic l mixing while for continuum electrons we find transient chaos characterized by a fractal generalized reflection function. We determine the modified radiative and field-induced Recombination of the electron with a highly charged ion in a storage ring. The obtained absolute excess Recombination rates are compared with the experimental data and, overall, reasonable agreement is found. The scaling of the rate with the average relative energy, the ion charge, the magnetic guiding field, and the electron-beam temperatures is analyzed.
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Enhancement of low energy Electron-Ion Recombination in a magnetic field: influence of transient field effects
Physical Review Letters, 2005Co-Authors: Maria Hörndl, Shuhei Yoshida, Gerald Gwinner, Andreas Wolf, Joachim BurgdörferAbstract:Electron-Ion Recombination observed in storage ring experiments shows a strong enhancement relative to what standard radiative Recombination rates predict. We simulate the effect of a transient motional electric field induced by the merging of an electron and an ion beam in the electron cooler which opens an additional pathway for free-bound transitions of electrons. We show that the measured rate contains a significant contribution from radiative stabilization of Rydberg states formed by this transient motional electric field. The absolute excess Recombination rates obtained are in good agreement with the experimental data. The scaling of the rate with the ion charge and the magnetic guiding field is analyzed.
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Enhancement of low energy electron–ion Recombination in a magnetic field: Influence of transient field effects
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005Co-Authors: Maria Hörndl, Shuhei Yoshida, Károly Tőkési, Joachim BurgdörferAbstract:Abstract The experimentally observed enhancement of electron–ion Recombination at low relative energies is still a widely open problem. During the merging of an electron and an ion beam in the electron cooler of the storage ring a transient motional electric field is present in the rest frame of the ion which, in turn, may open an additional pathway for free–bound transitions of electrons. We present simulations performed for the toroidal merging geometry of the TSR in Heidelberg. Very high Rydberg states, typically n ⩾ 400, are found to be populated during the merging process. Radiative stabilization of these Rydberg states inside the solenoid can contribute to the observed enhancement.
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Enhancement of Low-Energy Electron Ion Recombination in a Magnetic Field
Hyperfine Interactions, 2003Co-Authors: Maria Hörndl, Shuhei Yoshida, Karoly Tökési, Joachim BurgdörferAbstract:Electron–ion Recombination in cold magnetized plasmas shows a dramatic enhancement of the radiative Recombination rate for bare highly charged ions relative to what standard radiative Recombination rates predict. To understand the mechanism of this enhancement we investigate the classical chaotic dynamics of an electron in the combined Coulomb field of the ion and the magnetic field in the electron cooler. An increased flux of electrons visiting the vicinity of the target ion leads to an enhancement of the Recombination process.
Mariusz Wojcik - One of the best experts on this subject based on the ideXlab platform.
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Electron–ion Recombination in radiation tracks in liquid argon: a computer simulation study
Research on Chemical Intermediates, 2020Co-Authors: Michal Jaskolski, Mariusz WojcikAbstract:A simulation method is proposed to model electron–ion Recombination in radiation tracks in liquid argon at 87 K. The method is applied to calculate the electron escape probability in clusters of up to 20 pairs of electrons and cations that represent a fragment of the track. The results reproduce the basic features of the track Recombination in liquid argon observed in experiment.
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Electron–ion Recombination in nuclear recoils tracks in nonpolar liquids. Calculation of the effect of external electric field on the escape probability
Radiation Physics and Chemistry, 2016Co-Authors: Piotr Mateja, Mariusz WojcikAbstract:Abstract A computer simulation method is applied to study electron–ion Recombination in tracks of low-energy nuclear recoils in nonpolar liquids in which the electron transport can be described as ideal diffusion. The electron escape probability is calculated as a function of applied electric field, both for the field parallel to the track and for the field perpendicular to the track. The dependence of escape probability on the field direction is the stronger, the longer the ionization track, with a significant effect being found already for tracks of ~100 nm length. The results are discussed in the context of possible applications of nonpolar molecular liquids as target media in directional dark matter detectors.
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Electron-Ion Recombination in dense gaseous and liquid argon: effects due to argon cation clusters allow to explain the experimental data
Chemical Physics Letters, 2004Co-Authors: Mariusz Wojcik, Masanori TachiyaAbstract:The role of cation clusters in the bulk Electron-Ion Recombination in dense gaseous and liquid argon is investigated. The size and structure of cation clusters in those systems are determined by a Monte Carlo simulation. Then, the rate constants of Electron-Ion Recombination are calculated by another simulation method that takes into account the presence of cation clusters in the considered systems. A good agreement with experiment for both dense gaseous and liquid argon is obtained.
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Electron thermalization and electron–ion Recombination in liquid argon
Chemical Physics Letters, 2003Co-Authors: Mariusz Wojcik, Masanori TachiyaAbstract:Abstract The processes of electron thermalization and geminate electron–ion Recombination in liquid argon at 87 K are studied by computer simulations based on the Cohen–Lekner theory of electron transport in liquids. The mean thermalization time of 1.8 ns is obtained, which is in agreement with experiment, and the mean thermalization distance is calculated as 2600 nm with the standard deviation of 1100 nm. The probability of geminate Recombination is found to be very low (∼10 −3 ).
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Electron transport and electron–ion Recombination in liquid argon: simulation based on the Cohen–Lekner theory
Chemical Physics Letters, 2002Co-Authors: Mariusz Wojcik, Masanori TachiyaAbstract:Abstract A simulation method is proposed to model the electron motion in liquid argon. The method is based on the Cohen–Lekner theory of hot electrons in liquids, and takes account of different rates of energy and momentum transfers in electron collisions. The simulation method is applied in the calculations of the electron mobility and the electron–ion Recombination rate constant in liquid argon at 87 K. Agreement between the simulation results and experiment is satisfactory.
Maria Hörndl - One of the best experts on this subject based on the ideXlab platform.
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Enhanced Electron-Ion Recombination in ion storage rings
Hyperfine Interactions, 2020Co-Authors: Maria Hörndl, Shuhei Yoshida, Joachim Burgdörfer, Gerald Gwinner, Andreas WolfAbstract:We review recent advances in the understanding of the enhanced electron–ion Recombination observed in storage ring experiments. The measured Recombination rates show a strong enhancement relative to what the standard radiative Recombination rates predict. A transient motional electric field is induced in the merging region of an electron and an ion beam in the electron cooler. This induced field opens an additional pathway for free-bound transitions of electrons. The formed Rydberg states can be radiatively stabilized and contribute to the measured rate. We show that this “field induced Recombination” (FIR) explains the gap previously observed between measurements and the standard radiative Recombination rate.
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Classical dynamics of enhanced low-energy Electron-Ion Recombination in storage rings
Physical Review A, 2006Co-Authors: Maria Hörndl, Shuhei Yoshida, Gerald Gwinner, Andreas Wolf, Marek Seliger, Joachim BurgdörferAbstract:Electron-Ion Recombination observed in storage ring experiments shows a strong enhancement of the Recombination rate for highly charged ions with low-energy electrons relative to what standard radiative Recombination rates predict. We present detailed simulations of the toroid and solenoid regions of the electron cooler, analyzing the classical dynamics of an electron in the presence of the Coulomb field of the ion, the homogeneous magnetic field inside the cooler, and the transient electric field in the merging section. Both bound and continuum electron dynamics display partially chaotic motion. For bound states we observe stochastic and quasiperiodic l mixing while for continuum electrons we find transient chaos characterized by a fractal generalized reflection function. We determine the modified radiative and field-induced Recombination of the electron with a highly charged ion in a storage ring. The obtained absolute excess Recombination rates are compared with the experimental data and, overall, reasonable agreement is found. The scaling of the rate with the average relative energy, the ion charge, the magnetic guiding field, and the electron-beam temperatures is analyzed.
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Enhancement of low energy Electron-Ion Recombination in a magnetic field: influence of transient field effects
Physical Review Letters, 2005Co-Authors: Maria Hörndl, Shuhei Yoshida, Gerald Gwinner, Andreas Wolf, Joachim BurgdörferAbstract:Electron-Ion Recombination observed in storage ring experiments shows a strong enhancement relative to what standard radiative Recombination rates predict. We simulate the effect of a transient motional electric field induced by the merging of an electron and an ion beam in the electron cooler which opens an additional pathway for free-bound transitions of electrons. We show that the measured rate contains a significant contribution from radiative stabilization of Rydberg states formed by this transient motional electric field. The absolute excess Recombination rates obtained are in good agreement with the experimental data. The scaling of the rate with the ion charge and the magnetic guiding field is analyzed.
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Enhancement of low energy electron–ion Recombination in a magnetic field: Influence of transient field effects
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005Co-Authors: Maria Hörndl, Shuhei Yoshida, Károly Tőkési, Joachim BurgdörferAbstract:Abstract The experimentally observed enhancement of electron–ion Recombination at low relative energies is still a widely open problem. During the merging of an electron and an ion beam in the electron cooler of the storage ring a transient motional electric field is present in the rest frame of the ion which, in turn, may open an additional pathway for free–bound transitions of electrons. We present simulations performed for the toroidal merging geometry of the TSR in Heidelberg. Very high Rydberg states, typically n ⩾ 400, are found to be populated during the merging process. Radiative stabilization of these Rydberg states inside the solenoid can contribute to the observed enhancement.
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Enhancement of Low-Energy Electron Ion Recombination in a Magnetic Field
Hyperfine Interactions, 2003Co-Authors: Maria Hörndl, Shuhei Yoshida, Karoly Tökési, Joachim BurgdörferAbstract:Electron–ion Recombination in cold magnetized plasmas shows a dramatic enhancement of the radiative Recombination rate for bare highly charged ions relative to what standard radiative Recombination rates predict. To understand the mechanism of this enhancement we investigate the classical chaotic dynamics of an electron in the combined Coulomb field of the ion and the magnetic field in the electron cooler. An increased flux of electrons visiting the vicinity of the target ion leads to an enhancement of the Recombination process.
Anil K. Pradhan - One of the best experts on this subject based on the ideXlab platform.
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Self-consistent R-matrix approach to photoionization and unified electron–ion Recombination
Radiation Physics and Chemistry, 2020Co-Authors: Sultana N. Nahar, Anil K. PradhanAbstract:A unified scheme using the R-matrix method has been developed for Electron-Ion Recombination subsuming heretofore separate treatments of radiative and dielectronic Recombination (RR and DR). The ab initio coupled channel approach unifies resonant and non-resonant phenomena, and enables a general and self-consistent treatment of photoionization and Electron-Ion Recombination employing idential wavefunction expansion. Detailed balance takes account of interference effects due to resonances in cross sections, calculated explicitly for a large number of recombined (e+ion) bound levels over extended energy regions. The theory of DR by Bell and Seaton is adapted for high-n resonances in the region below series limits. The R-matrix method is employed for (A) partial and total photoionization and photoRecombination cross sections of (e+ion) bound levels, and (B) DR and (e+ion) scattering cross sections. Relativistic effects and fine structure are considered in the Breit-Pauli approximation. Effects such as radiation damping may be taken into account where necessary. Unfiied Recombination cross sections are in excellent agreement with measurements on ion storage rings to about 10-20%. In addition to high accuracy, the strengths of the method are: (I) both total and level-specific cross sections and rate coefficients are obtained, and (II) a single (e+ion) Recombination rate coefficient for any given atom or ion is obtained over the entire temperature range of practical importance in laboratory and astrophysical plasmas, (III) self-consistent results are obtained for photoionization and Recombination; comprehensive datasets have been computed for over 50 atoms and ions. Selected data are presented for iron ions.Comment: 33 pages, 13 figures, Review in "Radiation Processes In Physics and Chemistry", Elsevier (in press). Postscript file with higher resolution figures at http://www.astronomy.ohio-state.edu/~pradhan/pr.p
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The Iron Project and the Rmax Project: Photoionization, Electron-Ion Recombination of Fe XVII and oscillator strengths for Fe XXII
Journal of Physics: Conference Series, 2009Co-Authors: Anil K. Pradhan, N. Nahar, Werner EissnerAbstract:The Iron Project and the Rmax Project aim in detail study of radiative and collisional processes of astrophysically abundant iron and iron-peak elements over a wide energy range from infra-red to X-rays. We will illustrate new features of high energy photoionization and high temperature Electron-Ion Recombination of Fe XVII that are more prominent than the low energy and low temperature. We have noted that core excitations to high lying levels introduce much stronger, high peak resonances than those to the low lying ones. We also report an extensive set of radiative transitions for Fe XXII. Oscillator strengths, line strengths, lifetimes and radiative decay rates for E1 transitions will be presented for 771 fine structure levels with 1/2 ≤ J ≤ 17/2. The parameters for a large set of forbidden E2, E3, M1, M2 transitions will also be presented.
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Self-consistent R-matrix approach to photoionization and unified Electron-Ion Recombination
Radiation Physics and Chemistry, 2004Co-Authors: N. Nahar, Anil K. PradhanAbstract:Abstract A unified scheme using the R-matrix method has been developed for electron–ion Recombination subsuming heretofore separate treatments of radiative and dielectronic Recombination (RR and DR). The ab initio approach within the coupled channel approximation has several inherent advantages in addition to the natural unification of resonant and non-resonant phenomena. It enables a general and self-consistent treatment of photoionization and electron–ion Recombination employing identical wavefunction expansion. Detailed balance takes account of interference effects due to resonances in cross sections, calculated explicitly for a large number of recombined (e+ion) bound levels over extended energy regions. The theory of DR by Bell and Seaton is adapted for high- n resonances in the region below series limits. The R-matrix method is employed for (A) partial and total photoionization and photoRecombination cross sections of (e+ion) bound levels, and (B) DR and (e+ion) scattering cross sections. Relativistic effects and fine structure are considered in the Breit–Pauli approximation. Effects such as radiation damping may be taken into account where necessary. Unified Recombination cross sections are in excellent agreement with measurements on ion storage rings to about 10–20%. In addition to high accuracy, the strengths of the method are: (I) both total and level-specific cross sections and rate coefficients are obtained, and (II) a single (e+ion) Recombination rate coefficient for any given atom or ion is obtained over the entire temperature range of practical importance in laboratory and astrophysical plasmas, (III) self-consistent results are obtained for the inverse processes of photoionization and Recombination; comprehensive datasets have been computed for over 50 atoms and ions. Selected data are presented for iron ions.
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Close-coupling R-matrix calculations for Electron-Ion Recombination cross sections
Journal of Physics B, 1999Co-Authors: Hong Lin Zhang, N. Nahar, Anil K. PradhanAbstract:Close-coupling (CC) calculations of Electron-Ion Recombination cross sections using the R-matrix method are presented and benchmarked with available experimental measurements. The Electron-Ion Recombination process, including resonant and non-resonant Recombination may be unified as a natural extension of the coupled-channel approximation, as traditionally employed for photoionization and Electron-Ion scattering. Recombination cross sections can be calculated to the same accuracy by employing similar eigenfunction expansions for the target ion. Detailed results are obtained for electron Recombination with C V, C VI, O VIII and Fe XXV. Several sets of theoretical calculations are reported and discussed: non-relativistic CC in LS coupling, relativistic CC in the Breit-Pauli approximation, with radiative attenuation and fine structure, and the relativistic distorted-wave approximation. The theoretical results are in very good agreement with highly accurate experimental measurements at the Heidelberg test storage ring for C V, C VI and O VIII, and the Electron-Ion beam trap at Livermore for Fe XXV. We discuss the overall effect of radiation damping of all resonances on effective cross sections and rates, important for H- and He-like ions. In addition to agreement with experimental data, the validity of the CC calculations is demonstrated by the continuity between the calculated photoRecombination, dielectronic Recombination and electron impact excitation cross sections. Certain issues related to the works of Badnell et al (1998 J. Phys. B: At. Mol. Opt. Phys. 31 L239) and Robicheaux (1998 J. Phys. B: At. Mol. Opt. Phys. 31 L109) are also addressed.
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Electron-Ion Recombination of Neutral Iron
The Astrophysical Journal, 1997Co-Authors: N. Nahar, Manuel A. Bautista, Anil K. PradhanAbstract:The total and state-specific Electron-Ion Recombination rate coefficients are obtained for Fe I. The calculations are carried out using a new ab initio method that incorporates both the radiative and the dielectronic Recombination processes in an unified and self-consistent manner. The computations employ the close coupling approximation and the R-matrix method from atomic collision theory. A 52 state close coupling eigenfunction expansion dominated by the states of the ground 3d64s and excited 3d7, 3d64p, 3d54s2, and 3d54s4p configurations of Fe II are used in the present calculations. The important electron correlation and radiation damping effects are included via explicit coupling of autoionization and radiative channels. This is the first detailed atomic calculation for the Recombination rates for Fe I. The present rates are considerably higher than the radiative Recombination rates being used currently in the low-temperature region, T ≤ 104 K, whereas they are about 4 times lower than those given by the Burgess general formula for dielectronic Recombination at higher temperatures. The implications of the new Recombination rate coefficients and photoionization cross sections for Fe I on the ionization structure of iron in the cold neutral interstellar medium are studied. It is found that the ratio of Fe II to Fe I obtained with the new atomic data increases by a factor of about 3-30 over previous calculations.