Effect of dielectronic recombination excitation in the solar chromosphere-corona transition region

The intensities of lines emitted from the solar chromosphere-corona transition region and observed on the earth are calculated by considering excitation of electrons to the upper level caused by electron-impact excitation and dielectronic recombination excitation processes. For the lines under investigation, the electron-impact deexcitation rates are negligibly small in comparison with spontaneous transition probabilities. Hence, electrons from the upper level deexcite through spontaneous transition only, emitting photons of wavelength corresponding to the energy difference between two levels. To determine the contribution of dielectronic recombination excitation (DRE) to the excitation mechanism, the calculations are repeated with exclusion of DRE. It is found that DRE contributes significantly and that its contribution may be much larger than that of electron-impact excitation.     

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.     

Density effects on the spectral intensities of dielectronic satellite line in dense plasmas

Summary In this paper we present a theoretical analysis of the spectral intensity of dielectronic satellite lines in dense plasmas. The ion microfield causes an oscillator strength mixing that alters the spectral intensity of such a transition. Numerical calculations of this high-density effect have been performed for the most intense 2l2l′→1s2l He-like transitions.

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Riassunto In questo articolo si presenta un'analisi teorica dell'intensità spettrale delle linee di satellite dielettroniche in plasmi densi. Il microcampo ionico causa un mescolamento delle forze dell'oscillatore che modifica l'intensità spettrale di una tale transizione. Si sono effettuati calcoli numerici di questo effetto ad alta densità per le transizioni più intense del tipo 2l2l′→1s2l.

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Резюме В этой работе мы предлагаем теоретический анализ спектральной интенсивности диэлектронных линий сателлитов в плотной плазме. Микрополе иона вызывает смешивание сил осцилляторов, что изменяет спектральную интенсивность такого перехода. Проведены численные вычисления эффекта высокой плотности для наиболее интенсивных Не-подобных переходов 2l2l′→1s2l.

     

Effect of dielectronic recombination on the charge-state distribution and soft X-ray line intensity of laser-produced carbon plasma

The effect of dielectronic recombination in determining charge-state distribution and radiative emission from a laser-produced carbon plasma has been investigated in the collisional radiative ionization equilibrium. It is observed that the relative abundances of different ions in the plasma, and soft X-ray emission intensity get significantly altered when dielectronic recombination is included. Theoretical estimates of the relative population of CVI to CV ions and ratio of line intensity emitted from them for two representative formulations of dielectronic recombination are presented.     

Recent dielectronic recombination experiments

New recombination experiments with merged cold beams of electrons and atomic ions have been carried out at the storage ring facilities TSR in Heidelberg, ESR in Darmstadt, and CRYRING in Stockholm. A brief overview is given on the recent activities in which the Giessen group was engaged. Topics of this research were dielectronic recombination (DR) of astrophysically relevant ions, recombination of highly charged ions with respect to cooling losses in storage rings, field effects on DR, search for interference effects in photorecombination of ions, correlation effects in DR of low-Z ions, spectroscopy of high-Z ions by DR, and lifetimes of metastable states deduced from DR experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radiative recombination of excitons in semiconductors at high excitation intensities

The shape of the exciton luminescence band of the gaseous phase of free excitons in crystal Si is investigated under high level excitation. Only the exciton-exciton interaction is considered and the influence of collisions of excitons with phonons and electrons is not taken into account. The theoretical shape of the exciton luminescence band qualitatively agrees with experiment. The process of the radiative Auger-recombination of two indirect excitons without the participation of phonons is studied in Ge and Si. The expression for the frequency and temperature dependence of the probability of radiation is obtained. The band has the asymmetrical Gaussian form with the steep short-wave tail. The predicted luminescence band in Ge is shifted at the long-wavelength side from the well-known exciton luminescence bands with participation of the phonons. The selection rules for the probability amplitude of the process under consideration are obtained.     

Angular distribution of photons in dielectronic recombination

We have calculated the angular distribution of photons emitted after dielectronic recombination of highly charged uranium ions and obtained differential cross sections for resonant transfer and excitation in collisions of U⁹⁰⁺ with C atoms using the impulse approximation. This revised version was published online in July 2006 with corrections to the Cover Date.     

高离化态Cu18+离子的双电子复合及共振转移激发过程的理论研究

在准相对论理论框架下计算了Cu18+离子的双电子复合截面,分析了组态相互作用对截面的影响.基于这些数据,在冲量近似下,通过对靶原子中电子动量分布的卷积,进一步得到了Cu18+与H2碰撞过程中的共振转移激发截面,并与已有的实验结果作了比较,符合得很好.     

Tables for the computation of dielectronic recombination coefficients

Two sets of tables are presented which facilitate the rapid calculation of hydrogenic ion dielectronic recombination coefficients for ions of charge z?17 and for ions of charge z>17     

Many-body perturbation theory applied to dielectronic recombination resonances

A procedure to calculate dielectronic recombination cross-sections based on relativistic many-body perturbation in an all order formulation is presented. Complex rotation is employed in order to handle autoionizing states. The method is applied to recombination of lithium-like neon and lithium-like argon and the results are compared with experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

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.     

Field enhanced dielectronic recombination of Si11+ ions

The enhancement of dielectronic recombination by applied electric fields has been observed and measured for the first time in a wide range of controlled and measurable fields using multiply charged ions. The heavy ion storage ring, CRYRING, at Stockholm University was used to store a beam of Si¹¹⁺ and collide it with a cold electron target. The observation of a substantial monotonic increase of the rate coefficient for the group of higher Rydberg states is in puzzling disagreement with theoretical calculations of electric field enhanced dielectronic recombination. This revised version was published online in July 2006 with corrections to the Cover Date.