Theoretical Study On The Electron-ion Resonant Recombination Process Of Highly Charged Si And Fe Ions

Electron-ion resonant recombination,such as dielectronic recombination(DR)and higher-order trielectronic recombination(TR)and quadruelectronic recombination(QR)etc.is a fundamental atomic dynamics process in high-temperature astronomical,laboratory plasmas.Understanding the properties of astrophysical and laboratory plasmas necessitates knowing the ionization balance of the observed spectrum.In recent years,based on experimental devices such as heavy-ion storage ring and electron-beam ion trap and the development of high-resolution measurement technology,many experiments have been carried out on highly charged ions and electron collision,which including some high-order TR and QR processes that have been ignored in the past.The analysis and identification of these experimental spectrum observation results and the exploration of their internal mechanisms require detailed theoretical research.In this paper,based on the relativistic configuration interaction(RCI)theory,we using the FAC code systematically study the resonant recombination process of highly charged ions(Si¹⁰⁺,Fe¹⁴⁺).In the calculations,by carefully considering the electron correlation effects,Breit interaction and QED effects,this paper carried out theoretical research on the most abundant silicon and iron elements in cosmos.It mainly includes the following two works:Firstly,the coefficients of electron-ion resonant recombination process are calculated for the ground state of Si¹⁰⁺ions(1s²2s^{2 1}S₀).Our attentions are mainly focusing on K-shell 1s?2l((?)n=1)transition as well as L-shell 2s?3l((?)n=1),and2s?4l((?)n=2)transitions.The resonance strength,resonance energy,Auger rates,radiative transition rates are calculated.For the dominate resonant states 1s2l³nl',1s²2l3lnl',and 1s²2l4lnl'are given.The present results are compared with the NIST data,it is found that the difference is less than 2.08%for the Si⁹⁺ions,and 4.03%for the Si¹⁰⁺ions,respectively.We simulate the TSR experiments in German by Bernhardt,and found that the theoretical results agree well with the experiments.For the excitation of the L-shell,corresponding to temperaturesk _BT_^=5 e V perpendicular to the confining magnetic field andk_B T_P=0.093 me V parallel to the magnetic field are chosen in the convolution of our results.The resonant recombination spectrum is mainly distributed in the lower energy range of 50-400 e V,which is mainly from 2s?3l transition.TR process makes an important contribution to the rate coefficient about 8.98%.For the excitation of the K-shell,the electron temperatures convolution parameters are k _BT_P=0.093 me V,k _BT_^=0.5 e V,respectively.The resonant recombination spectrum is distributed in the 1350-1850 e V higher energy range.Considering the multi-electron correlation in the higher-order process,it is found that it affects the resonance strength but does not have a significant effect on the total rate coefficient.In order to consider the electron distribution in the storage ring experiments,the contribution of the metastable state(1s²2s2p ³P₀t=16.64s)to the rate coefficients is considered in our calculations,and it is found that it cannot be neglected in the experimental spectrum.Secondly,the electron-ion resonant recombination process of the electron excitation(?)n=1 transition in the L-shell of Fe¹⁴⁺ion(1s²2s²2p⁶3s^{2 1}S₀)has been systematically studied.In the theoretical calculation,three electron correlation models(Model I,II,III)were built to gradually expand the electron correlation configurations and research its influence on resonance strength and rate coefficient.In Model I,only the dielectronic resonant excited states produced in DR process are considered.On the basis of Model I,Model II also includes the trielectronic resonant excited states generated in TR process.On the basis of Model II,Model III further considers the quadruelectronic resonant excited states generated in QR process.The results show that the strong electron correlation effect has a very important influence on the resonant recombination spectrum of Fe¹⁴⁺ions.Under the three models,the calculation results of Model II and Model I show that although the resonance energy changes little,the strength decreases by about one order of magnitude.Model III is close to Model II.By using the temperatures convolution parametersk _BT_P=0.2 me V,andk _BT_^=1.6 e V,respectively.We analysis the spectrum of the Fe¹⁴⁺ion DR process,and identify some strong peaks.The experimental spectrum is carried out at Heidelberg TSR by Bernhardt et al.It is found that the strongest peaks in the experimental spectrum mainly come from the transition of 2p-3d.In previous studies,due to the lack of theoretical calculations,Bernhardt generally believed that there was no high-order TR process in the resonant recombination spectrum of Fe¹⁴⁺ions.This paper reveals for the first time that there is a strong TR process in the resonant spectrum of Fe¹⁴⁺ions at 400-800 e V,the contribution is about 24.1%.In this paper,the contribution of metastable state ion(1s²2s²2p⁶3s3p ³P₀)to the rate coefficient is also considered.Combined with the ion population in the storage ring(94%1s²2s²2p⁶3s^{2 1}S₀+6%1s²2s²2p⁶3s3p ³P₀),the rate coefficient of DR and the rate coefficient in the plasma environment are calculated,which agree well with the experimental results.