Study Of Resonance Features In Photoionization And Photorecombination Of Li- And He-like C,Fe And Ni Ions

Photoionization and photorecombination play a vital role to get a deep insight of the interactions of photon and electron with the atoms or ions.However,the accurate calculations of these processes offer serious challenges to atomic physics community.The present work is based on the strong motivation of understanding these fundamental atomic processes by performing detailed calculations for the He-and Li-like ions.In this thesis we present photoionization cross sections of the ground and excited states of Li-like Carbon(C ?)in the framework of fully relativistic R-matrix formalism as implemented in Dirac atomic R-matrix code.For target wavefunctions expansion,comprehensive Multi configuration Dirac Hartree Fock(MCDHF)calculations with an option of extended optimal level,are performed for the lowest 17 target states of He-like Carbon(C ?)arising from 1s2 and 1snl,with n=2,3 and l=s,p,d configurations.Our target energy levels and transition parameters belonging to these levels are ascertained to be in excellent agreement with the experimental and the well established theoretical results.We use the principle of detailed balance to get the photorecombination cross sections of the ground state of C v.Both photoionization and photorecombination cross sections manifest important KLL and KLM resonance structures.We present detailed analysis of the KLL and KLM resonances by comparing resonance parameters of each resonance with available theoretical and experimental results.We find very good agree-ment for the resonance parameters with the accurate measurements at Advanced Light Source(ion photon end beam station)and CRYRING(synchrotron storage ring).Moreover,in the present work we analyze the dielectronic recombination which is characterized by the radiative decay of a doubly excited autoionizing state in the pho-torecombination(PR)process.We calculate PR cross sections for the ground states of the Fe ??? and Ni ??? ions by employing the Dirac R-matrix technique.The autoionizing states are treated in the framework of Davies and Seaton's theory to ac-count for the radiative decay.The strengths of the KLL resonances that equate directly to the dielectronic satellite line strengths are evaluated.Besides,the Multi configura-tion Dirac Fock(MCDF)formalism is utilized to obtain the dielectronic satellite line strengths under the isolated resonance approximation.A Very good agreement is found for the wavelengths and transition parameters belonging to the KLL autoionizing states with the previous theoretical and experimental results.The dominant KLL dielectronic satellite line strengths from both theoretical models are consistent with each other and are in good agreement with the established theoretical models and measurements at the electron beam ion trap(EBIT).