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The study of atomic spectroscopy and collision processes in a dense plasma environment has gained a considerable interest in the past few years due to its several applications in various branches of physics. The multiconfiguration Dirac-Fock (MCDF) method and relativistic configuration interaction (RCI) technique incorporating the uniform electron gas model (UEGM) and analytical plasma screening (APS) potentials have been employed for characterizing the interactions among the charged particles in plasma. The bound and continuum state wavefunctions are determined using the aforementioned potentials within a relativistic Dirac-Coulomb atomic structure framework. The present approach is applied for the calculation of electronic structures, radiative properties, electron impact excitation cross sections and photoionization cross sections of many electron systems confined in a plasma environment. The present study not only extends our knowledge of the plasma-screening effect but also opens the door for the modelling and diagnostics of astrophysical and laboratory plasmas.

Photoionization cross-section results for the ground state 2 p 6 3 s ( 2 S 1/2 ) along with the lowest four excited states 2 p 6 3 p ( 2 P o 1/2, 3/2 ) and 2 p 6 3 d ( 2 D 5/2, 3/2 ) of Na-like Si IV are reported by employing the close-coupling Breit–Pauli R-matrix (BPRM) method. The target state wavefunctions of Si V ion have been obtained using the configuration interaction method (CIV3) in the LSJ-coupling scheme. Relativistic effects and all key physical effects such as short-range correlations, exchange and channel coupling are considered in the computations. Our evaluated target state energies of the Si V core ion show close agreement with the NIST database. Quigley and Berrington (QB) technique is applied to determine resonance positions ( E r ) and autoionization line widths (Γ) with quantum defects caused by the removal of the 2 p electron from 2 s 2 2 p 6 3 s 2 S 1/2 , the ground state of Si IV. To the best of our understanding, the study presented here details thorough relativistic photoionization calculations for this system for the first time. We hope that our results will be valuable to astrophysical and laboratory plasma modeling and diagnosis. Graphical Abstract Photoionization cross-sections (σ) for the ground state 2 p 6 3 s ( 2 S 1/2 ) of Si IV.

Relativistic calculations of the photoionization cross-sections are carried out for the ground state 1 s 2 2 p 6 3 s 2 ( 1 S 0 ) and first three excited states 1 s 2 2 p 6 3 s 3 p ( 3 P 0 , 1 , 2 o ) of Mg-like Ca IX ion using the Breit–Pauli R -matrix (BPRM) approach. Configuration interaction method (CIV3) is used to construct the target wavefunctions. A total of lowest lying 21 fine structure levels corresponding to 2 p 6 nl (3 ≤  n  ≤ 5) configurations are considered for the expansion of target wavefunctions. Reported target state eigen energies of the 21 fine structure levels of core ion Ca X agree with the available data. To assess the accuracy of our BPRM results, we have also performed similar calculations using the fully relativistic Dirac atomic R -matrix code (DARC) for the ground state of Mg-like Ca IX ion. Further, relativistic distorted wave (DW) method is also used for the comparison purpose, and a good agreement has been found with the R -matrix results. The quantum number ( n ), resonance width (Γ) and resonance energies ( E r ) of the 3 dnp ( 3 P 1 , 1 P 1 , 3 D 1 , 1 D 2 ), 3 dnf ( 3 P 1 , 1 P 1 ) and 4 snp ( 3 P 2 , 3 P 0 , 3 P 1 , 1 P 1 ) series have also been predicted using Quigley and Berrington (QB) method. We believe that the present results will be helpful for modeling and diagnostics of laboratory and astrophysical plasmas.

Excitation energies, lifetimes and radiative data including line strengths, oscillator strengths, transition wavelengths and transition probabilities have been reported for electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions for Na-like Ca X ion. These extensive calculations for 1s 2 2s 2 2p 6 nl configurations (n = 1 to 7 and l = 0 to 4) of Na like Ca X have been made using multi-configuration Dirac–Fock (MCDF) method. The effect of Breit-interaction and quantum electrodynamics (QED) on energy levels has also been discussed in graphical form. Shift in energy levels due to correlation effects, namely core-valence correlation and valence-valence correlation has also been reported. Further, similar calculations have also been made using the configuration interaction technique (CIV3) and relativistic configuration interaction (RCI) technique to ensure the accuracy of our results. Our calculated results are in good agreement with the available experimental and theoretical data. Plasma parameters like electron density, plasma frequency, coupling parameter and skin depth for the spectral lines 1s 2 2s 2 2p 6 3s  2 S 1/2   –1s 2 2s 2 2p 6 3p 2 P 3 / 2 o (1–3) and 1s 2 2s 2 2p 6 3s 2 S 1/2 –1s 2 2s 2 2p 6 3p 2 P 1 / 2 o (1–2) have also been studied for hot dense plasma. We have also reported the line intensity ratio for the spectral lines 1–3 and 1–2. The influence of plasma temperature on the relative population for 1st 2 excited states, partition function and thermodynamic parameters have also been studied. The present results will be helpful in astrophysical plasmas, modelling and characterization of hot dense plasma.

In order to quantify the Indian summer monsoon (ISM) variability for a monsoon dominated agrarian based Indian socio-economy, we used combined high resolution δ 13 C, total organic carbon (TOC), sediment texture and environmental magnetic data of the samples from a ~3 m deep glacial outwash sedimentary profile from the Sikkim Himalaya. Our decadal to centennial scale records identified five positive and three negative excursions of the ISM since last ~13 ka. The most prominent abrupt negative ISM shift was observed during the termination of the Younger Dryas (YD) between ~11.7 and 11.4 ka. While, ISM was stable between ~11 and 6 ka, and declined prominently between 6 and 3 ka. Surprisingly, during both the Medieval Warm Period (MWP) and Little Ice age (LIA) spans, ISM was strong in this part of the Himalaya. These regional changes in ISM were coupled to southward shifting in mean position of the Intertropical Convergence Zone (ITCZ) and variations in East Asian monsoon (EAM). Our rainfall reconstructions are broadly in agreement with local, regional reconstructions and PMIP3, CSIRO-MK3L model simulations.