*University of Delhi*

In recent years, the high quality observational data recorded by space missions such as International Ultraviolet Explorer (EUVE), the Advanced Satellite for Cosmology and Astrophysics (ASCA), the Hopkins Ultraviolet Telescope (HUT), the Hubble Space Telescope (HST), and Solar and Heliospheric Observatory (SOHO), has highlighted the need for highly accurate atomic data. There is no doubt that this situation will be further emphasized by the launch of future space missions such as FUSE. The accuracy of atomic data is crucial for the interpretation of the spectra from these missions in terms of the physical conditions in the astrophysical sources. The need for accurate atomic and molecular data is immense, with applications in such diverse fields such as astronomy, fusion research, and lasers. The type of data depends upon the region or the object being studied. As very few of the ions of interest can be studied experimentally in the laboratory, the user must depend primarily on theoretical data. Nowadays, measurement and calculation of photoionization cross section and collision strength has become a subject of great interest. Photoionization cross sections are necessary for the computation of photoionization and recombination rates for ionization balance in astrophysical plasmas. Accurate electron-impact inner-shell ionization cross section data are necessary for precisely measuring the impurity density in fusion plasma.

In this direction, our group is involved in the calculations of accurate collision strengths, radiative and autoionization decay rates, photoionization cross-sections, oscillator strengths and wavelengths for allowed and forbidden transitions which are needed for the interpretation of observational data and for modeling of astrophysical objects. In our calculations, important physical effects mainly configuration interaction, autoionizing resonances, exchange, coupling and relativistic effects are incorporated by using Configuration Interaction Technique for the atomic structure and accurate R-matrix method for the collisions. For atomic structure calculations, we use grasp2k, GRASP, FAC, CIV3 techniques whereas for collision problems we use very sophisticated R-Matrix (both relativistic and non-relativistic) state of art techniques. We have reported energies and radiative data for E1, E2, M1 and M2 multipole transitions for lowest 110 fine structure levels of the Cs XXV ion. We have identified 46 EUV and 33 SXR spectral lines from ground state. We have predicted many new spectral lines, which are yet to be observed, and which will form the basis for the future experimental work. We have also calculated line intensity ratio (*R* ) and electron density and studied their behavior graphically with high plasma temperatures.Moreover, for providing support to experimentalists and extend the data base, we reported the atomic data for Ne-like ions (*Z* = 72-75) by calculating energies and lifetimes for 209 fine structure levels of HfLXIII, Ta LXIV, W LXV and Re LXVI, along with 109 fine structure levels available in the literature for W LXV.Tungsten being a plasma facing material in fusion reactors, EUV and SXR transitions of high Z ions are of Astrophysical interest. Therefore, we have reported the atomic data for W XLIV such as energies for the lowest 100 fine structure levels. Additionally, the radiative data for all E1 and M1 transitions from ground state among the lowest 100 levels were tabulated. We have identified 5 EUV and 38 SXR spectral lines in dipole transitions. We have calculated the line intensity ratio by considering the maximum plasma temperature of 1010 K, which increases with increasing temperature. For *T* ≥ 109K, the increase in *R* < 0.001%. This information may be useful for producing optically thin plasma in LTE at higher temperatures for W XLIV.

*Man Mohan (Professor in Physics)**Avnindra Kumar Singh (Group Leader at DDU College, Associate Professor in Physics)**Anil K.Pradhan (Professor in Department of Astronomy, Ohio State University)**Sultana N. Nahar (Research Professor in Department of Astronomy, Ohio State University)**Alok Kumar Singh Jha (Assistant Professor in Physics)**Nupur Verma (Associate Professor in Physics)**Dishu Dawra (Doctoral Student)**Mayank Dimri (Doctoral Student)*

Professor Man MOHAN
*Department of Physics and Astrophysics, Delhi University, Delhi 110007, India*

Email: drmanmohan.05@gmail.com

- [1] S. Aggarwal et al., "Photoionization Cross-Section of Chlorine-like Iron",
*Journal of Astrophysics and Astronomy***33**, 291-301 (2012). - [2] A. Goyal et al., "Atomic structure calculations for Br-like ions",
*Canadian Journal of Physics***93**, 487-495 (2015). - [3] A. Goyal et al., "Atomic structure calculations and identification of EUV and SXR spectral lines in Sr XXX",
*Journal of Quantitative Spectroscopy and Radiative Transfer***161**, 157-170 (2015). - [4] I. Khatri et al., "R-matrix calculations of photoionization cross section of Ne-like tungsten",
*Canadian Journal of Physics***93**, 1221-1226 (2015). - [5] S. Aggarwal et al., "Relativistic atomic data for W XLVII",
*Chinese Physics B***24**, 053201 (2015). - [6] A. Goyal et al., "Calculation of energy levels, lifetimes and radiative data for La XXIX to Sm XXXIV",
*Atomic Data and Nuclear Data Tables***107**, 406-456 (2016). - [7] I. Khatri et al., "Energy levels and radiative transition rates for Ba XLVIII",
*Atomic Data and Nuclear Data Tables***107**, 367-405 (2016). - [8] I. Khatri et al., "MCDHF calculations and study of plasma parameters for Li-like ions",
*Radiation Physics and Chemistry***123**, 46-54 (2016). - [9] I. Khatri et al., "Multi-Configuration Dirac–Hartree–Fock (MCDHF) Calculations for B-Like Ions",
*Atoms***4**, 13 (2016). - [10] A. Goyal et al., "Atomic Structure Calculations and Study of Plasma Parameters of Al-Like Ions",
*Atoms***4**, 22 (2016). - [11] A. Goyal et al., "Atomic structure calculations and study of line intensity ratio for Kr XXIV",
*Canadian Journal of Physics***94**, 712-723 (2016). - [12] A. Goyal et al., "Atomic structure calculations and study of EUV and SXR spectral lines in Cu-like ions",
*Canadian Journal of Physics***94**, 839-852 (2016). - [13] A. Goyal et al., "Spectroscopic study of EUV and SXR transitions of Cs XXV",
*Canadian Journal of Physics***96**, 871-877 (2018). - [14] A. Goyal et al., "Fully relativistic atomic structure calculations for W XLIV for determination of plasma diagnostic terms",
*Canadian Journal of Physics***95**, 950-957 (2017). - [15] A. Goyal et al., "Collision strength and effective collision strength for Br XXVII",
*Canadian Journal of Physics***95**, 1127-1135 (2017). - [16] I. Khatri et al., "Photoionization of Cl-like Ni XII using relativistic R-matrix close-coupling method",
*Canadian Journal of Physics***95**, 1136-1141 (2017). - [17] M. Mohan et al., "Collision strength and effective collision strength for Ba XLVIII",
*Canadian Journal of Physics***95**, 173-178 (2017). - [18] A. Singh et al., "Accurate study on the properties of spectral lines for Na-like Cr
^{13+}",*Canadian Journal of Physics*, cjp-2018-0218 (2018). - [19] A. Singh et al., "Spectroscopic study of EUV and SXR transitions of Cu XIX with plasma parameters",
*Radiation Physics and Chemistry***156**, 174-192 (2019).