Energy levels, lifetimes and wavefunction compositions have been computed for all levels of odd parity 4s24p5 ground configuration as well as 4s4p6 and 4s24p44d even parity excited configurations in Br-like Sr IV, Y V, Zr VI, Nb VII and Mo VIII. Transition probabilities, oscillator strengths and line strengths for the electric dipole (E1) transition from the 4s24p5 configuration have been obtained using the multiconfiguration Dirac–Fock approach. Correlations within the n = 4 complex, Breit and quantum electrodynamics effects have been included. We make a detailed comparison of our results with those of other numerical methods and experiments to assess the quality of our results. Good agreement is observed between our results and those obtained using different approaches confirm the quality of our results. Further, we have also predicted new atomic data that were not available so far and are yet to be observed.

Aims. The present study aims to provide a diagnostic line ratio that will enable the observer to determine whether a plasma is in a state of transient ionization.Methods. We use the Atomic Data and Analysis Structure (ADAS) to calculate line contribution functions for two lines, Si iv 1394 Å and O iv 1401 Å, formed in the solar transition region. The generalized collisional-radiative theory is used. It includes all radiative and electron collisional processes, except for photon-induced processes. State-resolved direct ionization and recombination to and from the next ionization stage are also taken into account.Results. For dynamic bursts with a decay time of a few seconds, the Si iv 1394 Å line can be enhanced by a factor of 2-4 in the first fraction of a second with the peak in the line contribution function occurring initially at a higher electron temperature due to transient ionization compared to ionization equilibrium conditions. On the other hand, the O iv 1401 Å does not show such any enhancement.Thus the ratio of these two lines, which can be observed with the Interface Region Imaging Spectrograph, can be used as a diagnostic of transient ionization. Conclusions. We show that simultaneous high-cadence observations of two lines formed in the solar transition region may be used as a direct diagnostic of whether the observed plasma is in transient ionization. The ratio of these two lines can change by a factor of four in a few seconds owing to transient ionization alone.

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Collision strengths for the lowest 52 fine-structure levels of Ba XLVIII have been computed using Dirac atomic R-matrix code (DARC). Resonances in the threshold region have been completely resolved and the contributions of these resonances to allowed and forbidden transitions have been presented. Effective collision strengths have also been determined within a temperature range from the ground state. Collision strengths from ground state have also been computed with the relativistic distorted wave method, the flexible atomic code (FAC) was used for checking the accuracy of our results. The present work represents a new and significant work with improvement in the field. We believe that our presented data of collision and effective collision strengths may be useful in the future for benchmark calculations and for plasma diagnostics.

Energy levels, wavefunction compositions, and lifetimes are computed for all levels of 4s24p5, 4s24p44d, and 4s4p6 configurations in Br-like ions (Z = 47–50). We use the multiconfigurational Dirac–Fock method to generate the wavefunctions. We also present the transition wavelengths, oscillator strengths, transition probabilities, and line strengths for the electric dipole (E1) transition from the ground state configuration. We compare our calculated results with the available data in the literature and good agreement is obtained, which confirms the quality of our results. Moreover, we predict some new atomic data that have not been available so far and may be important for plasma diagnostic analysis in fusion plasma.

Configuration interaction calculation has been performed for excitation energies, oscillator strengths, and transition probabilities of 114 fine-structure levels of sulphur-like titanium. The relativistic effects are included in Breit–Pauli approximation by adding mass-correction, Darwin, and spin–orbit interaction terms to the nonrelativistic Hamiltonian. We have adjusted the diagonal elements of Hamiltonian matrices (fine-tuning) before the calculation of oscillator strength and transition probabilities for the electric dipole allowed transitions. Our calculated data are in close agreement with data listed in National Institute of Standards and Technology and other available results. Correct identification of some of the levels become very difficult because of strong mixing among several fine-structure levels. We predict new energy levels, oscillator strength, and transition probability data, where no other theoretical or experimental results are available, which will form the basis for future experimental work.

Collision strengths for all 1326 transitions among lowest 52 fine-structure levels of Br XXVII have been computed using Dirac atomic R-matrix code (DARC). Resonances in the threshold region have been completely resolved and the contributions of these resonances to allowed and forbidden transitions have been presented. The partial collision strength for each angular momentum has been studied graphically. Effective collision strengths have also been determined within the temperature range for all 1326 transitions among the lowest 52 levels. Target state energies of the lowest 52 fine-structure levels have been computed from the multi-configuration Dirac–Fock method (MCDF). Additionally, similar calculations with the relativistic distorted wave method and flexible atomic code (FAC) have also been performed to check the accuracy of our results. The present work represents a new and significant work with improvement in the field. We believe that our presented data of collision and effective collision strengths may be useful in the future for benchmark calculations and for plasma diagnostics.

We discuss the diagnostic potential of high cadence ultraviolet spectral data when transient ionization is considered. For this we use high cadence UV spectra taken during the impulsive phase of a solar flares (observed with instruments on-board the Solar Maximum Mission) which showed excellent correspondence with hard X-ray pulses. The ionization fraction of the transition region ion O v and in particular the contribution function for the O v 1371Å line are computed within the Atomic Data and Analysis Structure, which is a collection of fundamental and derived atomic data and codes which manipulate them. Due to transient ionization, the O v 1371Å line is enhanced in the first fraction of a second with the peak in the line contribution function occurring initially at a higher electron temperature than in ionization equilibrium. The rise time and enhancement factor depend mostly on the electron density. The fractional increase in the O v 1371Å emissivity due to transient ionization can reach a factor of 2-4 and can explain the fast response in the line flux of transition regions ions during the impulsive phase of flares solely as a result of transient ionization. This technique can be used to diagnostic the electron temperature and density of solar flares observed with the forth-coming Interface Region Imaging Spectrograph