Sabyasachi Kar

Polarizabilities of Li and Na in Debye plasmas

We have carried out calculations to investigate the effect of Debye plasmas on the dipole, quadrupole, octupole polarizabilities of lithium and sodium atoms using the symplectic algorithm in the framework of the pseudo-state summation technique. The polarizabilities of alkali-metal atoms for various Debye lengths are reported for the first time in the literature. The behavior of the transition energies and oscillator strengths for Li and Na in plasma environments is also presented. In free atomic cases, our calculated results are in good agreement with the reported theoretical and experimental results.

Effect of screened Coulomb potentials on the resonance states of two-electron highly stripped atoms using the stabilization method

Resonance states of C4+, O6+, Ne8+ ions interacting with screened Coulomb potentials have been investigated using the stabilization method. We employ highly correlated exponential basis functions for S-, P-state calculations and employ CI-type basis functions for D-state calculations. We report a total of seven S-wave resonances of which four belong to 2sns (n = 2, 3, 4, 5) series and three belong to the 2pnp (n = 2, 3, 4) series. In addition, a total of eight P-wave resonances of which three belong to 2snp+ (n = 2, 3, 4), three belong to the 2snp− (n = 3, 4, 5) series, two belong to the 2pnd (n = 3, 4) and the lowest D-wave resonance for each systems and each screening parameters below the n = 2 thresholds of the respective subsystems are reported. In the unscreened case, we have found some resonance states that have not been reported before. In the screened case our reported results are new and show some interesting behaviour with and without electron–electron screening.

Doubly excited states of the hydrogen negative ion and helium atom in astrophysical plasmas

The nonthermal effects on the doubly excited resonance states of the hydrogen negative ion and helium atom are investigated in Lorentzian astrophysical plasma environments using highly correlated Hylleraas-type wave functions in the framework of the stabilization method. Resonance parameters (resonance position and width) are reported for the first time as functions of the spectral index and plasma parameter. The screening effects are more pronounced in the stronger screening region.

Energies and transition wavelengths for Li II, Be III, B IV, C V embedded in Debye plasmas

We have carried out non-relativistic calculations to investigate the effect of Debye plasmas screening on the doubly excited nonautoionizing 1,3Pe and 1,3Do states of Li II, Be III, B IV, and C V using highly correlated exponential wave functions within the framework of Ritz variational principle. The 2p2 3Pe, 2p3p 1Pe, and 2p3d 1,3Do states energies, and wavelengths for the 2p3p 1Pe → 2p3d 1Do, 2p2 3Pe → 2p3d 3Do, 2p3p 3Pe → 2p3d 3Do, and 2p3p 3Pe → 2p3d 3Do transitions for different Debye lengths are reported. Comparisons are made with the existing results. Results for B IV and C V for different screening parameters are reported for the first time in the literature. Transition wavelengths show interesting behavior with increasing screening parameters and nuclear charge.

Resonances in electron-hydrogen scattering in Debye plasmas

We have investigated the influence of Debye plasmas on resonance states in electron?hydrogen scattering using highly correlated exponential wavefunctions in the framework of the stabilization method. Resonance parameters (resonance positions and widths) below the N = 2 H threshold are reported for selected screening parameters. Critical values of the screening parameters are reported from which S, P, D Feshbach resonances are transformed to shape resonances. Behaviour of the resonance widths obtained from this work as a function of screening parameters is in agreement with the recently reported work for weaker screening, but not in close agreement with those for stronger screening.

Doubly-excited 1,3De resonance states of two-electron positive ions Li+ and Be2+ in Debye plasmas

We investigate the bound 1,3D states and the doubly-excited 1,3De resonance states of two-electron positive ions Li+ and Be2+ by employing correlated exponential wave functions. In the framework of the stabilization method, we are able to extract three series (2pnp, 2snd, 2pnf) of 1De resonances and two series (2pnp, 2snd) of 3De resonances below the N = 2 threshold. The 1,3De resonance parameters (resonance energies and widths) for Li+ and Be2+ along with the bound-excited 1s3d 1,3D state energies are reported for the first time as functions of the screening parameter. Accurate resonance energies and widths are also reported for Li+ and Be2+ in vacuum. For free-atomic cases, comparisons are made with the reported results and few resonance states are reported for the first time.

Dynamic dipole polarizabilities of H− and Ps− in weakly coupled plasmas

The effects of weakly coupled plasmas on the dynamic dipole polarizabilities of the H− and Ps− ions are investigated using highly correlated exponential wave functions. The Debye-Huckel shielding approach of plasma modeling is used to represent weakly coupled plasma environments. In free-atomic cases, results obtained from the present study for H− are in agreement with the available calculations and results for Ps− are reported for the first time. Frequency-dependent polarizabilities of H− and Ps− as functions of screening parameter are also presented for the first time.

Resonances in positron-hydrogen scattering in dense quantum plasmas

We have investigated the S-wave resonance states in positron-hydrogen system embedded in dense quantum plasmas using Hylleraas-type wave functions within the framework of the stabilization method. The effect of quantum plasmas has been incorporated using the exponential-cosine-screened Coulomb (modified Yukawa-type) potential. Resonance parameters (both position and width) below the Ps n = 2 threshold are reported as functions of plasma screening parameters.

Doubly excited P, D and F unnatural parity states of hydrogen negative ion using correlated wavefunctions

We have investigated the doubly excited 1,3Pe, 1,3D° and 1,3Fe states of the hydrogen negative ion using highly accurate correlated wavefunctions. The doubly excited 2p2 3Pe metastable bound state (so-called second bound state) energy of H− is obtained using the Ritz variational principle. The upper bound of the energy of the 2p2 3Pe bound states is −0.125 355 451 242 au, which is comparable with the available best results −0.125 355 451 24 (Bylicki M and Bednarz E 2003 Phys. Rev. A 67 022503). We employ the complex-coordinate rotation method to extract resonance parameters. The resonance parameters (both resonance position and width) of H− for 1,3Pe, 1,3D° below the n = 3, 4, 5, and 6 thresholds and 1,3Fe states below the n = 4, 5, and 6 thresholds are reported. We have also employed the stabilization method to extract resonance parameters for the 1,3Pe states. In addition to Feshbach resonances lying below the n = 3, 4, 5, 6 hydrogen thresholds, we have calculated one 3D° shape resonances lying above the H (n = 3) threshold. Resonance parameters obtained from present work are comparable with the reported results using CI-type basis functions and hyperspherical potential curves. The 1Pe resonance state, and some of 1,3Pe, 1,3D°, 1,3Fe resonance states are reported for the first time using the explicitly correlated exponential wavefunctions.

Isotope shift for the 1De autodetaching resonance in H− and D−

The doubly excited 1De resonance state of H− below the n = 2 threshold has been investigated using highly correlated exponential basis functions in the framework of the complex- coordinate rotation method. The resonance energies and widths for this system having infinite, finite proton and deuteron, nuclear masses are reported. The resonance energies and widths are in excellent agreement with the experimental results. The isotope shift of the 1De resonance of H− and D−, measured from the respective ground state, is also compared with experimental determination.