The effects of dense semi-classical plasma (DSCP) on the ground state of the negative ion of hydrogen (H−) and on the dynamics of electron–hydrogen scattering have been investigated. DSCP is described by an effective potential which takes care of the collective effects of the plasma at large distances as well as the quantum mechanical effects of diffraction at small distances. An elaborative wave function is employed in the Rayleigh–Ritz variational method to compute the ground state energy of H− for various values of the plasma parameters. In particular, critical values of the plasma parameters are calculated accurately to make a detailed study on the stability of the ion embedded in DSCP. Furthermore, parameters related to the ground state of H− and H are used in the effective range theory to study the effects of DSCP on the dynamics of low-energy e − H(1s) scattering. Special emphasis is given to investigate the phenomenon of zero-energy resonances by computing the singlet scattering length near the critical values of the plasma parameters.

The effects of quantum plasmas (QP) on the S-wave resonance states of the positron-hydrogen system have been investigated by using the stabilization method. An effective potential, in the form of exponential cosine screened Coulomb potential, is used to describe the interactions among the charged particles in QPs. A number of S-wave resonance states associated with different thresholds of s-states of hydrogen atom [H(ns)] and s-states of positronium atom [Ps(ns)] are reported. For plasma-free cases, our results agree well with the results of other reliable calculations. Moreover, an in-depth study has been made to investigate the changes produced in the energy Er and width Γ of those states due to varying screening strength of QP. Our present results of energy and width of the positron-hydrogen system under QP associated with the higher-lying thresholds of hydrogen (H) and positronium (Ps) are reported for the first time in the literature.

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In this paper, the effects of plasmas on the S-wave resonance states in the positron-potassium system are investigated. Two different plasma conditions are considered, namely weakly coupled classical plasma (WCCP) and dense quantum plasma (DQP). The effective interaction potential in WCCP and DQP has been described by the Debye–Hückel model (static screened Coulomb potential) and a modified version of Debye–Hückel model (exponential cosine screened potential). Resonance parameters are determined by calculating the energy-density within the framework of the stabilization method. For the plasma-free case, three states, lying below the Ps[Formula: see text] threshold, are identified. The energy and the width agree well with the existing results in the literature. A detailed study is carried out to explore the changes emerging in the resonance parameters due to screening effects of WCCP and DQP. It is found that the energies of the three states are gradually pushed toward the Ps[Formula: see text] threshold due to the increasing plasma screening strength, whereas widths of the states vary differently.