Theoretical Atomic Collisions Laboratory

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We have investigated the effect of weakly coupled hot plasmas on the dipole polarizabilities of positronium negative ion and hydrogen negative ion. The plasma effect is taken care of by employing a screened Coulomb (Yukawa) potential of Debye type, and highly correlated exponential wave functions are used. Dipole polarizabilities for various screening parameters are reported.

The Van der Waals two-body dispersion coefficients for interactions between the positronium (Ps) atom and light atoms have been investigated using highly correlated exponential basis functions in the framework of both pure Coulomb and screened Coulomb potentials. The C6, \{C8\} and \{C10\} coefficients for Ps–Ps and Ps–H interactions, and the \{C6\} coefficients for Ps–He interactions for both the screened and unscreened cases, are reported.

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We have investigated the doubly excited 1,3 P o resonance states of helium embedded in weakly coupled plasmas. A screened Coulomb potential obtained from the Debye model is used to represent the interaction between the charge particles. A correlated wavefunction consisting of a generalized exponential expansion has been used to represent the correlation effect. A total of 18 resonances (9 each for 1 P o and 3 P o states) below the n = 2 He + thresholds has been estimated by calculating the density of states using a stabilization method. For each spin state, this includes four members in the 2s n p + (2 ≤ n ≤ 5) series, three members in the 2s n p − (3 ≤ n ≤ 5) series, and two members from 2p n d( n = 3, 4) series. The resonance energies and widths for various Debye parameters ranging from infinity to a small value for these 1,3 P o resonance states are reported. In addition, the wavelengths for the photo-absorption of a helium atom from its ground state to such 1 P o resonance states for different Debye lengths are also reported.