Eur. Phys. J. D (2012) 66: 43
https://doi.org/10.1140/epjd/e2011-20660-7

Regular Article

Effect of strongly coupled plasma on the doubly excited states of heliumlike ions

¹ Department of Physics, Narula Institute of Technology, Agarpara, 700109 Kolkata, West Bengal, India
² Department of Physics, Ramakrishna Mission Vivekananda University, Belur Math, Howrah, 711202 West Bengal, India
³ Department of Mathematics, Visva Bharati, Santiniketan, 731235 West Bengal, India
⁴ Institute fur Physik, Universitat Kassel, 34109 Kassel, Germany

^a e-mail: profpkmukherjee@gmail.com

Received: 15 November 2011
Published online: 24 February 2012

Abstract

The effect of strongly coupled plasma occurring in astrophysical context has been studied for the first time to estimate the energy levels of the autoionizing states of highly stripped astrophysically important ions Al¹¹⁺, Si¹²⁺, P¹³⁺, S¹⁴⁺ and Cl¹⁵⁺ and also C⁴⁺ isoelectronic to helium. The transition energies corresponding to 1s²:¹S^e → 2s²:¹S^e, 2p²:¹D^e, 2s2p:¹P^o, 2s3d:¹D^e and 2p3d:¹F^o are analyzed with respect to different plasma densities using the ion sphere (IS) model of strongly coupled plasma. Transition energies are obtained from the position of the poles of a variational functional based on frequency dependent perturbation calculation probing the collective oscillation modes of the plasma embedded two electron ions. For the free ions corresponding to zero plasma coupling our calculated data agree well with those obtained from spectroscopic data while for the plasma embedded ions the data are new but follow systematic trend. The work has been performed in the domain of linear response theory. The analytical wave function of the doubly excited states have been obtained and may be useful for calculating various transition properties of the plasma embedded ions and also for estimating the rate coefficients for dielectronic recombination processes which play a major role in maintaining equilibrium in high temperature astrophysical or laser produced plasmas.