XVIth International Workshop on Quantum Systems in Chemistry and Physics 

Abstract 
Effect of Confinement on the Resonance States of Atomic Systems 
J.K.Saha^{1}, T.K.Mukherjee^{1}, P. K. Mukherjee^{2,3} and B. Fricke^{4}
^{1}Narula Institute of Technology, Agarpara, Kolkata 700109, India
^{2}Department of Physics, Ramakrishna Mission Vivekananda University, Belur Math, Howrah, West Bengal 711202, India
and
^{3}Department of Mathematics, Visva Bharati University, Santiniketan, West Bengal 731 235, India
^{4}Institut fur Physik, Universitat Kassel, 34109 Kassel, Germany 
Effect of confinement on the resonance states of atomic systems, particularly for the two electron systems of different symmetries has been analysed using different theoretical methods. The type of confinement generated here is due to plasma background of different coupling strengths which lie in the domain of weak and strong coupling cases. The excited states studied here lie above the one electron continuum of the atomic systems and are doubly excited. These states lie under the energy levels corresponding to principal quantum number n>1 of the corresponding parent ion and are, in general, autoionising. For the weakly coupled plasma the Debye screening model and for the strongly coupled plasma Ion Sphere (IS) model have been used for such studies. The effect of such a confinement is to alter the potential under which the electons in the atomic system move. Schrodinger equation appropriate in such cases have been solved to obtain the ground and the doubly excited states. The plasma coupling strengths used here are such that a wide variety of plasma conditions envisaged by different temperature and number density of the plasma observed in laboratory and astrophysical context can be simulated. A number of isoelectronic ions of helium e.g. C^{4+}, Al^{11+}, Si^{12+}, P^{13+}, S^{14+}, Cl^{15+} which are of astrophysical importance have been chosen for detailed investigations using the Debye and the IS model of the plasma for the doubly excited energy levels 1s^{2}: ^{1}S^{e}> 2s^{2}:^{1}S^{e}; 2p^{2}:^{1}D^{e}, 2s2p:^{1}P^{o}, 2s3d:^{1}D^{e} and 2p3d:^{1}F^{o}. Appropriate spatial boundary conditions have been applied on the wavefunctions whenever necessary. Highly correlated calculations using Hylleraas basis sets have also been performed on He, Li^{+} and Be^{2+} on the doubly excited 2pnp:^{1,3}P^{e} and 2pnd:^{1,3}D^{e} states with n going up to 8 using Debye model of the plasma. Such data have been used for the study of transition wavelengths in appropriate cases. The general behavioural pattern of the doubly excited states under such plasma conditions has been analysed in detail. 

