Singly excited S-states of compressed two-electron ions

TL;DR

This paper investigates how spherical confinement affects the energy levels and structural properties of two-electron ions in S-states, revealing degeneracy, level-crossing, and destabilization phenomena through variational calculations.

Contribution

It provides a detailed variational analysis of confined two-electron ions, including energy estimates, degeneracy, and critical pressures for destabilization, which are novel insights into confined atomic systems.

Findings

Identification of incidental degeneracy and level-crossing phenomena.

Estimation of critical pressures for confinement-induced destabilization.

Analysis of energy level shifts under spherical confinement.

Abstract

A detailed analysis on the effect of spherical impenetrable confinement on the structural properties of two-electron ions in S-states have been done. The energy values of 1sns [n = 2-4] (3Se) states of helium-like ions (Z = 2-5) are estimated within the framework of Ritz variational method by using explicitly correlated Hylleraas-type basis sets. The correlated wave functions used here are consistent with the finite boundary conditions due to spherical confinement. A comparative study between the singlet and triplet states originating from a particular electronic configuration shows incidental degeneracy and the subsequent level-crossing phenomena. The thermodynamic pressure felt by the ion inside the sphere pushes the energy levels towards continuum. Critical pressures for the transition to strong confinement regime (where the singly excited two-electron energy levels cross the corresponding one-electron threshold) as well as for the complete destabilization are also estimated.