Atomic structure considerations for the low-temperature opacity of Xenon

Abstract

Here, we have begun a preliminary investigation into the opacity of Xe at low temperatures (<50 eV). The emissivity and opacity of Xe is a crucial factor in determining the utility of Xe in EUV lithography, with numerous industrial applications. To this end, we have been exploring the accuracy of some approximations used in opacity models for the relevant ion stages of Xe (6 times ionized through 20 times ionized). Due to the complexity of Xe atomic structure, one needs to use full configuration-interaction to properly describe the strong mixing in the various n=4 sub-shells that give rise to the Δn=0 and Δn=1 transitions that dominate the opacity spectrum at low temperatures. Since calculations that include full configuration-interaction for large numbers of configurations quickly become computationally prohibitive, we have explored hybrid calculations, in which full configuration-interaction is retained for the most important transitions, while intermediate coupling is employed for all other transitions. After verifying atomic structure properties, local-thermodynamic-equilibrium (LTE) opacities are generated using the ATOMIC code at selected temperatures and densities and compared to various experimental results.