Plasma-assisted photoionization of endohedrally confined hydrogen and argon

Abstract

Photoionization of hydrogen and argon atoms is investigated under the simultaneous influence of endohedral confinement and Debye plasma screening. Confinement is modeled using a Gaussian annular square well potential representing a diffusive fullerene cage, while plasma effects are introduced through static Debye–Hückel screening of the atomic core. Bound and continuum states are obtained by solving the radial Schrödinger equation within a single-active-electron framework, including spin–orbit coupling to resolve the argon 3p fine structure. Photoionization cross sections are calculated in the electric dipole approximation using energy-normalized continuum wavefunctions and channel-resolved analysis. In hydrogen, tuning the screening strength drives critical behavior near threshold, leading to quasibound and virtual-state-induced enhancements. In argon, interchannel competition and spin–orbit coupling produce pronounced near-threshold shape resonances governed primarily by the ϵd continuum channels. The 3p Cooper minimum exhibits systematic shifts with increasing screening strength, reflecting modifications to the radial dipole matrix element arising from changes in continuum phase accumulation and effective potential structure.