Relativistic effects on the photoionization of hydrogen-like ions in plasmas

Abstract

In this study, the photoionization cross sections of C<sup>5+</sup>, Al<sup>12+</sup>, and W<sup>73+</sup> ions in a Debye plasma environment were calculated under the dipole approximation. The main emphasis was placed on investigating the influence of relativistic effects on shape resonances, Cooper minima, and virtual state effects. The relativistic effects lead to fine-structure splittings, allowing for the appearance of double shape resonance peaks in the total cross section. As the resonance peak widths and energy positions are influenced by the proximity to the critical screening length, the increasing nuclear charge Z results in significant differences in the magnitudes, widths, and positions of the double shape resonance peaks. The energy position of Cooper minima in the photoelectrons is related to the critical screening length corresponding to the final continuum state. Unlike the deeper minima observed in the total photoionization cross sections for C<sup>5+</sup> and Al<sup>12+</sup> ions, for the higher nuclear charge of W<sup>73+</sup> ions, the significant fine-structure splitting arising from relativistic effects results in substantial differences in the positions of the Cooper minima in the partial cross-sections. As a result, these minima appear shallower when superimposed in the total cross section. The screening length associated with the virtual state effect in W<sup>73+</sup> ions, which have a higher nuclear charge, is completely different from that of C<sup>5+</sup> and Al<sup>12+</sup> ions. Moreover, for the same screening length, there are significant differences in the magnitude of the virtual state enhancement in the low-energy region between C<sup>5+</sup> and Al<sup>12+</sup> ions.