Cooper-type minima in quadrupole photoionization of plasma-embedded hydrogen atoms

The quadrupole photoionization of hydrogen atoms under the perturbation of plasma screening effects is investigated by the complex-coordinate rotation method. The Debye-Huckel (DH) and modified-DH potentials are adopted for describing the different features of plasmas. Comparisons of the quadrupole photoionization cross sections for these two screened potentials are made. The variation of cross sections with various Debye screening lengths is presented for illustrating the appearance of Cooper-type minima and shape resonances induced by plasma screening. The relations between the Cooper-type minima and the instability of the initial bound states are discussed.