On the threshold behaviour of bound-bound and bound-free photoabsorption for the screened Coulomb potentials

Computations of bound-bound and bound-free transition strengths for a particle bound by a screened Coulomb (Debye) potential show that near the ionization limit transition strengths differ markedly from hydrogenic values: oscillator strengths of Rydberg series diminish more rapidly than the hydrogenic n -3 decrement and photoionization cross sections are zero at threshold. Sharp near-threshold photoionization resonances occur for appropriate Debye lengths. This paper examines these effects and presents illustrative computations.