Low Energy Photoionization in the Ar Isoelectronic Sequence: Complex Effects of Z
Valence 3p photoionization of neutral Ar and several ions isoelectronic to it is investigated in the low photon-energy regime using the relativistic-random-phase approximation. With increasing Z, a steady shift of “Cooper minimum” towards the ionization threshold is seen in the cross section such that at sufficiently high Z it crosses the threshold to enter the discrete of 3p channel. Further, a remarkable threshold feature is observed for some ions that essentially originates from strong Z-dependent interaction with inner 3s photoexcitation series. Results strengthen our previous caution against any indiscriminate interpolation (or extrapolation) of ionic data at low energies.
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