Central-field calculations of photoionisation cross sections of excited states of Rb and Sr⁺and analysis of photoionisation cross sections of excited alkali atoms using quantum defect theory

Photoionisation cross sections for excited nl states (n<or=20, l<or=4) of Rb and Sr + have been computed in the framework of a single-electron model by the use of a central potential. The evolution of non-hydrogenic behaviour of photoionisation near threshold is studied along a given series. Moreover, isoelectronic variations from Rb to Sr + as well as systematic trends along the sequence of alkali atoms Li through Cs are discussed. The non-hydrogenic traits, mainly the occurrence of minima in photoionisation cross sections, are analysed in terms of quantum defect theory.