ELECTRONIC DECAY PROCESSES OF PHOTOEXCITED 2P RESONANCES OF ATOMIC AR, K, AND CA

An experimental and theoretical study is presented of the 2p --> ms, nd inner-shell excitations in the elements Ar, K, and Ca with special emphasis on the 2p --> 3d excitations. The present work is mainly concerned with investigations of K and Ca. An interpretation is given of the resonant Auger spectra in which it is shown that the difference in collapse of the 3d wave function in the presence of holes in the 2p shell compared to holes in the 3p shell leads to qualitative differences between the three atoms. In Ar, shake effects are very strong between the initial state with one 2p hole and the final state with two holes in the 3p shell due to the fact that the 3d orbital collapses between the two. However, in K and Ca the 3d orbital is collapsed in both states and shake effects are found to be much smaller for this excitation. In contrast, for K and Ca it is predicted that the 4d orbital will show strong shake effects. The collapse of the 3d orbital in the final state of all three atoms leads to resonant Auger spectra which are very different from those following direct ionization in the 2p shell. The details of the resonant Auger spectra depend on the degree of collapse; we discuss the differences in the observed spectra in terms of the relative strengths of the electrostatic 3p <-- --> 3p and 3p <-- --> 3d interactions in the three elements. The second-step Auger decays in K and Ca are studied both experimentally and theoretically.