DOUBLE-AUTOIONIZATION DECAY OF RESONANTLY EXCITED SINGLE-ELECTRON STATES

Perturbation theory in the lowest non-vanishing order in interelectron interaction has been applied to the theoretical investigation of doub le-ionization decays of resonantly excited single-electron states. The formulae for the transition probabilities were derived in the LS coup ling scheme, and the orbital angular momentum and spin selection rules were obtained. In addition to the formulae, which are exact in this o rder, three approximate expressions, which correspond to illustrative model mechanisms of the transition, were derived as limiting cases of the exact ones. Numerical results were obtained for the decay of the r esonantly excited Kr I 3d(-1)5p[1P] state which demonstrated quite cle arly the important role of the interelectron interaction in double-ion ization processes. On the other hand, the results obtained show that l ow-energy electrons can appear in the photoelectron spectrum below the ionization threshold of the 3d shell. As a function of the photon fre quency, the yield of these low-energy electrons is strongly amplified by the resonant transition of the 3d electron to 5p (or to other discr ete levels), acting as an intermediate state, when the photon frequenc y approaches that of the transition.