Differences in postcollision interaction (PCI) effects on Kr L 3 M 4;5 M 4;5 Auger electron spectra were observed, depending on whether the initial photoionization occurred slightly above the K threshold or slightly above the L 3 threshold. For the former, KL fluorescence emission most likely happens and then Auger processes due to the L 3 hole follow. The time delay due to fluorescence causes a reduced shift of the Auger peak and tailing toward lower energy, since the Auger overtaking of the photoelectron happens later in time and at a location farther away from the ionic core, compared to the case for the simple one-step L 3 M 4;5 M 4;5 Auger decay after L-shell photoionization. Time-dependent theory for PCI in multistep processes agrees well with experiment, illustrating the effect as an internal clock for the time-sequence of the dynamical process.

State-of-the-art Argon KLL Auger spectra measured using photon energies of hν = 3216 eV and 3400 eV are presented along with an Ar [1s] photoelectron spectrum (squared brackets indicate holes in the respective orbital). The two different photon energies used for measuring the Auger spectra allow distinguishing between the shake transitions during the Auger decay and the Auger transitions of the photoelectron satellites. A complete assignment of satellite transitions is provided, partially baseed on configuration interaction calculations. In addition, Artransitions are observed, which can be explained by knock-down transitions leading to a direct exchange of angular momenta between the excited electron and the Auger electron. The lifetime broadenings of the Ar [2s] single core-hole state and the [2s 2 ] as well as [2s2p] double core-hole states are also determined, confirming previously observed trends for double core-hole states.

An unexpectedly prominent angular momentum exchange effect in the double photoionization continuum was identified through the photoelectron recapture process induced by post-collision interaction (PCI). The Kr (M5N2,3N2,3) Auger electron spectrum originating from 3d−15/2 photoionization was measured with the photon energy tuned very close above the ionization threshold. As the photon energy approached the 3d−15/2 photoionization threshold, Rydberg series structures including several angular momentum components were formed within the Auger peak profile by the recapture of the photoelectrons into high-lying final ion orbitals. Our spectrum with line-width much narrower than the lifetime width of the corresponding core excited state allowed us to resolve detailed structures due to the orbital angular momentum states very clearly. Unexpectedly, conjugate peaks originating from the exchange of angular momentum between the photoelectron and the Auger electron through PCI were found to dominate the spectrum. Comparison with valence photoelectron spectrum of Kr via direct photoionization confirms the new assignment. Conjugate peaks were also found to be in accord with the quantum defect values obtained for the high Rydberg series Kr+4p−2(1S0, 1D2)ml. Extension of the new assignments to photon energies below threshold may call for the revision of previous interpretations of resonance Auger processes.

The Fano resonance has been a familiar and important feature in atomic and molecular physics for more than half a century. Typically, the combination of a discrete state with one or more continua results in an asymmetric peak in the ionization spectrum. The peak-shape, called the Fano profile, can be expressed by a simple formula derived by Fano in 1935. However, the interpretation of its characteristic parameter q, which represents the asymmetry of the peak in the formula, is not necessarily intuitively transparent. The Fano resonance is not necessarily a quantum effect, but it is a manifestation of a certain physical mechanism in various systems, both quantum and classical. Through the derivation of q from the known classical pictures with the classical coupled oscillator, we interpret the q value with a geometrical view. And further, we introduce a complex valued q parameter for the description of the resonance with a damped oscillator.