Fluorescence Time Delay in Multistep Auger Decay as an Internal Clock

Abstract

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.

Manifestation of postcollision interaction in Krypton LMN Auger spectra following K -shell photoionization

“…The Z+1 term value is consistent with the analysis of the Kr x-ray absorption spectrum [22] and with the Kr 3d −1 np Rydberg series recorded in high-resolution electron impact measurements [27]. With this procedure, we located the position of the Kr 1s ionization threshold (14327.19 (13) eV [24]), and therefore the excess energies, with an accuracy of better than 50 meV.…”

“…( 1) has recently been studied in Ref. [13]. In this work the Auger transition L 3 − M 4,5 M 4,5 has been investigated instead of the L 2 − M 4,5 N 2,3 Auger transition considered in the present paper.…”

“…One of the goals of Ref. [13] was to compare PCI effects recorded above the L 3 -edge but below the K -edge, where one-step Auger decay from the L 3 -vacancy state occurs, to PCI effects recorded above the K -edge where a time delay due to KL 3 fluorescence plays a role. Differences in the line shapes for the two cases were observed, and a theoretical model was proposed that explains the measured PCI-distorted line shapes.…”

“…The PCI distortion of the emitted LM M Auger electron spectra for the same case of Ar 1s photoionization followed by CRAD processes has been studied in noncoincidence measurements [12]. The CRAD process was also investigated in PCI distortion of the L 3 − M 4,5 M 4,5 Auger line following Kr 1s photoionization for a few values of excess photon energy above the threshold [13].…”

Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020

“…Differences in PCI effects on Kr L M 4,5 M 4,5 Auger electron spectra were recently published. [357] The PCI Auger shift depends on whether the initial photoionisation occurs slightly above the K threshold or slightly above the L 3 threshold. Above the K shell, Kα fluorescence emission followed by Auger processes due to the L 3 core hole takes place.…”