Multi-electron Coincidence Method Research Articles

Auger cascade initiated by the Coster–Kronig transition from the Kr 3p core-hole states

The full Auger cascade initiated by the M2,3M4,5N Coster–Kronig (CK) transitions from the Kr 3p core-hole states is revealed by using a multi-electron coincidence method. The individual CK transitions are located on the basis of the energy correlations between the Auger electrons emitted in the CK and secondary Auger transitions. The decay processes of the CK-final Kr2+ states are investigated, whereby two-electron emissions leading to the formation of Kr4+ levels are identified.

Super-Coster-Kronig decay of Kr 3p core-hole states studied by multielectron coincidence spectroscopy

Super Coster-Kronig (SCK) decay following Kr $3p$ photoionization has been investigated using a multielectron coincidence method. It is found that the SCK pathway occupies 23% of the $3{p}_{1/2}$ decay and only 2.5% of the $3{p}_{3/2}$ decay. The significant difference between the two $3p$ spin-orbit levels mainly results from the difference in energetics: almost all SCK transitions are energetically allowed in the $3{p}_{1/2}$ decay but only SCK transitions to the $^{3}F$ levels of $3{d}^{\ensuremath{-}2}$ are possible in the $3{p}_{3/2}$ decay. Subsequent decay processes from the SCK-final $3{d}^{\ensuremath{-}2}$ states are investigated, where a maximum of fivefold electron coincidences are analyzed.

Single and multiple Auger decay processes from the Ne+1s−12p−1np shake-up states studied with a multielectron coincidence method

The single, double, and triple Auger decay processes from the $1{s}^{\ensuremath{-}1}2{p}^{\ensuremath{-}1}np$ shake-up states of Ne have been studied with a multielectron coincidence method. It is revealed that the Rydberg electron promoted in the initial photoionization step generally acts as a spectator both in the single and double Auger decays. The single Auger decay predominantly produces three-hole one-particle final states while leaving the Rydberg electron virtually unchanged. In the cascade double Auger paths, the Rydberg electron is a spectator in the first step of the cascade process but is subsequently released in the second step, leading to the formation of three-hole final states. The direct paths of double Auger decays, which are much weaker than the cascade paths, produce preferably four-hole one-particle states due to the spectator behavior of the Rydberg electron. The distributions of the $\mathrm{N}{\mathrm{e}}^{4+}$ states populated by the triple Auger decays are also presented.

Single, double, and triple Auger decays from 1s shake-up states of the oxygen molecule.

The single, double, and triple Auger decays from the 1s shake-up states of O2 have been studied using a multi-electron coincidence method. Efficient populations of two-hole final states are observed in single Auger decays of the π-π* shake-up states, which is understood as a characteristic property of the Auger transitions from shake-up states of an open-shell molecule. The O23+ populations formed by double Auger decays show similar profiles for both the O1s-1 and shake-up states, which is due to the contributions from cascade double Auger processes. While the cascade contributions to the double Auger decays increase with the initial shake-up energy, the probability of direct double Auger processes remains unchanged between the O1s-1 and shake-up states, which implies a weak influence of the excited electron on the double Auger emission that originates from the electron correlation effect.

Multiple Auger decay of the neon1s-core-hole state studied by multielectron coincidence spectroscopy

The Auger decay processes from the $1s$-core-hole state of Ne have been investigated with a multielectron coincidence method. We have observed the double and triple Auger decays, in which both cascade and direct processes are identified from different ways in energy sharing between the Auger electrons. Branching ratios for the different electronic configurations of the Auger final states are determined from the corresponding electron coincidence yields. Particularly for the double Auger decay, the branching ratios are divided into the individual contributions from direct and cascade paths.

Resonant multiple Auger decay after the2p3/2−14sexcitation in Ar studied with a multielectron coincidence method

The multiple Auger electron emission processes after the $2{p}_{3/2}^{\ensuremath{-}1}$ 4$s$ excitation in Ar have been investigated with a multielectron coincidence method. We have observed the double, triple, and quadruple Auger decays of the resonant state, where both cascade and direct processes are identified. The cascade processes in the resonant double and triple Auger decays result mostly from the spectator behavior of the Rydberg electron in the initial core-hole decay: First Auger decay produces ion states with large internal energies, and subsequent electron emission leads mainly formation of ground Ar${}^{2+}$ and Ar${}^{3+}$ states. It is revealed that spectator behavior, which is known to be the dominant path in resonant single Auger decay, is also important in the direct paths of the resonant double and triple Auger decays. In contrast, the participation of the Rydberg electron is predominant in the direct path of the resonant quadruple Auger decay.

Electron reemission processes following photoelectron recapture due to post-collision interaction in inner-shell photoionization of water molecules

Electron reemission following photoelectron recapture due to post-collision interaction has been studied at 0.7 eV the inner-shell photoionization threshold of water molecules, using a multi-electron coincidence method. Electron reemissions after single Auger decay occur from O and OH fragments which are produced by the dissociations of high-n Rydberg H2O(+) states populated through photoelectron recapture. In addition, electron reemissions after double Auger decay are identified in triple coincidence events, where autoionization lines from O and O(+) fragments are observed.

Auger decay of molecular double core-hole and its satellite states: Comparison of experiment and calculation

Auger decay of the C(2)H(2) double core-hole (DCH) states, including the single-site DCH (C1s(-2)), two-site DCH (C1s(-1)C1s(-1)), and satellite (C1s(-2)π(-1)π∗(+1)) states, has been investigated experimentally using synchrotron radiation combined with multi-electron coincidence method, and theoretically with the assumption of the two-step sequential model for Auger decay of the DCH states. The theoretical calculations can reproduce the experimental two-dimensional Auger spectra of the C(2)H(2) single-site DCH and satellite decays, and allow to assign the peaks appearing in the spectra in terms of sequential two-electron vacancy creations in the occupied valence orbitals. In case of the one-dimensional Auger spectrum of the C(2)H(2) two-site DCH decay, the experimental and calculated results agree well, but assignment of peaks is difficult because the first and second Auger components overlap each other. The theoretical calculations on the Auger decay of the N(2) single-site DCH state, approximately considering the effect of nuclear motion, suggest that the nuclear motion, together with the highly repulsive potential energy curves of the final states, makes an important effect on the energy distribution of the Auger electrons emitted in the second Auger decay.

Communication: Formation of slow electrons in the Auger decay of core-ionized water molecules

Double Auger decay of O1s(-1) and its satellite states in H(2)O has been studied with a multi-electron coincidence method, and a process leading to autoionizing O* fragments has been revealed. The breaking of the two O-H bonds producing the autoionizing O* fragments occurs for highly excited H(2)O(2+) populated by the initial Auger decay. The O* fragments are more favorably produced in the decay from the satellite states, resulting from the larger population of highly excited H(2)O(2+) states inheriting the valence excitation in the initial state.

Influence of double Auger decay on low-energy 3dphotoelectrons of krypton

Effects of postcollision interaction (PCI) observable in low-energy 3$d$ photoelectron spectra of Kr, which are associated with double Auger decay of the created inner-shell vacancy, are investigated by a combined experimental and theoretical approach. Measurements are based on an efficient multielectron coincidence method. Calculations have been carried out in the framework of a semiclassical approach. Our investigation reveals strong PCI distortion of the photoelectron line shapes, which depends on the kinematics of the process and the characteristics of the double Auger decay.

Energy Correlation among Three Photoelectrons Emitted in Core-Valence-Valence Triple Photoionization of Ne

The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s 2s2 2p4 configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons.

Two-electron emissions on atomic photoabsorption studied by multi-electron coincidence spectroscopy

Simultaneous two-electron emissions from core-valence double photoionization in Ne and upon core-electron excitation in Ar have been studied using a very efficient multi-electron coincidence method. The former case demonstrates that the population ratio of singlet and triplet doubly-charged ion states reveals the double photoionization dynamics. The latter case shows that a weakly-bound electron can be used as a probe of the double Auger dynamics of a core-hole. In both cases, the inadequacy of the shake-off model is revealed by the experimental observations alone and the necessity to describe better electron correlation for two-electron emission, as done in the knock-out model.

Probing the mechanism of simultaneous two-electron emission on core-hole decay

Simultaneous two-electron emission upon $2p$ core-electron excitation in Ar has been studied using a state-of-the-art multielectron coincidence method. Simultaneous two-electron emission effectively populates Rydberg-excited ${\text{Ar}}^{2+}$ states, in which the excited electron behaves as a spectator of the direct double Auger decay of the core hole. This observation constitutes experimental evidence that the shake-off mechanism is not sufficient to model direct double Auger decay of a $2p$ hole in Ar and suggests an important contribution from the knock-out mechanism.

Auger decays of 1s shake-up and shake-off states in N2 molecules

We have studied Auger decays of the 1s shake-up and shake-off states in N2 molecules with a state-of-the-art multi-electron coincidence method. The multi-electron coincidences reveal overall features of the Auger transitions from the individual core-hole states. The decay features of the shake-up states are interpreted by spectator and participant roles of the exited electrons. It is observed that the valence holes formed at the initial shake-off process remain unchanged during the Auger decay from the shake-off states.

Single, double, and triple Auger decay of the Xe4pcore-hole states

Auger decay of ${\mathrm{Xe}}^{+}$ states arising from $4p$ ionization has been studied with a very efficient multielectron coincidence method. Coster-Kronig decay from ${\mathrm{Xe}}^{+}$ $4{p}^{\ensuremath{-}1}$ and the subsequent decay into ${\mathrm{Xe}}^{3+}$ states with three valence holes are identified. Formation of ${\mathrm{Xe}}^{4+}$ is also observed as quadruple coincidences between a $4p$ photoelectron and three Auger electrons. The relative probabilities of individual multi-ionization processes are determined from the coincidence yields.

Multielectron coincidence spectroscopy for core-valence doubly ionized states of CO

Double photoionization into states which have holes in one core and one valence orbitals has been observed in CO using a state-of-the-art multielectron coincidence method. The core-valence CO2+ structures exhibited on the electron coincidence spectra are assigned by comparison with the available calculation [H. Schulte et al., J. Chem. Phys. 105, 11108 (1996)]. Features of the spectrum confirm that the properties of the CO2+ states are characterized by the interaction between the localized valence holes and the core holes.

Auger decay of Ne 1s photoionization satellites studied by a multi-electron coincidence method

The Auger decay of Ne 1s photoionization satellite states is studied with a magnetic-bottle multi-electron coincidence method. The energy correlations among the multi-electrons associated with the double Auger decay from the Ne+ satellite states are extracted from the accumulated coincidence dataset. It is concluded that the Ne2+ states populated through the initial Auger decays from the Ne+ satellite states can be excited states that lie above the Ne3+ threshold. Their subsequent decay produces slow electrons in the 0–25 eV kinetic energy range. Possible assignments of the intermediate Ne2+ and the final Ne3+ states are given.