Direct Double Auger Decay Research Articles

Effects of single-photon double photoionization and direct double Auger decay on K-shell ionization kinetics of Ar atoms interacting with XFEL pulses

In studies investigating the interaction of matter with ultraintense, ultrashort x-ray free electron laser (XFEL) pulses, the evolution kinetics are generally described by directly solving a time-dependent rate equation that considers single-photon and single-electron processes. In the present study, we show the effects of single-photon double photoionization and direct double Auger decay in the K-shell ionization kinetics of XFELs interaction with argon atoms. Because a huge number of coupled transition channels are present in the K-shell ionization, we develop a Monte Carlo method to simulate the complex ionization kinetic processes and give the level population evolution of ions and charge state distribution (CSD). The K-shell-dominated ionization dynamics of Ar irradiated by XFEL pulses with photon energies of 5000, 5500 and 6500 eV are investigated and compared with available experimental observations of the CSD. The results show that the population fractions of Ar5+, Ar6+ and Ar9+ are increased by 78%, 152% and 144%, respectively, by these higher-order processes at a photon energy of 5000 eV. Including the direct double-electron processes, the predicted CSDs are in better agreement with the experiments carried out at the photon energies of 5000, 5500 and 6500 eV. It is expected that the developed theoretical formalism can be used to more accurately calibrate the beam profile and intensity of XFELs.

Dominance of double processes in complete Auger decay of Rb+(3d−1)

The complete Auger decay of ${\mathrm{Rb}}^{+}(3{d}^{\ensuremath{-}1})$ including single and double processes is investigated using the distorted wave approximation. The direct double Auger decay was calculated by separating the knock-out and shake-off mechanisms. For single Auger decay of the $3{d}^{\ensuremath{-}1}$ hole state, it is generally believed that the dominant channels should be levels belonging to the configurations of $[1{s}^{2}2{s}^{2}2{p}^{6}3{s}^{2}3{p}^{6}3{d}^{10}]4{s}^{2}4{p}^{4}5s$, $4s4{p}^{5}5s$, and $4{s}^{0}4{p}^{6}5s$. Here we predict that the strongest channels originate from $4{s}^{2}4{p}^{3}4d5s$, which accounts for 36.3% of the single Auger decay rate. The levels belonging to this configuration can further decay to ${\mathrm{Rb}}^{3+}$, resulting in a large fraction of cascade double Auger decay. Moreover, the probability of direct double Auger decay in Rb is also high because of its $5s$ electron. The branching ratios of cascade and direct double Auger decay are predicted to be 50.60% and 22.13%, respectively, resulting in the dominance of double Auger decay with a fraction of 72.73% in the complete Auger decay of ${\mathrm{Rb}}^{+}(3{d}^{\ensuremath{-}1})$.

Auger decay including direct double processes of K-shell hollow states of Ne+ and the related hypersatellite radiative transitions

In this study, we theoretically investigated single and double Auger decay processes from the K−2V (V = 3s, 3p, 3d, 4s, 4p, 4d) hollow states of Ne+ in the framework of the first- and second-order perturbation theory implemented by the distorted wave approximation. The direct double Auger decay rates were calculated based on the separation of knock-out and shake-off mechanisms. Atomic data, including the transition energy, single and double Auger decay rates and natural lifetime width, are obtained and compared with the experimental and theoretical results available in the literature. The natural lifetime widths of the K−2V hollow states, including the contributions from single and direct double Auger decay, are in excellent agreement with a recent experiment. Using our theoretical results, we diagnosed the relative population fractions of the initial quantum states prepared in the experiment and interpreted the measured Auger spectra. There is an excellent agreement between the theoretical and experimental results. Finally, the hypersatellite Kα radiative transitions relevant to these hollow states were investigated using the natural lifetime widths determined by single and direct double Auger rates.

Single and double K-shell resonant photoionization and Auger decay of 1s → 2p excited states of O+–O4+

In this work, single and double photoionization cross sections in the vicinity of 1s → 2p resonances are investigated theoretically for quantum states belonging to the ground and first excited configurations of O+ –O4+ . R-matrix method has been employed to obtain the single ionization cross section, whereas the double ionization cross sections are obtained by the branching ratios of the direct double Auger decay to the total Auger decay. By analyzing possible double ionization pathways, we conclude that the double photoionization originates predominately from the direct double Auger decay of the K-shell resonant states. Our theoretical work diagnosed the population fraction of the quantum state prepared in a recent experiment and successfully interpreted the experimental observations on both single and double photoionization cross sections.

Single, double, and triple Auger decay probabilities ofC+(1s2s22p22D,2P)resonances

Single, double, and triple Auger decay rates of ${\mathrm{C}}^{+}(1s2{s}^{2}2{p}^{2}{\phantom{\rule{0.16em}{0ex}}}^{2}D,{\phantom{\rule{0.16em}{0ex}}}^{2}P)$ resonances were calculated in the framework of perturbation theory. The direct double Auger decay probabilities were calculated by using the approximate formulas according to the knockout and shakeoff mechanisms, in which the knockout mechanism was found to be dominant. Then the knockout mechanism was employed to investigate the complex triple Auger decay process, and the calculated rates have good agreement with the available experimental values.

Effects of Direct Double Auger Decay on the Population Dynamics of Neon Irradiated by Ultraintense x‐ray Pulses

AbstractThe population and charge state distribution of neon interacting with ultraintense x‐ray pulses are investigated by solving a time‐dependent rate equation in the detailed level‐accounting (DLA) approximation. Due to the detailed description of neon atom and ions, our DLA result improves the agreement between predictions and experimental measurements for odd neon charge states. In the framework of the DLA formalism, we further studied the effects of direct double Auger decay (DDAD) on charge state distribution. After the 1s photoionization of neon atom, the DDAD processes give accessible decay channels from the K‐shell hole state of Ne+ to levels of Ne3+, resulting in an increase of the population fraction of Ne3+ and a decrease of that of Ne2+. Compared with the results without considering the DDAD effects, better agreement is obtained between theory and experiment. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Auger decay and the direct double ionization probability of a 2p inner-shell hole in a singly charged Ar+ ion

Single and double Auger decay processes of Ar+ 2p −1 hole levels belonging to the configurations of 2p 53s 23p 5 and 2p 53s3p 6 are investigated in the framework of perturbation theory implemented by the distorted wave approximation. The single Auger decay channels and rates are determined and the predicted total rates can differ by more than an order of magnitude for the levels of 2p 53s 23p 5, yet they are very close for levels belonging to 2p 53s3p 6. By combining the double photoionization cross sections of the neutral species, our theoretical Auger spectra of the single Auger decay process nicely interpreted a recent experiment [S.M. Huttula et al., Phys. Rev. Lett. 110, 113002 (2013)]. A configuration averaged branching ratio of 6.5% and 7.3% are predicted for the direct double Auger decay to the total probability for 2p 53s 23p 5 and 2p 53s3p 6, respectively, which is smaller than that of Ar 2p −1 hole states.

Complete Auger decay pathways of Kr 3d−1 hole levels including direct double processes

The detailed level-to-level single and double Auger decay rates of Kr 3d−1 hole states are investigated in the framework of the first and second perturbation theory implemented by distorted wave approximation with the balanced large-scale configuration interaction of the successive ions being taken into account. The branching ratios of cascade and direct double Auger decay to the total probability are predicted to be 16.5% and 16.1%, respectively, for Kr and 16.8% and 17.2% for Kr , resulting in total double branching ratios of 32.6% and 34.0% for the two levels of Kr 3d−1 hole. A comparison is made with the available experimental results on the branching ratio into triply charged ions and good agreement was found with the most recent published work. This work represents the first theoretical study to correctly explain the experimental measurements. The complete pathways were depicted by including the direct double Auger decay process. Compared with the Auger decay of Ar 2p−1, the fraction of the cascade double of Kr 3d−1 is dramatically enhanced yet that of direct double Auger processes is only slightly increased.

Level-to-level and total probability for Auger decay including direct double processes of Ar2p−1hole states

Auger decay including direct double processes of Ar $2{p}^{\ensuremath{-}1}$ hole levels is investigated in the framework of perturbation theory implemented by distorted wave approximation with balanced large-scale configuration interaction among the successive ions being taken into account. The complex transition amplitude obtained from the second perturbation theory for the direct double Auger decay (DAD) is decomposed into approximate formulas according to two generally agreed mechanisms of shake-off and knock-out. Practical computations showed that the knock-out condition is fulfilled and thus justified such a decomposition treatment of knock-out mechanism. The contribution to the DAD probability from knock-out mechanism is larger than shake-off by an order of magnitude and therefore the former is dominant. The interference effect between the knock-out and shake-off mechanisms should be trivial and neglecting it we obtained a branching ratio of 12.0$%$ for the direct DAD into triply charged states of Ar${}^{3+}$. By including cascade double decay, a total branching ratio of 14.9$%$ is obtained. Our result explained recent experimental results on the branching ratio into triply charged ion, and should be useful for further detailed experimental investigations.

Unveiling residual molecular binding in triply charged Hydrogen Bromide

Double Auger decay following HBr(3d) inner-shell ionization by synchrotron radiation has been used to investigate HBr3+ potential energy curves. The direct double Auger decay reveals the residual binding energy sustained by theoretical calculation. Sequential processes are also observed and are characterized through observation of Br+* autoionizing states following HBr2+ fragmentation.

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.

Resonant double Auger decay in carbonK-shell excitation of CO

We have studied double Auger decay after C 1s→2 photoexcitation in gas phase carbon monoxide. Two distinct processes, namely direct double Auger decay and cascade double Auger decay, are identified and studied in detail using multiple coincidence techniques. Cascade Auger decay is shown to be the overall dominant process. Decay channels involving the dissociation of the molecule followed by autoionization of the oxygen fragments are observed.

Energy and angular distributions of electrons emitted by direct double auger decay.

We have observed the direct L(2,3)MMM double Auger transition after photoionization of the 2p shell of argon by angle-resolved electron-electron coincidence spectroscopy. The process is responsible for about 20% of the observed Auger electron intensity. In contrast to the normal Auger lines, the spectra in double Auger decay show a continuous intensity distribution. The energy and angular distributions of the emitted electrons allow one to obtain information on the electron correlations giving rise to the double Auger process as well as the symmetry of the associated two-electron continuum state.