62 research outputs found
HySIA: Tool for Simulating and Monitoring Hybrid Automata Based on Interval Analysis
We present HySIA: a reliable runtime verification tool for nonlinear hybrid
automata (HA) and signal temporal logic (STL) properties. HySIA simulates an HA
with interval analysis techniques so that a trajectory is enclosed sharply
within a set of intervals. Then, HySIA computes whether the simulated
trajectory satisfies a given STL property; the computation is performed again
with interval analysis to achieve reliability. Simulation and verification
using HySIA are demonstrated through several example HA and STL formulas.Comment: Appeared in RV'17; the final publication is available at Springe
Simulation of Auger decay dynamics in the hard X-ray regime: HCl as a showcase
Auger decay after photoexcitation or photoemission of an electron from a deep inner shell in the hard X-ray regime can be rather complex, implying a multitude of phenomena such as multiple-step cascades, post-collision interaction (PCI), and electronic state-lifetime interference. Furthermore, in a molecule nuclear motion can also be triggered. Here we discuss a comprehensive theoretical method which allows us to analyze in great detail Auger spectra measured around an inner-shell ionization threshold. HCl photoexcited or photoionized around the deep Cl 1s threshold is chosen as a showcase. Our method allows calculating Auger cross sections considering the nature of the ground, intermediate and final states (bound or dissociative), and the evolution of the relaxation process, including both electron and nuclear dynamics. In particular, we show that we can understand and reproduce a so-called experimental 2D-map, consisting of a series of resonant Auger spectra measured at different photon energies, therefore obtaining a detailed picture of all above-mentioned dynamical phenomena at once
Postcollision interaction effects in KLL Auger spectra following argon 1s photoionization
Postcollision interaction effects on the Auger decay of a deep core hole are
studied both experimentally and theoretically. KL2,3L2,3 decay spectra of the
Ar 1s vacancy are measured with high-energy resolution with excess photon
energies ranging from 0 to 200 eV above the ionization threshold. Interaction
of the Auger electron with the photoelectron and the ion field manifests
itself in the Auger spectra as a distortion of the energy distribution of the
Auger electron close to threshold. Moreover, recapture of the photoelectron
due to energy exchange is dominating in the low-photon-energy range above
threshold. The experimental results are compared with calculations based on
the semiclassical approach to the postcollision interaction. The energies of
the discrete levels and individual recapture cross sections are computed in
the Hartree-Fock approximation. Good agreement is found between the calculated
and experimental spectra, validating the model used
Ultrafast nuclear dynamics in the doubly-core-ionized water molecule observed via Auger spectroscopy
We present a combined experimental and theoretical study of the Auger-emission spectrum following double core ionization and excitation of gas-phase water molecules with hard-x-ray synchrotron radiation above the O Kâ2 threshold. We observe an indication of ultrafast proton motion occurring within the 1.5 fs lifetime of the double-core-hole (DCH) states in water. Furthermore, we have identified symmetric and antisymmetric dissociation modes characteristic for particular DCH states. Our results serve as a fundamental reference for state-of-the-art studies of DCH dynamic processes in liquid water both at synchrotron and free-electron-laser facilities
Two-to-one Auger decay of a double L vacancy in argon
We have observed L223âM3 Auger decay in argon where a double vacancy is filled
by two valence electrons and a single electron is ejected from the atom. A
well-resolved spectrum of these two-to-one electron transitions is compared to
the result of the second-order perturbation theory and its decay branching
ratio is determined
Subfemtosecond Control of Molecular Fragmentation by Hard X-Ray Photons
Tuning hard x-ray excitation energy along Cl 1sâÏâ resonance in gaseous HCl
allows manipulating molecular fragmentation in the course of the induced
multistep ultrafast dissociation. The observations are supported by
theoretical modeling, which shows a strong interplay between the topology of
the potential energy curves, involved in the Auger cascades, and the so-called
core-hole clock, which determines the time spent by the system in the very
first step. The asymmetric profile of the fragmentation ratios reflects
different dynamics of nuclear wave packets dependent on the photon energy
Single and multiple excitations in double-core-hole states of free water molecules
We present a combined experimental and theoretical study of the double-core-hole photoelectron spectrum obtained in isolated water molecules irradiated with hard x-rays above the oxygen Kâ2 threshold. States of the type O Kâ2V and multiply excited states are created by single-photon absorption and subsequent one-electron emission. A detailed analysis enabled by high experimental resolution reveals dissociative nuclear dynamics in the Kâ2V pre-edge states. At the binding energies above the Kâ2 double-ionization potential, a complex spectral pattern is observed and attributed to highly excited states involving multiple shake-up excitation processes with the aid of state-of-the-art theoretical calculations. A strong broadening due to the nuclear motion indicates a highly dissociative nature of these multiply excited states, in agreement with the theoretical analysis
Auger resonant-Raman decay after Xe L-edge photoexcitation
We have investigated resonant Auger decay of xenon following photoexcitation
of each of the three L edges under resonant-Raman conditions, which allowed us
to characterize several higher Rydberg transitions. Relative intensities for
spectator final states reached after L1â, L2â, and L3-edge excitations are
studied in detail. Thanks to state-of-the-art experimental arrangements, our
results not only reproduce the previously calculated 3dâ25d and nd(n>5) state
cross sections after L3 excitation, but also allow extracting the 3dâ26d
spectator state energy position and revealing its resonant behavior, blurred
by the insufficient experimental resolution in previous data sets. The 3dâ26p
and 3dâ27p states reached after L1 excitation as well as the 3dâ25d and 3dâ26d
states reached after L2 excitation are also investigated and their relative
intensities are reported and compared to ab initio Dirac-Hartree-Fock
configuration-interaction calculations. We found the signature of electronic-
state-lifetime interference effects between several coherently excited
intermediate states, due to large lifetime broadening. Electron recapture
processes are also identified above all three photoionization thresholds
Argon as a showcase
Electronic-stateâlifetime interference is a phenomenon specific for ionization
of atoms and molecules in the hard-x-ray regime. Using resonant KL2,3L2,3
Auger decay in argon as a showcase, we present a model that allows extracting
the interference terms directly from the cross sections of the final
electronic states. The analysis provides fundamental information on the
excitation and decay processes such as probabilities of various decay paths
and the values of the dipole matrix elements for transitions to the excited
states. Our results shed light on the interplay between spectator, shake-down,
and shake-up processes in the relaxation of deep core-hole states
Direct Observation of Double-Core-Hole Shake-Up States in Photoemission
Direct measurements of Ar+ 1sâ12pâ1nl double-core-hole shake-up states are
reported using conventional single-channel photoemission, offering a new and
relatively easy means to study such species. The high-quality results yield
accurate energies and lifetimes of the double-core-hole states. Their
photoemission spectrum also can be likened to 1s absorption of an exotic argon
ion with a 2p core vacancy, providing new information about the spectroscopy
of both this unusual ionic state as well as the neutral atom
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