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New magnet design of a magnetic bottle electron spectrometer allowing the detection of multiply charged ions in coincidence with n electrons. Electrons spectra obtained without and with filtering by coincidence with Xen+ ions.

Single-photon multiple photoionization results from electron correlations that make this process possible beyond the independent electron approximation. To study this phenomenon experimentally, the detection in coincidence of all emitted electrons is the most direct approach. It provides the relative contribution of all possible multiple ionization processes, the energy distribution between electrons that can reveal simultaneous or sequential mechanisms, and, if possible, the angular correlations between electrons. In the present work, we present a new magnet design of our magnetic bottle electron spectrometer that allows the detection of multiply charged Xe

Single-site Double-Core Hole (ss-DCH or K

Synopsis The study of atomic multiple photoionization by a single photon can be performed by detecting in coincidence all the corresponding electrons with a magnetic bottle time of flight spectrometer. To reveal minor triple ionization channels of Xe atom that are hindered by radom coincidences, we have detected three electrons in coincidence with the corresponding Xe3+ ion, thanks to a new permanent magnet design using a drilled soft iron pole.

All the different Auger decay paths of Argon 2p holes have been characterized using a time of flight spectrometer of the magnetic bottle type. All electrons (the photoelectron and up to three Auger electrons) are detected in coincidence and resolved in energy. Double Auger decay is shown to proceed either through a direct process or by intense cascade paths, implying highly excited autoionizing Ar2+ states, which are identified as Ar2+ 3s−2 correlation satellites. Triple Auger decay is also observed and estimated to account for 0.2% only of all Auger decay.

We have studied, for the first time by electron spectroscopy, the Auger decay of the 4d→nf (n=4,5) resonances in Xe^{5+} ion. By detecting in coincidence the Auger electrons with the resulting Xe^{6+} ions, we unravel the contribution of the different final ionic states to the total cross section measured by ion spectroscopy. A strong intensity of 5s5p satellite lines has been observed, up to 4 times stronger than the 5s^{2} main lines. This unexpected behavior is confirmed by multiconfiguration Dirac-Fock calculations. This technique provides the most stringent test for theoretical models and allows us to disentangle the contribution of ions in the ground and metastable states in the target beam.

Direct measurements of the photoelectrons or Auger electrons associated with inner shell ionization of positively charged ions are extremely difficult and rarely realized. We propose an alternative method to simulate such measurements, based on core valence double photoionization of the neutral species. As an example, we obtain the spectroscopy, lifetimes, and Auger decays of the states arising from $2p$ inner shell ionisation of an ${\mathrm{Ar}}^{+}$ ion. Observations compare well with theoretical predictions obtained within multiconfigurational Dirac-Fock formalism.

Direct measurements of the photoelectrons or Auger electrons associated with inner shell ionization of positively charged ions are extremely difficult and rarely realized. We propose an alternative method to simulate such measurements, based on core valence double photoionization of the neutral species. As an example, we obtain the spectroscopy, lifetimes, and Auger decays of the states arising from 2p inner shell ionisation of an Ar(+) ion. Observations compare well with theoretical predictions obtained within multiconfigurational Dirac-Fock formalism.

We have observed single photon double K-shell photoionization in the C(2)H(2n) (n=1-3) hydrocarbon sequence and in N(2) and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K(-2) process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (K(-1)K(-1) process). In the C(2)H(2n) sequence, the spectroscopy of K(-1)K(-1) states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single K-shell ionization. The cross section variation for single photon K(-1)K(-1) double core ionization in the C(2)H(2n) sequence and in the isoelectronic C(2)H(2n), N(2) and CO molecules validates a knock-out mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.

We observe the formation in a single-photon transition of two core holes, each at a different carbon atom of the C2H2 molecule. At a photon energy of 770.5 eV, the probability of this 2-site core double ionization amounts to 1.6 ± 0.4% of the 1-site core double ionization. A simple theoretical model based on the knockout mechanism gives reasonable agreement with experiment. Spectroscopy and Auger decays of the associated double core hole states are also investigated.

Vibrational excitation of H2O and D2O by electron impact to high vibrational levels with energies up to 3 eV has been studied in the 4 eV to 10 eV incident energy range. The excitation cross sections are dominated throughout this energy range by a broad short-lived resonance that yields excitation of two vibrational progressions that are tentatively assigned to be predominantly (n,0,1) and (n,1,1). The 2B1 resonance at 6.5 eV, well known in dissociative attachment, was also observed to yield vibrational excitation. The 2A1 resonance at 8.5 eV, also identified in dissociative attachment, was not detected in the vibrational excitation spectra. A spectacular interference effect was observed between the 'broad' and 2B1 resonances extending over 2 eV in the differential cross sections of higher vibrational levels. The angular characteristics of the interference profile lead A1 symmetry to be proposed for the 'broad' resonance. Strong isotope effects were detected in all the observed phenomena.

International audience; The Auger decay of the 4d → nf (n = 4 to 6) photoexcitations in Xe5+ ion has been measured using electron spectrometry. MCDF calculations allow to interpret the recorded electron spectra.

Direct measurements of the photoelectrons or Auger electrons associated with inner shell ionization of positively charged ions are extremely difficult and rarely realized. We use here an alternative method to simulate such measurements, based on core-valence double photoionization of the neutral species. As an example, we obtain the spectroscopy, lifetimes and Auger decays of the states arising from 2p inner shell ionization of an Ar+ ion. Observations compare well with theoretical predictions obtained with multiconfigurational Dirac-Fock formalism.

We have investigated both experimentally and theoretically the post collision interaction effect on Argon 2s photoelectrons in the case of cascade double Auger decay. New features of this effect are revealed.

Quantitative results have been obtained for vibrational excitation of both H2 and D2 by electron impact at 10 eV. A strong isotope effect is observed for the lowest levels where the X 2 Sigma u+ resonance produces the main contribution. The B 2 Sigma g+ resonance is only observed weakly in the high vibrational level cross sections. Vibrational excitation was also observed at 5 eV where only the X 2 Sigma u+ resonance is present. The near-threshold cross section of the b 3 Sigma u+ state was determined with the aim of observing the B 2 Sigma g+ resonance in this channel. No such contribution was detected, the cross section appeared to be dominated by direct scattering.

The angular behaviour of the differential cross sections for vibrational excitation of N2O by electron impact has been measured in the 1.4-3.1 eV energy range. These observations have been interpreted using angular correlation theory and lead one to propose that both Sigma and Pi resonances are present, each with only one contributing partial wave. Above 2.4 eV the Pi contribution would be twice that of Sigma and below 1.8 eV only the Sigma state would be present. These conclusions have been shown to be consistent with the angular distributions for O- formation measured previously where a reinterpretation of these results would also indicate the presence of both resonances. Finally, an angular study of vibrational excitation through the 8 eV resonance indicates Sigma symmetry with a single p sigma wave.

Resonant electron scattering from SO2 has been observed in the 2.5 to 4.5 eV energy region. Vibrational excitation of the nu 1 mode with up to 23 quanta has been detected with some additional bending quanta. The angular behaviour of the absolute differential cross sections allied to configuration arguments indicate a shape resonance of B2 symmetry. A reasonable theoretical description was obtained with the boomerang model but a weakness in the usual model for Gamma was brought to light.

Electron scattering from acetylene has been studied at low energies by means of an electron impact spectrometer. The 2.5 eV Pi g resonance was seen to lead to appreciable excitation of the nu 4 bending mode and the observed angular dependences of the scattered electrons could only be reconciled with angular correlation theory by assuming a bent geometry for this resonance and consequently a lowering of the molecular symmetry. A 2 Sigma +g resonance was located at 6 eV and is the analogue of that observed in isoelectronic N2 at 8 eV. Further information has been obtained on the Feshbach resonance series and assignments have been proposed based on the grandparent model.