The photoionization and subsequent Auger decay of the 2s subshell in vapor phase potassium are investigated using multielectron coincidence spectroscopy with synchrotron radiation. This method, capable of detecting multiple particles simultaneously, enables a comprehensive description of all cascade decay paths of the K 2s vacancy. It establishes, at each step of the 2s cascade decay, whether the outer 4s electron is a spectator or participates in the decay. The study determines the populations of the cascade final state and the different ionization rates. Experimental findings are compared with theoretical predictions derived from the multiconfiguration Dirac-Fock approach and previous observations of cascade processes in argon, emphasizing differences attributed to the presence of an additional 4s electron. The research contributes to our understanding of the electronic structure of potassium and quantum mechanical transition processes.

We report measurements of the absolute photoionization cross sections of magnesiumlike S4+ over the 158-280 eV photon energy range. The experiments were performed with the multianalysis ion apparatus at the SOLEIL synchrotron radiation facility. Single-and double-ionization ion yields produced by the photoionization of the 2p subshell of the S4+ both from the 2p63s2 1S0 ground state and the 2p53s3p 3P0,1,2 metastable levels were observed, as well as 2s excitations. Theoretical calculations of the photoionization cross sections were carried out using multiconfiguration Dirac-Fock and R-matrix computer codes and the results are compared with the experimental data. While in general reasonably good agreement was found, notable differences in the strengths and positions of predicted resonances were observed and significant systematic energy shifts of the theoretical predictions were required.

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 Xen+ ions in coincidence with n electrons. This new coincidence detection allows more efficient extraction of minor channels that are otherwise masked by random coincidences. The proof of principle is provided for xenon triple ionization.

Synopsis Single and double photoionization cross-sections in the photon region straddling the nitrogen K-edge and up to photon energies of ∼450 eV, for the atomic N+ and molecular NH+ and NH 2 + species were measured at the SOLEIL radiation facility in Orsay, France. The measurements are compared with theoretical estimates.

Synopsis We present here the different Auger decay paths following 3d inner-shell ionization of Rubidium atom and we observe the peculiar behaviour and correlation effects due to the outer, unpaired 5s electron. This electron can be submitted to shake-up during 3d ionization. Also shake-up and shake-down of the outer electron are observed in the Auger decay. Cascade double Auger decay is the dominant process leading to Rb3+ ion.

Single photon simultaneous core ionization/core excitation (K-2V) of the Benzene molecule has been observed experimentally, using synchrotron radiation, by electron coincidence spectroscopy with a magnetic bottle time-of-flight electron spectrometer and reveals a rich spectrum. DFT and Post-Hartree-Fock calculations provide detailed assignments of K-2V states. The specific Auger decay of these states has also been determined experimentally with a new technique to improve the energy resolution.

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.

For an atomic state with two electrons missing from different core orbitals one may assume that the deeper hole decays first. However, it is quite probable that the double core-hole state will decay by emission of a slow Auger electron where the deeper core hole remains a spectator, especially if the outer core hole can be filled by Coster-Kronig transition, while the deeper cannot. We study here the competition of both Auger decay channels in a model system, the 1s2s2p(6) (3s/3p) states of Ne+ ions. As the phenomenon can take place in any decay chain involving multiple core-excited states it can be critical to understand the ion yields, the electron and x-ray emission spectra, and the molecular fragmentation.

We report on complementary theoretical and laboratory investigations of the 2p ion yield cross sections for the molecular-ion series SiH n + (n = 1, 2, 3), in the 95-108 eV photon energy range, below the L-shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatised synchrotron radiation in a merged-beam configuration. The experimental spectra are compared with total photoabsorption cross-sectional profiles calculated using an ab initio configuration interaction method inclusive of spin-orbit coupling and the vibrational dynamics. The experimental results show vibrationally resolved resonances for SiH 2 + in the 98-102 eV range. The calculations indicate twenty four core-excited states below the energy of 102 eV, of which only four contribute significantly to the observed spectrum. These states correspond to the excitation of an atomic-like 2p electron to the SiH 2 + (5a 1 ) valence orbital.

Synopsis Photoionization measurements of NO+ at Nitrogen K-shell, performed at the SOLEIL Light Source will be presented. The main observed structure corresponds to the 1s to π* resonant transition.

We report on complementary laboratory and theoretical investigations of the $2p$ photoexcitation cross sections for the molecular-ion series $\mathrm{Si}{{\mathrm{H}}_{n}}^{+}$ ($n=1,2,3$) near the $L$-shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatized synchrotron radiation in a merged-beam configuration. For all three molecular ions, the $\mathrm{S}{\mathrm{i}}^{2+}$ decay channel appeared dominant, suggesting similar electronic and nuclear relaxation patterns involving resonant Auger and dissociation processes, respectively. The total yields of the $\mathrm{S}{\mathrm{i}}^{2+}$ products were recorded and put on absolute cross-section scales by comparison with the spectrum of the $\mathrm{S}{\mathrm{i}}^{+}$ parent atomic ion. Interpretation of the experimental spectra ensued from a comparison with total photoabsorption cross-sectional profiles calculated using ab initio configuration interaction theoretical methods inclusive of vibrational dynamics and contributions from inner-shell excitations in both ground and valence-excited electronic states. The spectra, while broadly similar for all three molecular ions, moved towards lower energies as the number of screening hydrogen atoms increased from one to three. They featured a wide and shallow region below $\ensuremath{\sim}107\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ due to $2p\ensuremath{\rightarrow}{\ensuremath{\sigma}}^{*}$ transitions to dissociative states, and intense and broadened peaks in the $\ensuremath{\sim}107--113\ensuremath{-}\mathrm{eV}$ region merging into sharp Rydberg series due to $2p\ensuremath{\rightarrow}n\ensuremath{\delta},n\ensuremath{\pi}$ transitions converging on the ${L}_{\mathrm{II},\mathrm{III}}$ limits above $\ensuremath{\sim}113\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. This overall spectral shape is broadly replicated by theory in each case, but the level of agreement does not extend to individual resonance structures. In addition to the fundamental interest, the work should also prove useful for the understanding and modeling of astronomical and laboratory plasma sources where silicon hydride molecular species play significant roles.

Resonant single photoionization cross sections of Fen+ (n = 6 to 10) ions have been measured in absolute values using a merged-beams setup at the SOLEIL synchrotron radiation facility. Photon energies were between about 710 and 780 eV, covering the range of the 2p-3d. transitions. The experimental cross sections are compared to calculations we performed using a multi-configuration Dirac-Fock code and the OPAS code dedicated to radiative opacity calculations. Comparisons are also done with the Chandra X-ray observatory NGC 3783 spectra and with the results of previously published calculations.

We report on complementary laboratory and theoretical investigations of the 2p photoexcitation cross sections for the molecular-ion series SiHn+ (n = 1,2,3) near the L-shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatized synchrotron radiation in a merged-beam configuration. For all three molecular ions, the Si2+ decay channel appeared dominant, suggesting similar electronic and nuclear relaxation patterns involving resonant Auger and dissociation processes, respectively. The total yields of the Si2+ products were recorded and put on absolute cross-section scales by comparison with the spectrum of the Si+ parent atomic ion. Interpretation of the experimental spectra ensued from a comparison with total photoabsorption cross-sectional profiles calculated using ab initio configuration interaction theoretical methods inclusive of vibrational dynamics and contributions from inner-shell excitations in both ground and valence-excited electronic states. The spectra, while broadly similar for all three molecular ions, moved towards lower energies as the number of screening hydrogen atoms increased from one to three. They featured a wide and shallow region below similar to 107 eV due to 2p -> sigma* transitions to dissociative states, and intense and broadened peaks in the similar to 107-113-eV region merging into sharp Rydberg series due to 2p -> n delta, n pi transitions converging on the L-II,L-III limits above similar to 113 eV. This overall spectral shape is broadly replicated by theory in each case, but the level of agreement does not extend to individual resonance structures. In addition to the fundamental interest, the work should also prove useful for the understanding and modeling of astronomical and laboratory plasma sources where silicon hydride molecular species play significant roles.

Resonant photoionization cross sections of Mnn+ (n = 5 to 8) ions are measured in absolute values in the photon energy range of the 2p -> 3d transitions (645-690 eV) using a merged-beams setup at the SOLEIL synchrotron radiation facility. The experimental cross sections are compared to calculations we performed using a multiconfiguration Dirac-Fock code and the OPAS code dedicated to radiative opacity calculations of hot and dense plasmas. Both calculations reproduce the measurements well.

1 Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire de Chimie Physique-Matière et Rayonnement (LCP-MR), 4 place Jussieu 75005 Paris, France 2 Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin, F-91192 Gif-sur-Yvette cedex, France 3 ISMO, CNRS UMR 8214, Université Paris-Sud, Bâtiment 350, F-91405 Orsay cedex, France 4 Department of Physics, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland 5 Jozef Stefan Institute, Jamova cesta 39, SI-1001 Ljubljana, Slovenia 6 Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 930-0194, Japan

A magnetic bottle time-of-flight spectrometer has been used to perform spectroscopy of Kn+ and Rbn+ states with ionization degrees n of 2, 3 and 4. Energy levels are directly measured by detecting in coincidence the n electrons that are emitted as a result of single photon absorption. Experimental results are compared with the energies from the NIST atomic database and ab initio multiconfiguration Dirac–Fock calculations. Previously unidentified 3p4(3P)3d1 4D energy levels of K2+ are assigned.

* Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire de Chimie Physique-Matière et Rayonnement (LCP-MR), 4 place Jussieu 75005 Paris, France † ISMO, CNRS UMR 8214, Université Paris-Sud, Bâtiment 350, F-91405 Orsay cedex, France ‡ Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin, F-91192 Gif-sur-Yvette cedex, France § Department of Physics, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland

We have studied Xe + 4d inner shell photoionization in a direct experiment on Xe + ions, merging an ion and a photon beam and detecting the ejected electrons with a cylindrical mirror analyzer. The measured 4d photoelectron spectrum is compared to the 4d core valence double ionization spectrum of the neutral Xe atom, obtained with a magnetic bottle spectrometer. This multi-coincidence experiment gives access to the spectroscopy of the individual Xe 2+ 4d -1 5p -1 states and to their respective Auger decays, which are found to present a strong selectivity. The experimental results are interpreted with the help of ab-initio calculations