Investigations on the fragmentation and ionization of endohedral fullerenes using synchrotron radiation

Cross-section measurements employing the photon-ion merged-beam technique for photoionization and photofragmentation of ions of endohedral fullerenes Xe@C$_{60}$ and Lu$_3$N@C$_{80}$ exposed to synchrotron-generated extreme ultraviolet light and soft x-rays are presented. A part of the required Xe@C$_{60}$ material was synthesized with the production apparatus available at the Institute for Atomic and Molecular Physics (IAMP) in Gießen. A list of modifications to apparatus and production methods facilitated an increase in the endohedral yield by a factor of 30. Xe@C$_{60}$ measurements were carried out at the synchrotron facility Advanced Light Source (ALS) at the Lawrence Berkeley National Laboratory (LBNL) in Berkeley. The current study extends previous efforts on single and double ionization of Xe@C$_{60}+$ as well as fragmentation channels towards triple ionization with fragmentation of Xe@C$_{60}+$ and towards double ionization with fragmentation of negative Xe@C$_{60}-$ ions in the photon energy range 60–150 eV. The relative cross-section data were normalized to absolute measurements either directly or the relative cross sections were scaled to match absolute cross-section data of pristine fullerenes in the respective channels at energies where the encapsulated xenon does not contribute. The excess cross section due to the encapsulated atom is determined by comparison of pristine and endohedral fullerene. The experimental results are compared to previously published measurements for Xe@C$_{60}+$ double ionization.Relative cross-section measurements for Lu$_3$N@C$_{80}$ were carried out at the synchrotron facility PETRAIII of the Deutsches Elektronen-Synchrotron (DESY) in Hamburg. Prominent structures related to the carbon K-shell ionization threshold were observed in the energy range 280–330 eV. These resonance structures have been analyzed in seven product channels and are compared with previously known absorption spectra of several fullerene species. Unlike for Xe@C$_{60}$, no signatures of the encapsulated atoms have been found particularly searching for the N-1s and Lu-3d thresholds in the energy ranges 390–435 eV and 1500–1700 eV. The carbon K-shell threshold seen in double ionization of Lu$_3$N@C$_{80}^{2+}$ is shifted by $\Delta$ E = (2.90$\pm$0.24) eV with respect to the carbon K-shell threshold in double ionization of Lu$_3$N@C$_{80}^{ +}$. The shift is explained by the difference in the Coulomb potentials of singly and doubly charged and Lu$_{3}$N@C$_{80}$. An outer endohedral fullerene radius R=(5.0$\pm$0.4) x 10$^{-10}$ m is inferred. Comparison with Sc$_{3}$N@C$_{80}$ indicates that Lu$_3$N has an identical influence on the C$_{80}$ behavior at the carbon K-shell as Sc$_3$N

Investigations on the fragmentation and ionization of endohedral fullerenes using synchrotron radiation

Cross-section measurements employing the photon-ion merged-beam technique for photoionization and photofragmentation of ions of endohedral fullerenes Xe@C$_{60}$ and Lu$_3$N@C$_{80}$ exposed to synchrotron-generated extreme ultraviolet light and soft x-rays are presented. A part of the required Xe@C$_{60}$ material was synthesized with the production apparatus available at the Institute for Atomic and Molecular Physics (IAMP) in Gießen. A list of modifications to apparatus and production methods facilitated an increase in the endohedral yield by a factor of 30. Xe@C$_{60}$ measurements were carried out at the synchrotron facility Advanced Light Source (ALS) at the Lawrence Berkeley National Laboratory (LBNL) in Berkeley. The current study extends previous efforts on single and double ionization of Xe@C$_{60}+$ as well as fragmentation channels towards triple ionization with fragmentation of Xe@C$_{60}+$ and towards double ionization with fragmentation of negative Xe@C$_{60}-$ ions in the photon energy range 60–150 eV. The relative cross-section data were normalized to absolute measurements either directly or the relative cross sections were scaled to match absolute cross-section data of pristine fullerenes in the respective channels at energies where the encapsulated xenon does not contribute. The excess cross section due to the encapsulated atom is determined by comparison of pristine and endohedral fullerene. The experimental results are compared to previously published measurements for Xe@C$_{60}+$ double ionization.Relative cross-section measurements for Lu$_3$N@C$_{80}$ were carried out at the synchrotron facility PETRAIII of the Deutsches Elektronen-Synchrotron (DESY) in Hamburg. Prominent structures related to the carbon K-shell ionization threshold were observed in the energy range 280–330 eV. These resonance structures have been analyzed in seven product channels and are compared with previously known absorption spectra of several fullerene species. Unlike for Xe@C$_{60}$, no signatures of the encapsulated atoms have been found particularly searching for the N-1s and Lu-3d thresholds in the energy ranges 390–435 eV and 1500–1700 eV. The carbon K-shell threshold seen in double ionization of Lu$_3$N@C$_{80}^{2+}$ is shifted by $\Delta$ E = (2.90$\pm$0.24) eV with respect to the carbon K-shell threshold in double ionization of Lu$_3$N@C$_{80}^{ +}$. The shift is explained by the difference in the Coulomb potentials of singly and doubly charged and Lu$_{3}$N@C$_{80}$. An outer endohedral fullerene radius R=(5.0$\pm$0.4) x 10$^{-10}$ m is inferred. Comparison with Sc$_{3}$N@C$_{80}$ indicates that Lu$_3$N has an identical influence on the C$_{80}$ behavior at the carbon K-shell as Sc$_3$N

Photoionization and photofragmentation of multiply charged Lu3N@C80\mathrm{Lu_3N@C_{80}} ions

Relative cross sections for photoionization of endohedral fullerene ions Lu$_3$N@C$_{80}$$^{q+}$ (q=1,2,3) have been measured employing the photon-ion merged-beam technique. The investigations include various ionization channels Lu$_3$N@C$_{80}$$^{+q→+p}$ (q=1,2,3 and p=2,3,4,5,6), in some cases accompanied by fragmentation of the carbon cage. Prominent structures related to the carbon K-shell ionization threshold were observed in the energy range 280–330 eV. These resonance structures have been analyzed in seven product channels and are compared with previously known absorption spectra of several fullerene species. Within the statistical significance of the data, we do not observe any signatures of the N 1s and Lu 3d thresholds in the energy ranges 390–435 eV and 1500–1700 eV, respectively. By comparing the energies for double ionization ofLu$_3$N@C$_{80}$$^{+}$ and Lu$_3$N@C$_{80}$$^{2+}$ at the carbon 1s K-shell threshold, we derive a value of 5.0±0.4Å for the radius of the carbon cage

Photoionization and Photofragmentation of Multiply Charged Lu3NLu_3N @C80q+C^{q+}_{80} Ions

Photoionization and photofragmentation of Lu3N@C80 endohedral fullerene ions (in charged states q = 1+; 2+; 3+) has been studied using the new Photon-Ion spectrometer at PETRAIII (PIPE). Solid endohedral fullerene material was evaporated inside an ECR ion source. The generated ions were mass/charge selected and the ion beam was merged with the photon beam from PETRAIII beamline P04. Product-ion yields normalized to ion current and photon flux, i.e., relative cross sections, were measured as a function of photon energy. The experimental photon-energy range was 270-1700 eV. This range comprises the energies for 1s ionization of carbon and nitrogen as well as for 3d-ionization of lutetium. The measured spectra exhibit clear signatures of carbon K-shell excitation, but no signs of excitation or ionization of encapsulated N or Lu producing vacancies in the 1s and 3d shells, respectively, have been observed. This is in contrast to recent findings for photofragmentation of Xe@C60+ [1] at energies of 60-150 eV. We speculate that the carbon cage and the encaged Lu3N molecule completely disintegrate into relatively small fragments after absorption of one energetic photon. [1] R. A. Phaneuf et al., Phys. Rev. A 88, 053402 (2013)

Photoabsorption of the molecular IH cation at the iodine 3d absorption edge

Yields of atomic iodine I$^{q+} (q≥2)$ fragments resulting from photoexcitation and photoionization of the target ions $IH^+$ and $I^+$ have been measured in the photon-energy range 610–680 eV, which comprises the thresholds for iodine $3d$ ionization. The measured ion-yield spectra show two strong and broad resonance features due to the excitation of the $3d_{3/2,5/2}$ electrons into ɛf states rather similar for both parent ions. In the $3d$ pre-edge range, excitations into $(npπ)$-like orbitals and into an additional $σ^*$ orbital are found for $IH^+$, which have been identified by comparison of the atomic $I^+$ and molecular $IH^+$ data and with the help of (time-dependent) density functional theory (DFT) and atomic Hartree-Fock calculations. The $(5pπ)$ orbital is almost atomlike, whereas all other resonances of the $IH^+$ primary ion show a more pronounced molecular character, which is deduced from the chemical shifts of the resonances and the theoretical analysis

Breakthrough in near-K-edge photoionization of singly and multiply charged ions

In the energy region of the astrophysically important K-edge of Cq+ ions with q=1,2,3,4 and of Neq+ ions with q=1,2,3 absolute cross sections for single and multiple photoionization by single photons from the PETRA III light source were measured. Different from all previousphotoionization and photoexcitation experiments with ions other than He+ and Li+, the whole energy range around the K-edge could be covered from the lowest-energy resonances involving K-shell excitation to beyond the K-shell ionization threshold including double excitationsof both a K- and an L-shell electron. Moreover, not only single ionization but also multiple ionization could be addressed in photon-ion K-shell experiments for the first time.The photon beam energy resolution reached down to better than 9 meV at 336 eV, that is, aresolving power of more than 37000 could be accomplished. Emission of up to 3 electronsfrom ions with a K-vacancy could be observed. First unambiguous evidence was obtained fortriple-Auger decay processes. This demonstration was facilitated by the unique capability ofphoton-ion experiments to study iso-electronic sequences, i.e., atomic systems with equal numbersof electrons but different nuclear charge. Thereby, a suitable ionic configuration can beselected and with the low bandwidth of the photon beam also very well specified levels can beexcited leaving only one interpretation of an observed triple ionization to be due to triple-Augerdecay.In the case of C4+ parent ions spectroscopic measurements of intermediate hollow atoms (hollowions) with 2 vacancies in the K-shell were performed. This was made possible by producinga beam of C4+ containing a significant fraction of ions in the metastable 1s2s 3S1 level. Singleexcitation of such an ion, which already carries an excitation energy of almost 300 eV into theinteraction with a photon, results in a double–K-vacancy state.The experiments were carried out at the newly constructed endstation PIPE, the Photon-IonSpectrometer at PETRA III, which is an experimental facility for studying interactions of singlephotons with charged particles [1] (atomic ions, molecular ions, electrically charged clustersand nanoparticles). It has been set up at the Variable Polarization XUV beamline P04 atPETRA III

Near-K -edge single, double, and triple photoionization of C+C^{+} ions

Single, double, and triple ionization of the $C^{+}$ ion by a single photon have been investigated in the energy range 286 to 326 eV around the K-shell single-ionization threshold at an unprecedented level of detail. At energy resolutions as low as 12 meV, corresponding to a resolving power of 24 000, natural linewidths of the most prominent resonances could be determined. From the measurement of absolute cross sections, oscillator strengths, Einstein coefficients, multielectron Auger decay rates, and other transition parameters of the mainK-shell excitation and decay processes are derived. The cross sections are compared to results of previous theoretical calculations. Mixed levels of agreement are found despite the relatively simple atomic structure of the $C^{+}$ ion with only five electrons. This paper is a followup to a previous Letter [A. Müller et al., Phys. Rev. Lett. 114, 013002 (2015)]

Präzisionsspektroskopie an der K-Kante astrophysikalisch relevanter Ionen

Absolute Wirkungsquerschnitte für die Einfach- und Mehrfach-Ionisation von Cq+ - Ionen mit q=1,2,3,4 und Neq+-Ionen mit q=1,2,3durch einzelne Synchrotronstrahlungs-Photonen wurden an dem neu an PETRA III aufgebauten Photon - Ion Experiment PIPE (Photon-Ion Spectrometer at PETRA III) gemessen. Energieauflösungen der Photonenstrahlen bis herab zu 5 - 10 meV bei 330 eV wurden realisiert. Die abgedeckten Energiebereiche umfassen die niederenergetischsten mit Anregung eines K-Elektrons verknüpften Resonanzen bis hin zu autoionisierenden Zuständen mit Doppelanregung (K- und L-Schale) bei Energien jenseits der eigentlichen Ionisationskante der jeweiligen K-Schale. Emission von bis zu 3 Elektronen aus Ionen mit einem K-Loch wurde beobachtet. Im Fall von C4+ - Ionen wurden intermediäre Hohlatome (hohle Ionen) mit zwei Löchern in der K-Schale spektroskopiert

Анонс как речевой жанр (на материале интернет-дискурса)

Single, double, and triple photoionization of Ne$^{+}$ ions by single photons have been investigated at the synchrotron radiation source PETRA III in Hamburg, Germany. Absolute cross-sections were measured by employing the photon–ion merged-beams technique. Photon energies were between about 840 and 930 eV, covering the range from the lowest-energy resonances associated with the excitation of one single K-shell electron up to double excitations involving one K- and one L-shell electron, well beyond the K-shell ionization threshold. Also, photoionization of neutral Ne was investigated just below the K edge. The chosen photon energy bandwidths were between 32 and 500 meV, facilitating the determination of natural line widths. The uncertainty of the energy scale is estimated to be 0.2 eV. For comparison with existing theoretical calculations, astrophysically relevant photoabsorption cross-sections were inferred by summing the measured partial ionization channels. Discussion of the observed resonances in the different final ionization channels reveals the presence of complex Auger-decay mechanisms. The ejection of three electrons from the lowest K-shell-excited Ne$^{+}$$(1s 2s^{2}$ $2p^{6}$ $^{2}$$S_{1/2})$ level, for example, requires cooperative interaction of at least four electrons