19 research outputs found
Angle- and spin-resolved photoelectron spectroscopy of the Hg 5d10 subshell
No full textSchönhense G, Schäfers F, Heinzmann U, Kessler J. Angle- and spin-resolved photoelectron spectroscopy of the Hg 5d10 subshell. Zeitschrift für Physik A: Hadrons and Nuclei. 1982;304(1):31-40.Parameters describing electron spin polarization in Hg 5d10 subshell photoionization have been measured at rare-gas resonance wavelengths between 73.59 nm and 30.38 nm. The spin parameters as well as asymmetry parameters beta of a recent measurement are discussed in comparison with both nonrelativistic and relativistic ab initio calculations of several authors. The importance of many-electron correlations and spin-orbit coupling effects is considered. We would like to express our thanks to F. Combet Farnoux, N. Cherepkov, W. Johnson and S. Manson for useful correspondence as well as for the communication of unpublished results. This work was supported by the DFG and BMFT. One of us (G.S.) wishes to thank the Studienstiftung des Deutschen Volkes for financial support
3p fine structure of ferromagnetic Fe and Co from photoemission with linearly polarized light
No full textLinear Magnetic Dichroism in the Angular Distribution of the photoelectrons is observed in angular resolved photoemission experiments with linearly polarized light on 3p core levels of the ferromagnetic transition metals. The measured magnetic asymmetry is strictly related to the one observed in photoemission with circularly polarized radiation. Atomic theory shows that the effect is proportional to the state multipoles that characterize the polarization of the hole levels under the exchange interaction. By peak-fitting the experimental dichroic core level spectra and by calculating the relevant multipoles one can resolve the fine structure of the 3p core hole states of ferromagnetic Fe and Co and obtain the mjordering of the sublevels. We show that the energy order for the 3p hole-levels of Fe and Co is reversed for the J= 3 2 and J= 1 2 multiplets, and that spin-selected lineshapes can be derived from our analysis and compared with spin-resolved photoemission data
MANY-BODY EFFECTS ON DEEP LEVEL SPECTRA OF METALS
No full textMany-body effects in metals due to a change in the core electron occupation number appear in a large number of spectroscopies. The possible importance of the core hole has been realized and discussed for a very long time. Mahan's idea of excitons in metals gave the topic strong stimulus. First the interest was focused on threshold singularities in simple metals. The topic was thoroughly discussed in Mahan's 1974 review and declared solved and completed. This declaration was strongly challenged by Dow and collaborators. This has led to a deeper and more detailed understanding. In particular the importance of static core hole effects, of phonons, of electron bandstructure, of exchange coupling (the Onodera effect) and of spindependent phaseshifts has been realized. Thus the longstanding puzzle of the lithium edge now seems to have found its solution in terms of phonons and bandstructure and not in the MND-effect - the broad emission edge can be explained by incomplete phonon relaxation and the broad absorption edge by the one-electron density of states
RÉSULTATS THÉORIQUES RÉCENTS RELATIFS AUX SECTIONS EFFICACES DE PHOTOIONISATION DES ATOMES NEUTRES
No full textNous présentons les résultats essentiels obtenus lors de
l'étude théorique de la photoionisation des atomes neutres, à partir d'un
modèle mono-électronique à potentiel central (potentiel de Herman et Skillman),
dans un domaine d'énergies relativement faibles (moins de 1 keV). Nous mettons
en évidence la variation des sections efficaces relatives aux sous-couches 4 p,
5 p, 6 p, 4 d, 5 d, 4 f avec l'énergie des photons incidents et le numéro
atomique Z ; nous prévoyons une certaine périodicité dans le comportement des
différentes sous-couches, qu'on retrouve dans celui du déplacement de phase des
fonctions du continuum correspondantes et qui reflète les variations du
potentiel avec le remplissage des sous-couches au fur et à mesure que Z
croît.We report the main results obtained in the theoretical
study of photoionization for neutral atoms, in the low energies range (less
than 1 keV), using a single electron model with a central potential (Herman and
Skillman potential). We point at the combined Z and incident photon energy
dependence of the cross sections for 4 p, 5 p, 6 p, 4 d, 5 d, 4 f subshells ;
we predict some periodicity in the behaviour of the various subshells, that is
found again for the phase shift of corresponding continuum functions and
reflects the variation of potential with the filling up of subshells when Z
progressively increases
DOUBLE EXCITATION SATELLITES OF IODINE : THEORETICAL STUDY
No full textUne étude théorique des spectres de photoélectrons 5p et 5s de l'iode atomique [Z = 53] pour des energies de photons au dessous des seuils d'ionisation 4d est présentée dans le but de mettre en evidence l'origine d'un grand nombre de raies s'étalant sur un large domaine d'énergies [environ 20 eV] et de leur amplification pour l'energie excitatrice de la transition [MATH] [h[MATH] = 46.2 eV]. Elle montre que d'importants effets d'interaction de configurations font predominer les satellites de double excitation [configuration 5s25p35d] sur les raies parentes [configuration 5s5p5] et que leur amplification à l'énergie 46.2 eV provient des grandes valeurs des taux de désexcitation AUger dans les voies satellites.A theoretical study of 5p and 5s photoelectron spectra of iodine [Z = 53] for photon energies below the 4d ionisation thresholds is presented within the purpose of pointing out the origin of numerous lines spreading over a large energy range [about 20 eV] and of their enhancement when exciting the transition [MATH] [h[MATH] = 46.2 eV]. It shows that important configuration interaction effects make the double excitation satellites (configuration 5s25p35d) predominant over the parent lines [configuration 5s15p5) and that their enhancement is coming from the large Auger decay rates of this excited state into the satellite channels
DÉTERMINATION DE SECTIONS EFFICACES DE PHOTO-IONISATION DANS DIFFÉRENTS MODÈLES ATOMIQUES
No full textNous montrons dans ce travail qu'un modèle
monoélectronique à potentiel central suffit à rendre compte de l'existence pour
la section efficace de certaines sous-couches d'un maximum dit « de résonance »
au voisinage du seuil d'ionisation. L'amplitude et la position de ce maximum
varient avec Z. Nous comparons les valeurs obtenues pour σ4d du
xénon à partir de 2 potentiels centraux différents (le potentiel de Herman et
Skillman et le potentiel paramétrique de M. Klapisch). Nous montrons comment un
modèle simple à potentiel central peut servir de point de départ pour
introduire la relaxation du coeur de l'atome après ionisation, les effets
d'échange de l'électron éjecté avec le coeur, et certains effets de
corrélation, dits interactions « intrachannel ».In this work we show that a single electron model with a
central potential is sufficient to point at a resonance maximum for cross
section relating to some subshells, near the ionization threshold. The
amplitude and position of that maximum varie with Z. We compare the values
obtained for the Xe cross section σ4d with two different
central potentials (Herman and Skillman potential and M. Klapisch parametric
potential). We show how a simple model with a central potential can be used to
start calculations introducing core relaxation for the atom after ionization,
exchange of the ejected electron with the core and some correlation effects,
called « intrachannel » teractions
Energy dependence of the electron spin polarisation parameters for Hg 5d photoionisation with circularly polarised light
No full textSchäfers F, Heckenkamp C, Schönhense G, Heinzmann U. Energy dependence of the electron spin polarisation parameters for Hg 5d photoionisation with circularly polarised light. Journal of Physics B: Atomic, Molecular and Optical Physics. 1988;21(5):769-774.Circularly polarised VUV radiation from the storage ring BESSY was used to measure all three spin polarisation parameters of photoelectrons from the Hg 5d shell in the photon energy range from threshold to approximately 35 eV. The experimental results are compared with theoretical calculations in the relativistic and non-relativistic random-phase-approximation scheme (RRPA and RPAE respectively) and Dirac-Slater (DS) calculations. A discussion of the influence of relativistic and potential barrier effects on the experimental data is given
PHOTOIONISATION OF MULTIPLY-CHARGED IONS IN THE VUV AND X-RAY ENERGY RANGES
No full textCompte tenu du peu de résultats expérimentaux obtenus pour les ions multi-chargés en dehors de niveaux d'énergie, cet article sera essentiellement consacré à une revue de résultats théoriques relatifs aux sections efficaces de photoionisation des ions atomiques et à une discussion de leur validité en fonction des principales approximations physiques introduites dans les modèles atomiques. Cette étude couvre un domaine d'énergies étendu (de quelques eV à 20 ou 50 keV selon le numéro atomique) du fait que la photoionisation des couches internes et externes est considérée. Plusieurs points importants seront soulignés : a) les tendances générales de variation des différentes sections efficaces à l'intérieur de séquences isoélectroniques et isonucléaires, b) les différents modèles utilisés actuellement et leurs limitations, c) quelques problèmes cruciaux et difficultés non résolues seront mis en évidence, plus spécialement pour des configurations ioniques comportant des couches ouvertes (2p, 3d, 4d)Since experimental results other than energy levels are still scarce for multiply charged ions, this paper will be essentially devoted to a review of theoretical results relative to photoionisation cross sections for ions and to a discussion of their reliability in terms of the main physical approximations introduced in the atomic models. Photoionisation of both inner and outer shells of ions are considered here (from a few eV. up to 20 or 50 keV according to the atomic number). Within this framework, several important points will be emphasized : a) the general trends displayed by the variation of the various cross sections within isoelectronic and isonuclear sequences, b) the various theoretical models currently used and their limitations, c) some crucial problems and unresolved difficulties will be pointed out, especially for ionic configurations involving open subshells (2p, 3d, 4d)
I. ATOMIC AND MOLECULAR PHYSICS.ATOMIC EFFECTS IN SOLIDS
No full textCette revue concerne l'origine des structures présentées par le coefficient d'absorption, lors de mesures par plusieurs techniques, à partir d'échantillons solides. On met l'accent sur les modèles atomiques de photoionisation en raison de la ressemblance des spectres du solide et de la vapeur, dans ce domaine d'énergies (10 à 350 eV) ; mais même les modèles les plus sophistiqués qui introduisent des corrélations dans l'état initial comme dans l'état final ne permettent pas toujours un bon accord quantitatif avec l'expérience. La photoionisation de l'atome libre ne peut expliquer certaines structures fines près des seuils ni une modulation du spectre dues à la non-localisation du trou et au fait que le photoélectron est soumis à un champ issu de plusieurs centres.This review concerns the origin of the structures of the absorption coefficient measured for solid state samples by several techniques. Because of a close similarity between the solid and gaseous samples spectra, in this energy range (10 to 350 eV), atomic photoionization models are emphasized ; but the most elaborated models introducing correlation effects in both initial and final states are not always sufficient to give a good quantitative agreement with experiment. Some fine structures near the thresholds and a modulation of the spectra fail to be understood in terms of free atom photoionization because of the non-localization of the core hole and the multicenter nature of the field experienced by the photoelectron
