Resonant two-color detachment of H\u3csup\u3e-\u3c/sup\u3e with excitation of H(\u3ci\u3en\u3c/i\u3e=2)

The cross sections for resonant two-color, two-photon detachment of H- with excitation of the degenerate H(2s) and H(2p) levels are calculated within a semiempirical adiabatic hyperspherical representation. The first photon, with energy ω1=0.4017 a.u., is resonant with the well-known Feshback 1P0 resonance below the H(n=2) threshold. The second photon, with energy ω2≥0.126 05 a.u., scans the energy region above the H(n=2) threshold over which long-range dipole-field-induced cross-section oscillations are predicted to occur. Such Gailitis-Damburg oscillations have not yet been observed experimentally. Results for various pairs of light polarization for the two photons are presented. Our resonant two-color, two-photon detachment cross sections are 8–9 orders of magnitude greater than the corresponding nonresonant, single-color, two-photon detachment cross sections obtained by Liu, Du, and Starace [Phys. Rev. A 43, 5891 (1991)]. Unmistakable evidence of long-range dipole-field effects is presented over the 5-meV energy range above the H(n=2) threshold. Furthermore, the differential cross sections for right- and left-circularly polarized, copropagating photons and especially the circular dichroism differential cross sections are shown to have nearly a full cycle of a greatly enhanced dipole-field-induced oscillation extending over the region from threshold to ≊34 meV above

Interchannel coupling effects in the spin polarization of energetic photoelectrons

Effects of the interchannel coupling on the spin polarization of energetic photoelectrons emitted from atomic Ne valence subshells are examined. Like previously obtained results for cross sections and angular distributions, the photoelectron spin polarization parameters too are found considerably influenced by the coupling. The result completes a series of studies to finally conclude that the independent particle description is inadequate for the {\em entire} range of photoionization dynamics over the {\em full} spectral energy domainComment: 7 pages, 5 figures, accepted in Phys. Rev.

Correlation structure in nondipole photoionization

The nondipole parameters that characterize the angular disribution of the photoelectrons from the 3d subshell of Cs are found to be altered qualitatively by the inclusion of correlation in the form of interchannel coupling between the $3d_{3/2}$ and $3d_{5/2}$ photoionization channels. A prominent characteristic maximum is predicted only in the parameters for $3d_{5/2}$ photoionization, while the effect for $3d_{3/2}$ is rather weak. The results are obtained within the framework of the Generalized Random Phase Approximation with Exchange (GRPAE), which in addition to the RPAE effects takes into account the rearrangement of all atomic electrons due to the creation of a 3d vacancy

Magnetic-field-averaged photoemission experiments with variable chirality

We report on a photoemission dichroism effect of magnetic origin which is measured between magnetic field averaged Fe 3p spectra measured with different chirality. By field average we mean the average of two results obtained with opposite directions of magnetization. Field averaging eliminates the linear magnetic dichroism in the angular distribution of photoelectrons, i.e., eliminates the effect of the polarization of the magnetic atoms on the photoemission angular intensity, but the alignment of magnetic moments along the magnetization axis is reflected in a sizeable angular photoemission line shape effect. By changing the chirality of the experiment, i.e., the angle between the magnetization axis and the reaction plane, different intensities are measured from the fine structure of the photoemission peak and a dichroism arises which can be qualitatively understood from atomic photoionization theory. The effect can be exploited to study the magnetic order at antiferromagnetic surfaces as well as to study in plane anisotropy effects on the distribution of magnetic domains in ferromagnets

Spin polarization in photoionization

Heinzmann U, Cherepkov NA. Spin polarization in photoionization. In: Becker U, Shirley DA, eds. VUV and Soft X-Ray Photoionization Studies, Ser. "Physics of Atoms and Molecules". Plenum; 1996: 521

Analysis of autoionization resonances in the Hg 6s2-photoionization by measurements of photoelectron polarization

Schäfers F, Schönhense G, Heinzmann U. Analysis of autoionization resonances in the Hg 6s2-photoionization by measurements of photoelectron polarization. Zeitschrift für Physik A: Hadrons and Nuclei. 1982;304(1):41-48.Measurements of the spin polarization of photoelectrons in the autoionization region of the Hg 6s2-subshell using circularly polarized synchrotron radiation and using unpolarized light from rare gas discharge lamps are reported. The results obtained show a pronounced structure across the resonances. Together with data of the cross section and its angular distribution these data from a complete parameter set for the determination of the transition matrix elements and the phase difference of the continuum wavefunctions. Evidences for strong configuration interaction and channel mixing between the open and closed channels were found. The matrix elements and their ratio vary strongly across the resonances and the relative phase shows some changes of sign. A change of the relative phase by Pi across an autoionization resonance, predicted by Fano, has been verified experimentally for the triplet resonance. We would like to express our gratitude to Professors W. Paul, G. Nöldeke and J. Kessler for their continued interest and encouragement. We thank Dr. D. Husmann, Dr. J. Hormes and B. Osterheld for their assistance in performing the experiment in Bonn. We are grateful to Dr. N.A. Cherepkov for helpful discussions and acknowledge support by the DFG and BMFT

3p fine structure of ferromagnetic Fe and Co from photoemission with linearly polarized light

Linear 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

Fe 2p photoemission magnetic dichroism with linearly polarized synchrotron radiation and with unpolarized Al K alpha radiation

We report on the measurements and analysis of Fe 2p magnetic dichroism in the angular distribution of the photoelectrons from remanently magnetized Fe(100)surfaces with unpolarized, monochromatized Al K alpha X-rays of 1486 eV energy (MDAD) and with linearly polarized synchrotron radiation of energy 800 eV (LMDAD). The two experiments verify the atomic photoionization model of (L)MDAD including the dichroism effect between field-averaged experiments of different chirality

Angle- and spin-resolved photoelectron spectroscopy of the Hg 5d10 subshell

Schönhense 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