V Schmidt

Differential cross sections for photo-double-ionization of the helium atom

A rather complete understanding is emerging of the process of full fragmentation of the helium atom following absorption of a single photon. In this review the major experimental and theoretical advances that have led to our understanding of this simplest photo-double-ionization process, particularly with respect to multiply differential cross sections, are described.

Absolute ionisation cross sections for electron impact in rare gases

Absolute ionisation cross sections sigma n+ (n=1, 2, 3) for electron impact (with energies between 0.5 and 5.0 keV) with rare gases have been determined by a direct method. The values are generally in close agreement with the results of Schram et al. (see Physica, vol.32, p.185, 1966). A comparison with other experimental data and to some theoretical calculations is given.

Inner-shell photoionisation in molecules: the carbon monoxide case

The inner-valence-shell photoionisation of CO has been studied by electron spectrometry using monochromatised synchrotron radiation in the region of 34 to 100 eV. The analysis of the experimental data and the quantitative comparison with theoretical calculations illustrate the important role electron correlation and shape resonances play in the explanation of the main features of these photoelectron spectra.

Vibronic coupling and other many‐body effects in the 4σ−1g photoionization channel of CO2

Vibrational branching ratios and photoelectron angular distributions were measured for 4σ−1g photoionization of CO2 in the energy range 20–28 eV. Of particular interest are three vibrational components of the resulting CO+2 C 2Σ+g state—the allowed (000) and (100) bands and the forbidden (101) band. The wavelength dependence of the beta parameter for the forbidden band deviated significantly from that of the two allowed bands, showing instead a strong resemblance to that of the B 2Σ+u state. This behavior suggests that vibronic coupling to the B 2Σ+u state is responsible for the appearance of the forbidden (101) band in the C 2Σ+g state photoelectron spectrum. We also observe evidence for other many‐body effects—shape‐resonance‐induced continuum–continuum coupling and doubly excited autoionizing resonances—in the present data.

Direct measurement for the decay probabilities of 4dj hole states in xenon by means of photoelectron-ion coincidences

The decay probabilities of the 4dj hole states in xenon into the differently charged ion states, i.e. fluorescence decay, normal Auger together with discrete double Auger decay and continuous double Auger decay, are measured directly by means of coincidences between 4dj photoelectrons and xenon ions. Special emphasis is given to the strength of continuous double Auger transitions which is a direct manifestation of strong electron correlations during the non-radiative decay. In order to obtain reliable values, the problem for the correct extraction of true coincidences from the observed ones is also discussed in detail.

Polarisation determination of monochromatized synchrotron radiation

Abstract The angular distribution of photoelectrons following 1s-ionisation in helium with asymmetry parameter β = 2 is used to determine the polarisation quantities of the monochromatized synchrotron radiation in the interaction region with the target. Emphasis is put on the capability of this method to determine the β-parameters of other processes or targets. Especially, the results are checked against the β-values for 2p-ionisation in neon. Very good agreement with other experimental data of high quality is found.

Resonance and threshold effects in atomic and molecular photoionization

Photoionization processes depend critically on the behavior of the bound and continuum state wave functions involved in the ionization process. Resonance and threshold effects, as they show up in the photoemission cross section, are discussed within this context.

Complete description of 3p photoionization in calcium

Within the dipole approximation and the LS-coupling limit 3p photoionization in atomic calcium is described completely by two matrix elements and one relative phase. These three parameters are extracted from experimental observables and compared with theoretical calculations (RRPA transformed to the non-relativistic limit) for photon energies around the Cooper minimum in the 3pd channel. Taking into account the intensity-borrowing model, excellent agreement between theoretical and experimental data is found.

Correlation satellites in the outer-shell photoelectron spectrum of argon

The authors present satellite photoelectron spectra from the outer shell of argon whose binding energies range from 32 to 43 eV, using synchrotron radiation in the 40-80 eV photon energy region. It has been possible to obtain satellite spectra much better resolved than those previously obtained by Spears et al. (1974) as well as to observe new satellite lines appearing only at low photon energy. An assignment is proposed for all the satellites observed by the authors. These experimental results show that the 3s3p6 2S to 3s23p4ns, nd 2S transfer has been fairly well accounted for by the theoreticians, but they also show clearly that the satellite spectra following photoionisation in the outer shell of argon arise from both the 3s and 3p subshells and that the final-ionic-state configuration-interaction mechanism describes only part of the spectrum.

PCI and interference effects in the energy and angular correlation between the photoelectron and the Auger electron for equal electron energies

Photoionization in the inner shell of an atom followed by Auger decay is considered for the case of equal energies of the emitted electrons. Due to the indistinguishability of both electrons it is imperative to describe this process as resonance embedded in the double ionization continuum, i.e. within the one-step formulation. As a consequence, two amplitudes appear where either one of the two electrons with momenta and is connected to the photoprocess, and correspondingly the other to the Auger decay. We have accounted for the modification of these amplitudes by post-collision interaction (PCI). To elucidate our theoretical treatment we have selected a simple example and demonstrate how both exchange and PCI strongly modify by interference the energy- and angle-dependent correlation patterns of coincident two-electron emission.