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The recent double-ionization experiments (e, 3 - 1e) on argon by electron impact are, for the first time, investigated theoretically. Simple qualitative models and more elaborate theoretical calculations are proposed and discussed in order to understand the mechanism of double ionization at high electron impact.

We use a novel multidetection coincidence spectrometer to study electron impact double ionization of atoms. New results in the e,(3-1)e mode have been obtained for the first time for helium, where it was not possible with previous systems, highlighting the high sensitivity of the new apparatus. The coincident angular distribution of the two slow ejected electrons has been measured at equal or unequal energy sharing of the available excess energy among the two electrons. The results are compared with preliminary (unpublished) calculations, and with similar double photoionization studies.

Autoimmune progesterone dermatitis (AIPD) is caused by an immune reaction to endogenous progesterone following exposure to exogenous progesterone, especially in oral contraceptives and intrauterine devices. Skin eruption develops cyclically during the luteal phase of the menstrual cycle when progesterone levels are elevated. The resultant clinical symptoms are frequently confused with other forms of dermatosis. We describe a young woman presenting AIPD.A 23-year-old woman had a history of a chronic pruritic papular-vesicular eruption on the trunk, present since the onset of puberty and unsuccessfully treated with antihistamines and topical steroids. Skin lesions normally began a few days before menstruation and resolved a few days afterwards. Intradermal testing using progesterone was positive, thereby confirming the diagnosis. The patient's skin lesions improved under oral contraceptives designed to inhibit ovulation and there was no relapse during subsequent menstrual cycles.AIPD is a rare autoimmune disorder. The diagnostic criteria of AIPD include recurrent cyclical worsening of skin lesions and symptomatic improvement after inhibition of progesterone secretion by suppression of ovulation. The pathogenesis is unclear. Positive response to various tests with progesterone suggests involvement of various mechanisms such as antibodies and/or cell-mediated immune reactions.AIPD is a rare disease that can seriously affect patients' quality of life and which may even be life-threatening in certain cases.

Recent measurements of the (e, 3-1e) fourfold differential cross sections for the double ionization of helium are here extended to more complex targets, namely neon, argon and molecular nitrogen. The previous observations of large angular shifts in the experimental fourfold differential cross section (4DCS) distributions with respect to the momentum transfer axis and the existence of structures in these distributions are found to similarly hold here. For the three investigated targets, the experimental data are compared with the kinematical analysis previously given to describe the second-order, 'two-step 2' (TS2) double ionization (DI) mechanism. Such a comparison confirms our interpretation which allows the observed shifts and structures in the intensity distributions to be mostly related to the 'two-step 2' mechanism, which is shown to predominate over the first-order 'shake-off' (SO) and 'two-step 1' (TS1) mechanisms under the present kinematics. The experimental data are also compared to the predictions of a first Born and second Born model, showing rather mixed agreement.

Granular cell tumor (GCT), also known as Abrikossoff tumor, is a rare and benign neoplasm that more commonly affects the oral cavity in adults. We report here 2 childhood cases of a cutaneous granular cell tumor.An 8- and a 12-year-old girl, with no past medical history, presented with pigmented nodular lesions located, respectively, in the left scapular region and the left iliac crest. Histological examination showed sheets and clusters of infiltrating tumor cells with morphologic and immunohistochemical features consistent with granular cell tumor. In both cases, the lesions were excised with 2-cm margins. The patients are presently being reviewed at 6-month and 2-month intervals to evaluate for recurrence and any malignant transformation. They were in good health with no signs of further tumor development.GCT is a relatively uncommon benign neoplasm probably of neural origin derived from Schwann cells. The tongue and buccal mucosa are commonly affected. It develops between the second and sixth decades of life, more frequently among women and blacks. It can also occur in childhood, but this is rare. The cutaneous forms, as in the present observations, are exceptional. Benign granular cell tumours are generally seen as a solitary asymptomatic nodule less than 3 cm in size involving the subcutaneous or submucosal tissues. Histologically, the tumor is not encapsulated but is well circumscribed. The tumor cells may show a degree of infiltration of the surrounding connective tissue. The cells are polygonal, have abundant cytoplasm, are granular and weakly eosinophilic. The nuclei are small, vesicular, and highly chromatic. Mitotic figures are rare. A key element for the histological diagnosis is the expression of S100 protein, neuron specific enolase (NSE), and vimentin on immunohistochemistry. The treatment of choice is a conservative surgical excision of the lesion. However, as the GCT has a poorly defined margin, it is suggested that the tumor should be excised along with portions of adjacent tissue. A low rate of recurrence of the lesion has been reported.The specific value of these rare cases is the occurrence in 2 children and the cutaneous location.

International audience; The (e, 3-1e) four-fold differential cross sections (4DCS) are measured for the double ionization of helium in coplanar asymmetric geometry for a wide range of ejected electron energies and at an incident energy of about 600 eV. The experimental angular distributions of the 4DCS are characterized by large angular shifts of the forward and backward lobes with respect to the momentum transfer direction or its opposite, respectively. This validates our previously published results [ Lahmam-Bennani et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 L59 ] which were questioned by Götz et al [ 2003 J. Phys. B: At. Mol. Opt. Phys. 36 L77 ]. A qualitative, kinematical analysis is given which allows relating these shifts and the observed structures in the intensity distributions to the second order, 'two-step 2 ' double ionization mechanism, which is shown to predominate over the first-order 'shake-off ' and 'two-step 1 ' mechanisms under the present kinematics.

Illustrative examples of energy and angular distributions from thee, (3–1)e and (e, 3e) double ionization processes in argon and krypton, at ∼ 5.5 keV impact energy are presented. The relevance of the resulting four-fold and five-fold differential cross sections to the identification of the double ionization mechanism is emphasized.

Electron-impact double ionization of noble gases is investigated theoretically for the case of high incident energies (5 keV). An ab initio calculation is made including partial correlation in the initial state as well as in the final state. The results of the calculations are compared with those of other theories and with the first available (e, 3e) experimental data on krypton 4p 6.

The (e,2e) triple differential cross-sections for ionization of helium leading to the ground ( n =1) and first excited ( n =2) states of the ion are measured under high energy asymmetric Bethe-ridge kinematics, at scattered and ejected electron energies of 5500 and 75 eV respectively. With respect to older experiments, the present data are free from electron distortion effects. Hence, when compared with calculations using different correlated wavefunctions, it is found that the best agreement for the n =1 to n =2 ratio is obtained with the variationally best wavefunction in energy space. This is in contrast with the experimental findings of Cook et al. [J.P.D. Cook, I.E. McCarthy, A.T. Stelbovics and E. Weigold, J. Phys. B, 17 (1984) 2339] and supports the theoretical arguments given by Smith et al. [A.D. Smith, M.A. Coplan, D.J. Chornay, J.H. Moore, J.A. Tossell, J. Mrozek, V.H. Smith, Jr. and S. Chant, J. Phys. B, 19 (1986) 969].

The authors present absolute triple differential cross sections (TDCS) measurements for ionization of helium leaving the ion in both n=1 and n=2 final states, obtained under asymmetric geometry at an incident energy approximately 5.5 keV and ejected electron energies of 5, 10 and 75 eV. The kinematics are chosen to correspond either to a constant ejection energy, or to a constant energy transfer to the target. Angular distributions are measured at both constant ejection angle ( theta a mode) and at constant scattering angle ( theta b mode). In the theta a mode experiments, the momentum transfer dependence of the n=2 triple differential generalized oscillator strength is investigated for the first time. In both modes, the n=2 angular distributions show several new features which are not present for the n=1 ones, and which tend to vanish as the ejected energy is increased. They are attributed to final state interactions between the ejected electron and the excited ion. Comparison with first-order theoretical models shows the inadequacy of a Coulomb wave representation of the ejected electron, while in the R-matrix formalism it is found that a five-state multichannel calculation qualitatively describes the shape (but not the amplitude) of the TDCS measured in the theta b mode. Comparison is also made with the photoionization in the dipolar limit where the momentum transfer approaches zero. When integrated over the ejection direction, the double differential generalized oscillator strength ratio for ionization to the n=1 and n=2 states is found to agree with an earlier first Born close coupling prediction.

Angular correlation measurements of the two final electrons following primary ionization of the Ar(2p) orbital are performed at 2 keV and 3 keV in a wide range of momentum transfer revealing a strong dependence of structural parameters on the kinematical conditions. Characteristic features are a dominant recoil structure at small momentum transfer, a breaking of symmetry around the direction of momentum transfer and a deviation of the recoil peak maximum from the axis of momentum transfer towards smaller deflection angles. The electron momentum density of the Ar(2p) orbital was extracted out of experimental data for the first time. Within experimental errors good agreement was found with results of Hartree-Fock calculations. Extension of the technique of electron momentum spectroscopy performed in slightly asymmetric coplanar kinematics to study electronic structure has been achieved.

The authors report e,(3-1)e experiments for the double ionization (DI) of argon at an incident energy of approximately 5.5 keV. Coincidence angular correlations of the two slow ejected electrons are measured at different ejection energies. The fourfold differential cross section distributions are consistent with a shake-off mechanism for the DI process. The utility of the method is discussed in terms of the different types of mechanisms for DI. A suitable choice of the kinematic parameters may help to identify the DI process. Different successive interactions are discussed which result in double ionization with quite different angular correlations.

Triple differential cross sections measured in a coplanar symmetric geometry on helium and neon at 100 eV and 500 eV incident energy are compared with a distorted-wave Born approximation of Zhang et al. (1989). The agreement is better for 500 eV than for 100 eV and better for helium than for neon. Additionally, measurements on helium at lower energies have been performed. The angular correlations strongly vary with the impact energy. At 500 eV, the peak around 45' which has its origin in binary collisions is largely dominating. With decreasing energy, its relative importance diminishes while the peak around 120' takes over. Both peaks are nearly equal at 50 eV and the distribution reduces to a single peak around 95' at 26.6 eV. There are no theoretical results for comparison at these energies.

The latest, most important developments in (e,2e) studies are reviewed from an experimental point of view. These include ionization processes near threshold, the symmetric energy sharing collisions involving double scattering mechanisms, core states ionization, (e,2e) measurements for autoionizing states and for the simultaneous excitation and ionization of the target. Double ionizing processes with coincidence detection of two or three electrons in the final state are also reviewed, including (e,e'-Auger) experiments and the new born (e,(3-1)e) and (e,3e) domain.

A critical discussion is given of some of the experimental parameters involved in measurement of the three-, four- and five-fold differential cross sections obtained in (e,2e), (e,(3-1)e) and (e,3e) experiments, respectively. Features observed in the triple coincidence time-delay spectrum are attributed to fully accidental, semi-accidental or true triple coincidence events. Formulas are given that allow computation of the true coincidence rate, the percentage statistical error and the signal-to-background ratio, and to optimize the gas density-electron beam current product for any given experiment. The effective coincidence energy resolutions and transmission functions are defined, and their importance clearly demonstrated.

The electron impact outer-shell double ionization of argon has been investigated at 5.5 keV incident energy. (e, (3-1)e) experiments in which two of the three electrons present in the continuum are detected in coincidence have been performed, yielding fourfold differential cross sections. The energy distribution of the two ejected electrons is reported. The observed non-symmetric shape may be attributed to the different angular distribution of the fast and slow ejected electrons.

An extension of the technique of electron momentum spectroscopy (EMS) to study core electronic structures of molecules has been achieved. Measured spherically averaged core electron momentum distributions for three target molecules, nitrogen with symmetry D ∼ h , ethylene with symmetry D 2h and benzene of symmetry C 6h , have been compared with theoretical distributions calculated from SCF wavefunctions, and good agreement has been found. The individual theoretical distributions display quantum interference arising from the multicentred homonuclear nature of the target molecules, and as expected, the hydrogen in ethylene can essentially be neglected in the core, resulting in analogous symmetry structures for nitrogen and ethylene at that level.

A version of the J-matrix method for solving numerically the three-body Faddeev-Merkuriev differential equations is proposed. This method allows to obtain the correlated three charged particle continuum wave function in which two-body subdomains are considered correctly. This function is used for calculations of the fully resolved absolute differential cross sections for double ionization of helium by electron impact. Results are rather close to the experiment.

International audience

A version of the J-matrix method for solving numerically the three-body Faddeev-Merkuriev differential equations is proposed. This version allows one to take into account the full spectrum of the two-body Coulomb subsystem. As a result, a discrete analog of the Lippmann-Schwinger equation is obtained which allows one to interpret correctly the three-body wave function in two-body domains. The scheme is applied to calculations of the fully resolved absolute differential cross sections for the He(e,2e)He{sup +} reactions leaving the residual ion in an excited state, at small energy and momentum transfer. The results are in good agreement with the experiment both in shape and in absolute value.

International audience

International audience

Experimental results obtained with our multi parameter multi-coincidence spectrometer are presented for the (e,3e) double ionisation of Ar and (e,2e) single ionisation of small molecules. The (e,3e) measurements are discussed in terms of competition between the two double ionisation processes present under the chosen kinematics, and qualitative conclusions are given. The results for the ionisation of H2 and the outer orbital of N2 are compared with the predictions of the most elaborate available theoretical models for description of the molecular ionisation process. Overall reasonable agreement is observed and tentative interpretations for the discrepancies are discussed.

We report new coplanar measurements of the (e,2e) TDCS for the ionisation of helium 1s-shell and argon 3p- and 2p-shells. The kinematics employed remained rather unexplored to date, and could be investigated here using an improved version of our multi-angle (e,2e) spectrometer, with increased sensitivity. The results are discussed in the light of state-of-the-art theoretical models.

A multicoincidence electron–electron spectrometer has been modified by including two ion detectors in order to enable both photoelectron–Auger electron and photoelectron (or Auger electron)-ion coincidence measurements as a substantial step towards a complete experiment. Results of the first use of this set-up to study the photoelectron–Auger electron angular correlations and photoelectron angular distributions of “fixed-in-space” molecules in the case of the C 1s ionization of the CO molecule are presented and compared with theoretical calculations in the Hartree–Fock approximation based on the two-step model.

International audience

Measurements of the (e,2e) triply differential cross sections (TDCS) are presented for the ionization of the nitrogen molecule in coplanar asymmetric geometry at an incident energy of about 600 eV and a large energy transfer to the target. The experimental results are compared with state-of-the-art available theoretical models for treating differential electron impact ionization of molecules. The experimental TDCS are characterized by a shift towards larger angles of the angular distribution with respect to the momentum transfer direction, and by a large intensity in the recoil region, especially for ionization of the ‘inner’ 2σ g molecular orbital. Such shifts and intensity enhancement are not predicted by the model calculations which rather yield a TDCS symmetrically distributed around the momentum transfer direction. (Some figures in this article are in colour only in the electronic version)

The (e,3e) angular distributions for the double ionisation of Ar where at least two of the three outgoing electrons have the same kinetic energy (205 eV) as the Auger electron issued from a 2p‐ionisation and the subsequent electronic relaxation have been theoretically investigated at three different impact energies within a first Born model and including electron exchange and interference of processes. The results are compared with recent (e,3‐1e) measurements under the same kinematics. Possible dominant ionisation mechanisms are tentatively identified in each case.

International audience

International audience

In this Comment, we question the recent analysis of (e,3e) experimental data obtained on He presented by Dorn et al. [Phys. Rev. A 68, 012715 (2003)]. The authors claimed to observe 'a new, somewhat unexpected effect', namely the 'disappearance' of the second Born effects at large momentum transfer (q{approx}2 a.u.) to the target. Here we show that their claim is not supported by their data. We argue that these data are consistent with strong deviations from the first Born regime, quite similar to the deviations observed at small momentum transfer (q{approx}0.7-0.9 a.u.)

We present a new, unprecedented electron impact (e,3–1e) study of the ionization of the 2p-inner shell of argon. For the first time, multi-angular distributions are measured for the coincidence detection of two electrons emitted with the same kinetic energy (205 eV) as the Auger electron issued from the electronic rearrangement of the target. The incident energy is chosen such as to leave the third, unobserved electron with either a small or a large kinetic energy, or else with the same energy of 205 eV. In the latter case, the three final state electrons are fully indistinguishable (or at 'resonance'). A rich structure is observed in the angular correlation diagrams. At the highest energy, the observed pattern may qualitatively be explained by considering the Auger emission as a 2-step process. At lower energies, and in particular when all three outgoing electrons have identical energies, the picture dramatically changes, bearing almost no trace anymore of the 2-step process, and being very likely dominated by strong interference and post collisional interaction effects.