Physical Review B

Cold Target Recoil Ion Momentum Spectroscopy: a &momentum microscope' to view atomic collision dynamics

One of the most significant developments in computational atomic and molecular physics in recent years has been the introduction of B-spline basis sets in calculations of atomic and molecular structure and dynamics. B-splines were introduced in applied mathematics more than 50 years ago, but it has been in the 1990s, with the advent of powerful computers, that the number of applications has grown exponentially. In this review we present the main properties of B-splines and discuss why they are useful to solve different problems in atomic and molecular physics. We provide an extensive reference list of theoretical works that have made use of B-spline basis sets up to 2000. Among these, we have focused on those applications that have led to the discovery of new interesting phenomena and pointed out the reasons behind the success of the approach.

https://iopscience.iop.org/article/10.1088/0034-4885/64/12/205/pdf

Applications of B-splines in atomic and molecular physics

High-resolution recoil-ion momentum spectroscopy (RIMS) is a novel technique to determine the charge state and the complete final momentum vector of a recoiling target ion emerging from an ionizing collision of an atom with any kind of radiation. It offers a unique combination of superior momentum resolution in all three spatial directions of with a large detection solid angle of . Recently, low-energy electron analysers based on rigorously new concepts and reaching similar specifications were successfully integrated into RIM spectrometers yielding so-called `reaction microscopes'. Exploiting these techniques, a large variety of atomic reactions for ion, electron, photon and antiproton impact have been explored in unprecedented detail and completeness. Among them kinematically complete experiments on electron capture, single and double ionization in ion - atom collisions at projectile energies between 5 keV and 1.4 GeV have been carried out. Double photoionization of He has been investigated at energies close to the threshold up to . At the contributions to double ionization after photoabsorption and Compton scattering were separated kinematically for the first time. These and many other results will be reviewed in this paper. In addition, the experimental technique is described in some detail and emphasis is given to envisaging the rich future potential of the method in various fields of atomic collision physics with atoms, molecules and clusters.

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Recoil-ion momentum spectroscopy

The neutralization of highly charged ions during interaction with metallic surfaces is accompanied by the ejection of a large number of secondary electrons Recent experiments demonstrate two main contributions to this electron ejection process: one from the region below the surface and the second from the above-surface portion of the trajectory We present a theoretical analysis of the neutralization dynamics above the surface, prior to impact, based on the classical over-the-barrier model The theory incorporates resonant multielectron capture of conduction electrons, resonant loss into unoccupied states of the conduction band, and intra-atomic Auger deexcitation The effective barrier potential includes quantum corrections to the classical image potential The effect of below-barrier (``tunneling'') transfer is investigated The solution of a coupled system of rate equations allows the approximate determination of the n-shell populations, the projectile charge state, and the total number of Auger electrons The calculation describes the transient formation of ``hollow'' atoms We find satisfactory agreement with recent data for K Auger yields by Meyer et al [Phys Rev Lett 67, 723 (1991)]

Above-surface neutralization of highly charged ions: The classical over-the-barrier model

Interaction of slow multicharged ions with solid surfaces

The status of our knowledge an the mechanisms of multiple captures by a highly cnargsu iuii cuin~umg wiin an aiom IS ~CYITWTU. 1 ne various and compiemeniary techniques are first described, including energy gain spectroscopy, electron and photon spectroscopy with a particular emphasis on the rapidly developing techniques combining these spectras- copies in coincidence experiments. The double capture processes are simple enough to allow theoretical calculations and a detailed analysis of capture mechanisms wch as the relative role of the electron-nucleus interaction and the electron-electron interaction. This is not yet the case far multiple captures, which imply a very large number of channels. However the simple classical overbarrier modeli in its extended form, is able to account lor the gross features of multiple capture processes such as the number of electrons stripped lrom the target. However, such models are often unable to predict the number of electrons actually captured by the projectile. This is due to the role played by the electron-electron interaction in the population and decay of multiply excited configurations with equivalent and non-equivalent electrons.

http://iopscience.iop.org/article/10.1088/0953-4075/25/10/006/pdf

Multiple electron capture by highly charged ions at keV energies

We present evidence for the diffraction of light keV atoms and molecules grazingly scattered on LiF(001) and NaCl(001) surfaces. At such energies, the de Broglie wavelength is 2 orders of magnitude smaller that the mean thermal atomic displacement in the crystal. Thus, no coherent scattering was expected and interaction of keV atoms with surfaces is routinely treated with classical mechanics. We show here that well-defined diffraction patterns can be observed indicating that, for grazing scattering, the pertinent wavelength is that associated with the slow motion perpendicular to the surface. The experimental data are well reproduced by an ab initio calculation.

Quantum scattering of fast atoms and molecules on surfaces.

Impact of 600 eV protons at grazing incidence on LiF(100) is studied with a new coincidence technique combining energy loss and electron spectroscopy. Correlation between the secondary electrons and the charge state of the scattered projectiles demonstrates the role of the ${\mathrm{H}}^{\ensuremath{-}}$ ions formed on the surface as precursors for electron emission. However, the main channel for energy loss is not associated with electron emission but is interpreted as the population of surface excitons.

/pdf/energy-loss-of-low-energy-protons-on-lif-100-surface-10n30860ne.pdf

Energy Loss of Low Energy Protons on LiF(100): Surface Excitation and H − Mediated Electron Emission

Diffraction of fast atoms at grazing incidence has been recently demonstrated on the surface of alkali halides and wide band gap semiconductors, opening applications for the online monitoring of surface processes such as growth of ultrathin layers. This Letter reports energy resolved diffraction of helium on Ag(110) metal surface showing that a band gap is not mandatory to restrict the decoherence due to electron-hole pair excitations by the keV projectile. Measurement of the energy loss, which is in the eV range, sheds light on the scattering process.

Philippe Roncin

Papers

Interaction of slow multicharged ions with solid surfaces

Multiple electron capture by highly charged ions at keV energies

Quantum scattering of fast atoms and molecules on surfaces.

Energy Loss of Low Energy Protons on LiF(100): Surface Excitation and H − Mediated Electron Emission

Grazing incidence diffraction of keV helium atoms on a Ag(110) surface.