http://www.primefan.ru/stuff/chem/lamb.pdf

The lamb shift in hydrogen-like atoms, 1 ⩽ Z ⩽ 110

The series Lecture Notes in Chemistry (LNC), reports new developments in chemistry and molecular science quickly and informally, but with a high quality and the explicit aim to summarize and communicate current knowledge for teaching and training purposes. Books published in this series are conceived as bridging material between advanced graduate textbooks and the forefront of research. They will serve the following purposes:  • provide an accessible introduction to the field to postgraduate students and nonspecialist researchers from related areas, • provide a source of advanced teaching material for specialized seminars, courses and schools, and • be readily accessible in print and online. The series covers all established fields of chemistry such as analytical chemistry, organic chemistry, inorganic chemistry, physical chemistry including electrochemistry, theoretical and computational chemistry, industrial chemistry, and catalysis. It is also a particularly suitable forum for volumes addressing the interfaces of chemistry with other disciplines, such as biology, medicine, physics, engineering, materials science including polymer and nanoscience, or earth and environmental science.  Both authored and edited volumes will be considered for publication. Edited volumes should however consist of a very limited number of contributions only. Proceedings will not be considered for LNC.  The year 2010 marks the relaunch of LNC.

Lecture notes in Chemistry

Radiative electron capture in relativistic ion–atom collisions and the photoelectric effect in hydrogen-like high-Z systems

Collisions of very heavy ions at energies close to the Coulomb barrier are discussed as a unique tool to study the behavior of the electron-positron field in the presence of strong extemal electromagnetic fields. To calculate the excitation processes induced by the collision dynamics, a semiclassical model is employed and adapted to describe the field-theoretical many-particle system. An expansion in the adiabatic molecular basis is chosen. Energies and matrix elements are calculated using the monopole approximation. In a supercritical (2, + Z, 2 173) quasiatomic system the 1s level joins the antiparticle continuum and becomes a resonance, rendering the neutral vacuum state unstable. Several methods of treating the corresponding time-dependent problem are discussed. A projectionOperator technique is introduced for a fully dynamical treatment of the resonance. Positron excitation rates in s„, andp,,] states are obtained by numencal solution of the coupled-channel equations and are compared with results from first- plus second-order perturbation theory. Calculations are performed for subcritical and supercritical collisions of Pb-Pb, Pb-U, U-U, and U-Cf. Strong relativistic deformations of the wave functions and the growing contributions from inner-shell bound states lead to a very steep Z dependence of positron production. The results are compared with available data from experiments done at GSI. Correlations between electrons and positrons are briefly discussed.

/pdf/theory-of-positron-production-in-heavy-ion-collisions-4u32kfjsee.pdf

Theory of positron production in heavy-ion collisions

Electron–ion collisions are among the most important atomic processes in ionized gases. They comprise elastic scattering, excitation, ionization, and recombination. Theoretical approaches are numerous but calculating reliable results for applications is a task that has not generally been solved, although theory has progressed considerably in the last decade and can now provide reference data for electron collisions with few-electron systems. Experimental data on electron–ion collisions can be inferred from plasma observations, from ion trap measurements, from careful preparation and analysis of ion–atom collisions, and from colliding-beams experiments. The spectrum of equipment employed in the measurements ranges from table top size to large accelerator and storage-ring facilities. This article provides an overview of the processes involved in electron–ion collisions, their cross sections, the experimental approaches and typical results. The present status of the field is discussed and characterized by numerous examples illuminating the accomplishments as well as the limitations of experimental access to accurate detailed cross sections and rate coefficients, as they are required for understanding and modelling laboratory or astrophysical plasmas.

Electron–ion collisions: Fundamental processes in the focus of applied research

Electron-electron interaction is studied in the strongest possible atomic fields $(Z\ensuremath{\alpha}\ensuremath{\Rightarrow}1)$ in the presence of only two electrons. A quasifree electron from a hydrogen gas target is resonantly captured into an ${L}_{j}$ subshell of a fast H-like ${\mathrm{U}}^{91+}$ ion by simultaneous excitation of the strongly bound $K$ electron also into an ${L}_{{j}^{\ensuremath{'}}}$ subshell of the projectile, with $j$ and ${j}^{\ensuremath{'}}$ the total angular momenta of 1/2 or 3/2 for the electron of concern. This resonant transfer and excitation process (RTE) ${\mathrm{KL}}_{j}{L}_{{j}^{\ensuremath{'}}}$ is mediated by electron-electron interaction. It is equivalent to dielectronic recombination in ion-electron collisions and leads to a doubly excited He-like ${\mathrm{U}}^{90+**}$ ion, which stabilizes---almost exclusively---via the emission of two successive $K$ x rays, first a $K$ hypersatellite $(K{\ensuremath{\alpha}}_{i}\ensuremath{-}H)$ and then a $K$ satellite $(K{\ensuremath{\alpha}}_{{i}^{\ensuremath{'}}}\ensuremath{-}S)$ transition. The $K$ x-ray emission characteristics associated with one-electron capture in collisions of ${\mathrm{U}}^{91+}$ ions with a hydrogen target are studied for the three resonance groups of the ${\mathrm{KL}}_{j}{L}_{{j}^{\ensuremath{'}}}$ RTE and one off-resonance energy, i.e., in the energy range between 100 and 135 MeV/u. The total cross section for the first resonance group ${\mathrm{KL}}_{1/2}{L}_{1/2}$ confirms the importance of the Breit contribution to the interaction. The angular distribution for the $K{\ensuremath{\alpha}}_{2}\ensuremath{-}H$ transition $(j=1/2)$ is isotropic in the projectile system, whereas the $K{\ensuremath{\alpha}}_{1}\ensuremath{-}H$ transition $(j=3/2)$ indicates a strong alignment for the 3/2 electrons in the doubly excited states for the second resonance group ${\mathrm{KL}}_{1/2}{L}_{3/2}.$ The experimental results are in agreement with fully relativistic calculations including the generalized Breit interaction.

/pdf/electron-electron-interaction-studied-in-strong-central-3xx1khlkpq.pdf

Electron-electron interaction studied in strong central fields by resonant transfer and excitation with H-like U ions

Hydrogenlike and heliumliken=2→n=1 lines in Kr have been produced and studied for the first time. HydrogenlikeL y α lines have been observed and the fine structure interval has been determined. The absolute energy of the1P1,3P2,3P1 lines of heliumlike Kr have been measured and compared to Multiconfigurational Dirac-Fock Calculations.

Observation of hydrogenlike and heliumlike krypton spectra

From 90° line width analysis ofKα1 lines excited in very heavy ion-atom collisions (Z1 +Z2>137) mean impact parameters for the ionization probability are derived. The experimental mean impact parameters are shown to obey the Bang-Hansteen scaling rule¯bE(R)=C · ħv correlating the minimum momentum transferE(R)/v and the mean impact parameterb. Theoretical values of the constantC are (0.8±0.1) for 2p1/2σ excitation and (1.0±0.1) for 1sσ excitation in the rangeZ1+Z2=140–160. It is proposed to apply the scaling rule as a spectroscopic tool to study the 1sσ and 2p1/2σ levels in superheavy quasimolecules. The need of a sound theoretical base justifying the application of the scaling rule is emphasized.

A tool for spectroscopy of super-heavy quasimolecules (Z 1+Z 2>137) the Bang-Hansteen scaling rule

Using particle x-ray coincidence techniques, the probability to produceK-shell vacancies in 4.7 MeV/u Pb+Z2 (42≦Z2≦92) collisions for impact parametersb<100 fm was measured. For these impact parameters, the 1sσ excitation probability is greater than 1 σ 10−2 and the 2p1/2σ excitation probability is greater than 1 σ 10−1. Binding energies of the 1sσ state derived from the measured probabilities agree well with theoretical calculations.

Measurements of the probability for 1 sσ excitation in very heavy ion-atom-collisions and determination of the binding energy of the 1 σ molecular orbital

Using particle x-ray coincidence techniques, the probability forK shell ionization has been measured absolutely at two impact parameters for collisions of 5.8 MeV/amu208Pb on Ag and Au. In the asymmetric collision system Pb-Ag, the 1sσ excitation probability of the PbK shell is 2.2% at 25 fm impact parameter, and an exponential probability distribution falls off too quickly to account for the measured total cross section. For the symmetric system Pb-Au, the latter conclusion is also made for the 2pσ excitation probability although in this case, the probability is much larger being 29% at 42 fm.

D. Liesen

Papers

Electron-electron interaction studied in strong central fields by resonant transfer and excitation with H-like U ions

Observation of hydrogenlike and heliumlike krypton spectra

A tool for spectroscopy of super-heavy quasimolecules (Z 1+Z 2>137) the Bang-Hansteen scaling rule

Measurements of the probability for 1 sσ excitation in very heavy ion-atom-collisions and determination of the binding energy of the 1 σ molecular orbital

An absolute measurement of the probability for 1 s σ and 2 p σ excitation of the lead K shell