X ray spectroscopic intercomparison between hydrogenic ions of different Z as a method for determining Lamb shifts

Novel methods for determining the 1s Lamb shift of hydrogenic ions are outlined. In one method the energy of a 2–1 transition in the hydrogenic ion of nuclear charge Z is compared to a 4–2 transition in the hydrogenic ion of charge 2Z. A second method exploits close coincidences between Lyman series transitions in ions of similar Z. This revised version was published online in August 2006 with corrections to the Cover Date.     

Measurement of the gj factor of hydrogenic ions: a sensitive test of bound state QED

Theg _j factor measurement of hydrogenic ions in the 1s ground state is with an expected accuracy of 10^–7 a sensitive test of bound state QED. We expect to determine the deviations from the free electron value, caused by relativistic and radiative corrections, up to the order/4(Z) ² with an accuracy of 1%. As a first step, light ions like C⁵⁺ will be investigated. Later on, heavier hydrogenic ions up to U⁹¹⁺ will be examined using the accelerator facilities at GSI in Darmstadt.     

Effect of conduction band parabolicity on the spectrum and binding energy of a hydrogenic impurity in GaAs spherical quantum dots

The energy levels and binding energies of a hydrogenic impurity in GaAs spherical quantum dots with radius R are calculated by the finite difference method. The system is assumed to have an infinite confining potential well with radius R, which can be viewed as a hard wall boundary condition. The parabolicity of the conduction band profile for GaAs material can be viewed as a parabolic potential well. The energy levels and binding energies are depended dramatically on the radius of the quantum dot and the parabolic potential well. The results show that parabolic potential can remarkably alter the energy level ordering and binding energy level ordering of hydrogenic impurity states for the quantum dot with a smaller radius R.     

Relativistic correction to the dipole polarizability of a hydrogenic ion

The first relativistic correction of orderα ² to the dipole polarizability of a hydrogenic ion has been investigated by using mean excitation energy of the ion within the second-order perturbation theory. The density-dependent mean excitation energy is estimated via Bethe theory for the stopping cross section for a moving point charge interacting with the hydrogenic ion. In this approach only the unperturbed Dirac wavefunctions are required to evaluate the appropriate matrix elements. The first relativistic correction turns out to be − (13/12)(αZ)². This has the correct sign and is within 5% of the exact result which is −(28/27)(αZ)².     

A Variational Wave Function for 2p2-Orbitals in Atomic Negative Ions

A variational wave function is used to describe the binding energy of atomic negative ions using a two-electron system in the 2p²-state. Each electron is described by a modified screened hydrogenic wave function involving two free screening parameters denoted by c and a. The model is applied to hydrogen, helium, lithium, and boron anions, where the optimum values of the screening parameters are deduced through fitting the optimized energy to available experimental and theoretical values. The behavior of the optimum wave function for each anion is also investigated as a function of electronic radial distance and compared with its counterpart in the screened hydrogenic model and the Hartree–Fock method.     

Diamagnetic susceptibility of hydrogenic donor impurity in low-dimensional semiconducting systems

The binding energies of a hydrogenic donor both in the parabolic and non-parabolic conduction band model within the effective mass approximation have been computed for the low-dimensional semiconducting systems (LDSS) like quantum well, quantum well wire and quantum dot taking GaAs/Al_xGa_1−xAs systems as an example. It is observed that the effect of non-parabolicity is not effective when the system goes to lower dimensionality. The diamagnetic susceptibility of a hydrogenic donor impurity has also been computed in these LDSS in the infinite barrier model. Since no theoretical or experimental works on the diamagnetic susceptibility of LDSS are available in the literature, as a realistic case the diamagnetic susceptibility has been computed in the finite barrier model (x=0.3) for a quantum well and the results are discussed in the light of semiconductor-metal transition.     

Effect of distortion in electron impact excitation in Coulomb-projected Born approximation

We have calculated total and differential cross-sections for 1s →ns (n = 2, 3, 4) electron impact excitation of hydrogen and hydrogenic ions at various energies in Coulomb-projected Born approximation. Distortion due to static interactions, target polarization and exchange effects has been incorporated in the initial channel. The present calculations have been compared with other theoretical and experimental results.     

Electron Spin–Nuclear Spin Cross-Correlation Effects on Multiplet Splittings in Paramagnetic Proteins

The effects of cross-correlation between Curie spin–nuclear dipole and nuclear dipole–nuclear dipole interactions on the linewidths and resonance frequencies of the individual lines of anAXmultiplet in paramagnetic systems have been calculated. The implication of the relaxation-induced frequency shift of the lines (dynamic frequency shift) for the accurate measurement of residual dipolar couplings in field-oriented systems has been discussed. Our simulations indicate that these effects may play a role in the precise measurement of residual dipolar couplings in systems which belong to the small and intermediate tumbling regime, i.e., correlation times less than 5 ns.     

Soft X-ray gain in hydrogenic ions: Line pumping,ionization pumping and transient excitation

In a plasma containing hydrogenic ions which is irradiated by appropriate X-ray radiation, gain on the n=3n=2 (Balmer-) transition can be generated. Depending on the spectrum of the pump radiation, there are two different ways of obtaining the inversion: direct excitation of the upper laser level by line radiation, or ionization of the hydrogenic ions by broad band radiation with subsequent population of the upper level by recombination.In the first part of this paper, we present numerical calculations which compare the two pumping methods. The gain is evaluated under idealized conditions, i.e., with a pump spectrum containing only radiation useful for generating an inversion and under more realistic conditions, with a pump spectrum containing radiation at other frequencies as well.In the second part of the paper the possibility of obtaining Balmer- gain in hydrogenic ions under highly transient conditions is investigated, assuming a pump pulse with a duration comparable to the decay time of the lower laser level. Considerable gain is predicted even for a black-body pump spectrum.     

Features of the bremsstrahlung accompanying collisions with a hydrogen atom in an excited state

The features of the bremsstrahlung appearing during a collision of a fast charged particle with a hydrogen atom (or hydrogenic ion) in an excited state are investigated. It is shown that the emission spectrum of photons with energies greater than the ionization potential of a given excited state (except the 2s state) displays narrow lines, which are caused by de-excitation of the atom in an intermediate state. It is demonstrated that the scattering of a charged particle on an excited hydrogen atom produces a feature which is not observed in the case of scattering on a ground-state hydrogen atom. Expressions are obtained for the generalized dynamic polarizability of the hydrogen atom and hydrogenic ions in the 1s, 2s, and 3s states. A method is developed for deriving expressions for the generalized dynamic polarizabilities of other excited states through the use of the Coulomb Green’s function and representation of the electronic wave function in terms of the differentiation of the generating functions of Laguerre polynomials. The bremsstrahlung cross sections for electrons and positrons colliding with hydrogen atoms in the 1s, 2s, and 3s states are calculated. Zh. Tekh. Fiz. 69, 7–13 (October 1999)     

Radiative frequency shift without ultraviolet divergency in a two-level hydrogenic atom

Summary By taking into account the retardation effects a finite result for the frequency shift of the Lyman α-radiation from a two-level hydrogenic atom is obtained. This result shows a nonnegligible correction as compared to previous results obtained in the dipole approximation with a cut-off frequency.     

High-lying doubly excited states of He and H<Superscript>−</Superscript>: electron correlations and classification schemes

High-lying doubly excited states of He and H⁻ are studied and energies and intrinsic characteristics of their wave-functions are reported. Results for energies of ³P ^o and ¹D doubly excited states associated with the hydrogenic thresholds up to N = 20 are presented and compared to available data from the literature. The classification of these doubly excited states by approximate quantum numbers is reexamined.     

Collision strengths for the N = 2 excitation of hydrogenic ions

An empirical formula is given for the estimation of the collision strengths for electron impact excitation of the 2s and 2p states of hydrogenic systems based on close coupling calculations. The coefficients in this formula are given as functions of the nuclear charge, Z, thereby making a possible estimation of the collision strength for any system between H and Fe²⁵⁺.     

Electron Correlations and Classification Schemes for Intershell Doubly Excited States

High-lying intershell doubly excited states of He and H⁻ are studied and energies and intrinsic characteristics of their wave functions are reported. Results for energies of ³S and ¹P^e doubly excited states associated with the hydrogenic manifold up to N = 20 are presented and compared to available data from the literature. The classification of these doubly excited states by approximate quantum numbers is reexamined.     

Electron shake process following inner‐shell ionization

Electron shakeup and shakeoff probabilities accompanying inner‐shell ionization of atoms were calculated for K‐, L‐ and M‐shell electrons using hydrogenic wavefunctions. The dependence of shake probabilities on atomic number Z is estimated. It is found that both shakeoff and shakeup probabilities are proportional to 1/Z². Based on this Z‐dependence, the shakeup‐plus‐shakeoff probabilities are expressed in a simple analytical form with two parameters. Copyright © 2004 John Wiley & Sons, Ltd.     

Polarizability of a hydrogenic donor impurity in a ridge quantum wire

We use in this paper the variational method to calculate the polarizability of a hydrogenic donor impurity, in the presence of electric field, in a V-groove GaAs/Al_xGa_1−xAs quantum wire. The carrier ground states are analytically obtained by an effective potential scheme together with a suitable coordinate transformation that allows the decoupling of the two-dimensional Schrodinger equation. According to the results obtained from the present work for polarizability and binding energy reveals that the impurity position and field direction play important roles.     

Thermal diffusion factors of hydrogenic trace mixtures with helium by column calibration factor

Using column calibration factor (CCF)F _s for a given column, the temperature dependence of experimental thermal diffusion factors α_T of hydrogenic trace mixtures in helium are accurately determined. This study, however, observes the inelastic collision effect in these trace mixtures when α_T by our CCF method are compared with those by the existing methods and theoretical ones respectively.     

Differential elastic cross-sections of excited exotic hydrogen atoms

Differential cross-sections for the elastic scattering of excited exotic hydrogen atoms by hydrogenic atoms are calculated for the first time. The calculations are performed for exotic atoms (μ a,π a; a=p,d,t) in the states with the principal quantum numbers n=2-10 at relative motion energies E=0.001-15 eV and at scattering angles ϑ =0–180^00B0;. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nonperturbative gluoproduction versus perturbative QCD fusion models for heavy quark production

Technicolor (hypercolor, etc.) theories of the strong and electro-weak interactions predict the existence of stable charged particles with masses greater than 10³ GeV/c². We point out that hydrogenic bound states of such stable particles and electrons may be detectable in current spectral data due to the mass dependence of hydrogenic energy levels.     

Influence of surface electric fields on the alignment of the hydrogen-2p state after beam-foil-excitation

In contrast to other atomic systems, foil excited hydrogen or hydrogen-like atoms show a negative alignment for various energy ranges. We suggest that this particular behaviour results from the degeneracy of differentL states in hydrogenic systems and an observable influence of a surface electric field modifying the initial alignment via Stark effect.