Hydrogenic atoms in “superstrong” magnetic fields

An estimate is made of the magnetic field above which many recent non-relativistic treatments of hydrogenic atoms in strong magnetic fields become invalid. It is argued that this value may be as low as 10¹⁰Z Gauss.     

Observation of giant polarizabilities in atomic sodium Rydberg states

We have observed by quantum beat spectroscopy the Stark effect in a low electric field of highly excited Na nD states (n = 10, 11, 12). The polarizabilities are found to be 10⁶ to 10⁷ time larger than those of atoms in ground or low lying excited states and are in good agreement with theoretical values calculated from a hydrogenic model.     

Observation of highly ionised species in plasma produced by picosecond laser pulses

Results are presented which show that in the case of the light elements highly ionised species can be detected in laser produced plasmas using a normal incidence spectrograph, the plasmas being formed by picosecond pulses from a high power Nd: glass laser. In particular hydrogenic ions of carbon, oxygen and fluorine have been observed when the incident laser flux density onto a solid target was about 3×10¹⁴W/cm².     

Electron state density and electron diffusion coefficient in energy space in nonideal nonequilibrium plasmas

We suggest a model for a hydrogenic low-temperature nonequilibrium nonideal plasma that allows the kinetic parameters of the plasma to be calculated by the method of molecular dynamics by taking into account the interparticle interaction. The charges interact according to Coulomb’s law; for unlike charges, the interaction is assumed to be equal to a constant at a distance smaller than several Bohr radii. For a system of particles, we solve the classical equations of motion under periodic boundary conditions. The initial conditions are specified in such a way that the electrons have a positive total energy. We consider the temperatures 1-50 K and densities n = 10⁹?10¹⁰ cm^?3 produced in an experiment through laser cooling and resonant excitation. We calculate the electron state density as a function of the plasma coupling parameter and the electron diffusion coefficient in energy space for highly excited (Rydberg) electron states close to the boundary of the discrete and continuum spectra.     

Magnetic circular dichroism of band-edge exciton absorptions in PbI2

The linear Zeeman behaviour of the n = 1, 2 and 3 exciton absorptions near 20000 cm^-1 in PbI₂ single crystals was determined from measurements of the magnetic circular dichroism. The similarity of the g-value (+ 1.5 ± 0.5) for each of the n = 1, 2 and 3 lines supports the hydrogenic model. Any quadratic shifts of the n ? 2 levels were < 10 cm^-1 in an applied magnetic field of 21 T.     

High resolution spectroscopy of rydberg states in indium I

Two-photon laser spectroscopy in a dense indium vapour allowed to investigatenp ² P _{1/2, 3/2} states (n=27–35) for^{113, 115}In with a thermionic diode. Precise data on the fine structure splitting of these states and the isotope shift of the two photon transitions have been obtained. The fine structure splitting shows a hydrogenic behaviour. By using the result of our isotope shift measurement in combination with literature values, level isotope shifts with reference to the ionization limit are deduced and analysed with respect to the different contributions.     

Initial population ofμ −,π −,K − after radiative atomic recombination

We calculate the radiative atomic recombination ofμ ^?,π ^?,K ^? with a nucleus. In the initial state the negative particle moves in a Coulomb field, in the continuous spectrum, with positive energy and is captured into the bound orbit (n,l) of negative energy. We consider the exotic atom as a hydrogenic atom. The analytical expression of the recombination cross section, together with a “low energy” approximation, is derived. We obtain information on the atomic initial population: the results presented here show that the Bohr statistical distribution, used in the case of neutral atoms, is not correct in this case.     

Hydrogenic Impurity States in a Quantum Pseudodot: Spin-Orbit Interaction, Relativistic Correction, and Diamagnetic Susceptibility

We have studied three characteristics of a hydrogenic impurity located in the center of a quantum pseudodot within the effective mass approximation. These characteristics are the diamagnetic susceptibility, the spin-orbit interaction (SOI), and the relativistic correction (RC). First, we have solved analytically the Shrödinger equation without impurity by using the Laplace transformation. Then, we have applied the variational procedure to obtain energy levels and wave functions with a hydrogenic impurity in the center of quantum pseudodot. According to the results obtained from the present work reveals that (i) the diamagnetic susceptibility increases with increasing the pseudodot size, (ii) The mean value of r ² increases when the pseudodot size increases, (iii) the SOI and RC increase by increasing the potential V ₀, (iv) the RC and SOI approach to zero when the pseudodot increases, (v) the splitting between j=1/2 and 3/2 due to the SOI decreases by increasing pseudodot size.     

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⁺.     

The photodisintegration of6Li and7Li

The photodisintegration of the stable Lithium isotopes has been investigated by spectroscopy of the emitted charged particles using the Giessen bremsstrahlung facility. Protons, deuterons, tritons,³He and alpha particles were detected and identified up to 20MeV particle energy. Angular distributions were measured using γ-ray energies up toE _γ =50 MeV. They are compared with theoretical predictions and with other experiments. A remarkable low (γ, t)-cross section was found for both isotopes in disagreement to previous measurements using virtual photons. Coincidence measurements between the emitted particles were performed in order to study the manybody-breakups of⁷Li.     

Exact polarizability of low-dimensional excitons

Wannier excitons polarized by a static electric field and confined to low-dimensional structures are studied. Effective non-integer dimensions are included by considering hydrogenic states in α-dimensional space, with α as a parameter. Exact expressions for lowest order energy and wave function corrections are obtained as a function of α. For the 1s state, we demonstrate that the exciton polarizability decreases with reduced dimensionality and eventually vanishes as (α−1)⁴ as the 1D limit is approached. The low-dimensional 2s and 2p polarizabilities are also decreased but remain finite in the 1D limit.     

Nuclear finite-size effects in light muonic atoms

The finite nuclear size corrections to the s-state energy levels of light muonic (or hydrogenic) atoms are calculated analytically through order (Zα)⁶. In addition to the usual expression of order (Zα)⁴, the (Zα)⁵, (Zα)⁶ and (Zα)⁶ log(Zα) contributions have been determined. These corrections have been separated into terms of nonrelativistic and relativistic orders. The results have been checked by solving perturbatively the exact eigenvalue equations of the Schroedinger and Dirac problems of a particle orbiting in the Coulomb field of a uniform charge distribution of fixed radius. Application is made to the case of the μ-⁴He atom. Finite-size contributions to the hydrogen Lamb shift and the relativistic recoil effect are briefly discussed.     

K X-ray transition energies for first row atoms and ions

X-ray energies are computed using screened, hydrogenic Slater integrals for all configurations [(1s^l2s^m2pⁿ) with l = 0 and 1, m = 0, 1, and 2, and n = 1 through Z-4] of all ionization stages of the elements boron through neon. The results include diagram lines, satellite lines, hypersatellite lines, and two-electron, one-photon lines. Excellent agreement is found between these results and those found by the Hartree-Fock-Slater method. In addition, X-ray energies associated with the spin-orbit forbidden decay of n = 2 three-electron quartet terms and four-electron quintet terms are calculated for the elements beryllium through neon. These results agree closely with those found by 1/Z perturbation theory.     

High magnetic field studies of donor excitation spectra in InSb

The two lowest energy spectral lines of the shallow donors in InSb involving ground to excited state transitions are studied in photoconductivity using higher spectral resolution and stronger magnetic fields than achieved previously. The observed line positions are compared with recent calculations of the high field hydrogenic donor levels and difference of the order of the effective Rydberg R¹ at zero field are found at magnetic fields where the zero point cyclotron energy exceeds R¹ by two orders of magnitude. Central-cell components of the 1s–2p transition, corresponding to four donor species are resolved, and the magnetic field dependence of the relative chemical shifts are analysed. The broader 1s–2p₀ line undergoes a coupling at an interaction energy of 37 cm^-1, the origin of which is uncertain at present.     

Early building up of the quasi Landau spectrum in the diamagnetic coulomb region

We report the results of experimental measurements on atomic diamagnetism in inter-l and inter-n mixing conditions. They have been obtained using high resolution techniques on highly hydrogenic M = ± 3 states of cesium, providing a pure experimental situation. Comparison with straightforward hydrogenic calculations and semi-classical predictions allow identification of the dominant lines of the spectrum which are shown to behave as precursors of the quasi Landau spectrum.     

The stability boundary of four-particle mesomolecules

Multiparametric variational calculations of the ground-state energy of symmetric four-particle mesomolecules of the type X ⁺ Y ⁺ X ^? Y ^? as a function of masses M and m of particles X and Y are carried out. A basis consisting of 3200 Gaussian functions depending on all six interparticle distances is used. Calculations are carried out with the optimization of 1200 nonlinear parameters of the first 200 basis functions. As opposed to mesomolecules of the type X ⁺ X ⁺ Y ^? Y ^?, which are stable for all values of masses M and m in X ⁺ Y ⁺ X ^? Y ^? systems, are stable with respect to dissociation if the ratio of the masses of particles X and Y in them satisfies the condition 0.472≤M/m≤2.12. Hence it follows that four symmetric mesomolecules of the type considered (π⁺μ ⁺π^?μ^?, t ⁺ d ⁺ t ^? d ^?, p ⁺ K ⁺ p ^? K ^?, and d ⁺ p ⁺ d ^? p ^?) and 84 various asymmetric mesomolecules of the type X ⁺ Y ⁺ Z ^? T ^? are knowingly stable with respect to dissociation. For mesomolecules of the type X ⁺ Y ⁺ X ^? Y ^?, which are stable with respect to dissociation, mathematical expectations of their physical quantities depending on interparticle distances that specify averaged geometrical structures of these systems are calculated and their dependence on the masses of particles M and m is studied.     

Rayleigh-Schrödinger perturbation theory at large order for radial relativistic Hamiltonians using hypervirial and Hellmann-Feynman theories

Relativistic hypervirial and Hellmann-Feynman theorems are used to construct Rayleigh-Schrödinger expansions for eigenvalues of perturbed radial Dirac equations to aribitrary order. The method is very simple and flexible, requiring no matrix elements. Only the unperturbed energy is required as input. Any difficulties due to the presence of unperturbed continuum states are bypassed. Particular attention is paid to hydrogenic atoms with confining scalar potentials of the form W(r) = λr^q, q = 0, 1, 2, …. Continued fraction representations of these expansions reveal their Stieltjes behavior for q ⩾ 1 and Padé summability for q = 1, 2.     

Large angle production of stable particles heavier than the proton and a search for quarks at the CERN intersecting storage rings

Measurements have been performed on production of particles with mass 1.5 GeV/c² and charge $\text{?}\text{2}\text{3}$ for θ_lab = 62.5° and $\text{s}\text{= 53}\text{GeV}$. At p_T = 0.7 GeV/c the relative rate of production of antideuterons to π^? is (5 ± 1) × 10^?5. The deuteron to antideuteron ratio is 3.7 ± 1.2. No new stable particle has been amongst 0.7 × 10⁸ charged particles entering our detector.     

Growth Rates and Explosions in Sandpiles

We study the abelian sandpile growth model, where n particles are added at the origin on a stable background configuration in ? ^d . Any site with at least 2d particles then topples by sending one particle to each neighbor. We find that with constant background height h≤2d?2, the diameter of the set of sites that topple has order n ^1/d . This was previously known only for h<d. Our proof uses a strong form of the least action principle for sandpiles, and a novel method of background modification. We can extend this diameter bound to certain backgrounds in which an arbitrarily high fraction of sites have height 2d?1. On the other hand, we show that if the background height 2d?2 is augmented by 1 at an arbitrarily small fraction of sites chosen independently at random, then adding finitely many particles creates an explosion (a sandpile that never stabilizes).