Oriented elliptic Rydberg atoms have been formed in a thermal beam of Li atoms by the adiabatic crossed-field method. All coherent elliptic quantum states from linear to circular can be produced by this method. The orientation and eccentricity is controlled by the external fields. While the formation of circular states by the crossed-field method has already been established experimentally, the radiative decay of the Rydberg atoms formed here was measured and compared with theory to verify that highly eccentric elliptic quantum states may also be formed.

The radiative decay rate of ${\mathrm{C}}^{4+}$ ions in the metastable 1s2${\mathit{s}}^3$${\mathit{S}}_1$ state has been measured at the ion storage ring TSR in Heidelberg, observing the time dependence of the dielectronic recombination rate on resonances characteristic for this metastable state. The very accurate result of 48.57±0.11 ${\mathit{s}}^{\mathrm{-}1}$ allows us to distinguish between different theoretical approaches. Our result is in excellent agreement with a calculation of the magnetic-dipole decay rate using nonrelativistic radial wave functions for the heliumlike carbon ion.

Double ionization of helium by single-photon impact is analyzed for photon energies from 4 to 12 keV. Many-body perturbation theory is applied to obtain the Compton scattering contribution to the total cross section for double ionization. Compton scattering dominates photoionization above 6 keV. Despite the differences between the two processes, the ratio of double to single ionization by Compton scattering appears to approach the asymptotic value given by photoionization calculations. These ratios are in agreement with recent experiments.

We develop a multichannel quantum defect formulation to describe the collision of a Rydberg or continuum electron with a vibrating and rotating polyatomic ion. We formulate a full rovibronic frame transformation which accounts simultaneously for vibrationally and rotationally inelastic collisions (preionization) and l uncoupling. Interactions among degenerate Rydberg series, arising from Jahn-Teller distortions of molecular geometry, play an important role in the formulation. An application to the ${1\mathrm{s}}^2$${3\mathrm{s}\mathrm{A}}_1^{\prime }$→${1\mathrm{s}}^2$ε${\mathrm{pA}}_2^{\mathrm{″}}$,εpE′ Rydberg photoabsorption spectrum of ${\mathrm{H}}_3$ accounts for many of its observed features.

We report results of one electron capture by highly charged ions colliding with laser excited aligned ${\mathrm{Na}}^{\mathrm{*}}$(3p). The O vi(10→8) photon emission cross section after electron capture by the ${\mathrm{O}}^{6+}$ projectile is measured in the collision energy range 2-8 keV/amu. Effects of the ${\mathrm{Na}}^{\mathrm{*}}$(3p) orbital alignment on the ) O vi(10→8) emission are observed and found to be ‘‘reversed’’ as compared to the ${\mathrm{He}}^{2+}$→${\mathrm{Na}}^{\mathrm{*}}$(3p) collision system. Classical trajectory Monte Carlo calculations agree with the measured data and indicate that capture to states with n>10, contributing to the O vi(10→8) emission via cascades, plays a crucial role in the alignment cross sections.

The singlet decay rate has been measured using magnetic singlet-triplet state mixing for positronium formed in a ${\mathit{N}}_2$-isobutane gas mixture. We find ${\lambda }_{\mathit{s}}$=7990.9±1.7 μ${\mathrm{s}}^{\mathrm{-}1}$. At 215 ppm this result is 6.5 times more accurate than the previous measurement [D. W. Gidley, A. Rich, E. Sweetman, and D. West], and is the first measurement sensitive enough to test the relative order ${\mathrm{\alpha }}^2$lnα term in the singlet decay rate calculation.

Energetics and dynamics of Coulombic fission of small doubly charged potassium clusters subsequent to the ionization of singly charged ones are investigated experimentally and theoretically. Fission is shown to occur predominantly via ${\mathrm{K}}_{\mathit{n}}^{++}$→${\mathrm{K}}_{\mathit{n}\mathrm{-}3}^{+}$+${\mathrm{K}}_3^{+}$ for 5≤n≤12. The close correspondence between the measured and the calculated kinetic energy release accompanying the fission process allows a deeper understanding of the dynamics and energy redistribution mechanisms in fission of metallic clusters.

We demonstrate that some chaotic parameter subsets of a class of spatiotemporal chaotic systems modeled by globally coupled maps are riddled. That is, for every point in the chaotic parameter subset, there are parameter values arbitrarily nearby that lead to nonchaotic attractors. A consequence is an extremely sensitive parameter dependence characterized by a significant probability of error in numerical computation of asymptotic attractors, regardless of the precision with which parameters are specified.

Coherent behavior in ensembles of globally coupled maps is investigated in the limit of infinite number of elements. A self-consistent approach based on a nonlinear Frobenius-Perron equation is proposed for such systems, and a possibility of quasiperiodic and chaotic behavior of the mean field is demonstrated. For the study of finite ensembles a noisy nonlinear Frobenius-Perron equation is derived. Previous observations of violations of the law of large numbers are explained.

Synchronization of a pair of chaotic diode resonators has been experimentally achieved by applying a minute feedback signal to the amplitude of the drive voltage of a slave resonator. The signal is proportional to the voltage difference between the two resonators and is applied for a fraction of the driving cycle. This method is the synchronization analog of the occasional proportional feedback scheme developed by Hunt for controlling unstable periodic orbits in chaotic attractors.

Mean-field electrodynamics, including both α and β effects while accounting for the effects of small-scale magnetic fields, is derived for incompressible magnetohydrodynamics. The principal result is α=(${\mathrm{\alpha }}_0$+${\mathrm{\beta }}_0$R⋅∇×R)/(1+${\mathit{R}}^2$), β=${\mathrm{\beta }}_0$; where ${\mathrm{\alpha }}_0$,${\mathrm{\beta }}_0$ are conventional kinematic dynamo parameters, the reduction factor is proportional to the mean magnetic field R=${\mathit{R}}_{\mathit{m}}^{1/2}$B/(ρ${\mathit{V}}^2$${)}^{1/2}$, ${\mathit{R}}_{\mathit{m}}$ is the magnetic Reynolds number, and V is the characteristic turbulent velocity. This result follows from a generalization of the Zeldovich theorem to three dimensions, exploiting magnetic helicity balance.

When the scaled growth rate of a free-electron laser (FEL) is plotted as a function of the scaled thermal velocity for the case of ideal beam compression, we find two distinct cases. If the FEL is in the energy-spread-dominated regime, the growth rate can be improved as a result of compression provided the scaled thermal velocity is less than unity. Surprisingly, we find that the growth rate is always improved if the FEL is in the emittance-dominated regime.

A low-frequency whistler wave packet is excited with a pulsed magnetic loop antenna in a large laboratory plasma (1 m diam×2.5 m, ${\mathit{n}}_{\mathit{e}}$=7×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}3}$, ${\mathrm{kT}}_{\mathrm{e}}$=1.3 eV, ${\mathit{B}}_0$=20 G). Multipoint (${10}^4$) measurements of the wave magnetic field, B(r,t), and 4D fast Fourier transformation, B(k,ω), both verify the dispersion of oblique plane whistler modes and permit the calculation of the wave electric field, decomposed into its rotational (inductive) and irrotational (space charge) contributions, E(r,t)=${\mathbf{E}}_{\mathrm{ind}}$+${\mathbf{E}}_{\mathrm{sc}}$. The space charge density, ρ(r,t), for a whistler wave is also shown.

Field ion microscope observations show that individual Rh adatoms on the Rh (100) surface are trapped in the four lattice sites adjacent to an Ir substitutional atom intentionally embedded into the surface. The activation barrier for the Rh adatom to escape from the impurity trap is 0.95 eV, considerably higher than the self-diffusion barrier on the defect-free surface (0.83 eV). The activation barrier to move between the four equivalent trap sites is 0.76 eV. The increased binding along with a higher Rh desorption field at the trap sites imply a stronger Ir-Rh bond compared to Rh-Rh.

The velocity time correlation function of a hard sphere fluid has been calculated using a generalized Langevin formulation of kinetic theory. When the memory function is approximated by its zero time value, the Langevin equation describes an overdamped harmonic oscillator in which the damping term arises from Enskog (uncorrelated collision) friction and the oscillator frequency arises from three body correlated collision sequences. For very high density fluids, the velocity time correlation function is in good agreement with molecular dynamics simulations on hard sphere fluids and the vibrational frequency is in close proximity to the Debye frequency of argon.

Using Monte Carlo computer simulations, we find strong evidence for a novel, finite-temperature, Ising-like transition in the alignment of unit cells in icosahedral quasicrystals. The Ising-like transition may be related to the transition in phason behavior from a locked (Penrose-tiling-like) phase at low temperatures to an unlocked (random-tiling-like) phase at high temperatures.

Diffraction approaches suggest that some quasicrystal structures can be described as hierarchical packing of atomic clusters. When treated as spherical potentials, these clusters may contain ‘‘magic numbers’’ of electrons which allow exact filling of the electronic shells of the hierarchy of wells. Physical propeties such as high resistivity and diamagnetism are consistent with the model. Formation of quasicrystals at very critical composition is also explained.

We study a mesoscopic kinetic model for step flow on crystal surfaces in the presence of impurities. The evolution of the system of steps in the small line tension limit leads to the formation of complex highly connected step patterns. We identify repeating features in the patterns and calculate them analytically by analyzing a simplified mean-field-like model. For the same model we also calculate analytically the coarsening with time of the typical length scale associated with the patterns. All the analytical results are in excellent quantitative agreement with numerical simulations.

The surface damange induced on Pt(111) by single rare gas ion impacts with energies down to a few hundred eV has been investigated by scanning tunneling microscopy. In addition to craters and adatom islands there are also characteristic reconstruction patterns in the vicinity of the ion impacts. It is demonstrated that these reconstructed areas are nuclei of the reconstruction network which has been discovered recently to be induced by Pt vapor phase deposition. The formation of these nuclei by ion bombardment is discussed in terms of currently used damage generation models.

Using the variational density-functional perturbation theory, we compute the phonon band structure, the interatomic force constants, the dielectric tensor, and the Born effective charge tensors of stishovite, a crystalline form of ${\mathrm{SiO}}_2$ with sixfold coordinated silicon atoms. Comparsion with available experimental data shows agreement at the level of a few percent. Access to the real-space interatomic force constants allows us to analyze the interplay between long-range ionic interaction and short-range covalent bonding, as well as criticize available two-body interatomic potentials.