Theoretical cross sections for resonant transfer and excitation followed by a stabilizing radiative transition are compared with experimental data for ${\mathrm{F}}^{6+}$+${\mathrm{H}}_2$, ${\mathrm{Ca}}^{17+}$+${\mathrm{H}}_2$, and ${\mathrm{Ca}}^{17+}$+He collisions. Extensive calculations of radiative and nonradiative rates were performed with the Hartree-Fock atomic model for Be-like fluorine and calcium. The energy dependence and the main features of the experimental data are explained well by our calculations in the impulse approximation. The calculated and experimental absolute cross sections are also in agreement within the quoted experimental uncertainties.

The strong-potential Born approximation is analyzed in a channel-distorted-wave approach. Channel-distorted SPB wave functions are reduced to a conventional form in which the standard off-energy-shell factor g has been replaced by a modified factor γ, which represents a suitable average of g over the momentum distribution of the distorted-channel function. The modified factor is evaluated in a physically realistic model for the distortion potential, and it is found that γ is well represented by a slowly varying phase factor. The channel-distorted SPB approximation is accordingly identical to the impulse approximation if the phase variation of γ can be ignored. This is generally the case in applications to radiative electron capture and to a good approximation for ordinary capture at not too small velocities.

We have observed nonresonant multiphoton electron detachment of ${\mathrm{H}}^{\mathrm{-}}$ ions in moderately intense (a few tens of GW/${\mathrm{cm}}^2$) laser fields. A well-collimated beam of ${\mathrm{H}}^{\mathrm{-}}$ ions with an energy of 581 MeV was intersected by focused 10.6-μm radiation from a pulsed ${\mathrm{CO}}_2$ laser. The center-of-mass photon energy was tuned using the relativistic Doppler shift so that the minimum number of simultaneous photons required for electron detachment ranged from three to sixteen. Definite signals were observed for the minimum photon number ranging from three to eight. Our preliminary results show evidence for structure in the relative total cross section.

A scheme for a precision measurement of the 1S-2S transition frequency in positronium and muonium is reported, and corrections to the two most recent experiments are presented which bring their results into agreement with theory.

Chromium is the only member of the transition-group elements with a well developed Rydberg structure appearing in its 3p-absorption spectrum. New high-resolution measurements of Mn, ${\mathrm{Mn}}^{+}$, and Cr have revealed weak Rydberg structure in ${\mathrm{Mn}}^{+}$ and an analysis of the data shows that the anomalous Cr 3p absorption spectra is due to a unique relationship between its energy levels, and not to the previously supposed fact that Cr has an unpaired 4s electron.

Although π phase shifts in an input Stokes beam are known to initiate soliton formation in a Raman amplifier, the observed shot-to-shot amplitude fluctuations have gone unexplained. It has been suggested that recently observed frequency shifts caused by quantum fluctuations may be related to the observed soliton decay. We show that frqequency shifts of the magnitude observed from these quantum fluctuations lead to soliton decay, and thus, are indeed the probable cause of observed soliton decay.

Berry’s phase in the coherent excitation of a two-level atom is shown to be an observable effect, as a shift of the side bands of the Mollow’s triplet. Berry’s phase effects, the adiabatic following model, and nonadiabatic evolution of a two-level atom are discussed in a unified manner.

The crumpling transition of D-dimensional elastic membranes is studied for large dimensions of embedding space d. The magnetic and thermal critical exponents $y_m$ and $y_t$ for isotropic membranes are obtained in a 1/d expansion. Both exponents vanish simultaneously at a lower critical dimension $D_{\mathrm{LC}=2\mathrm{}\mathrm{-}2/\mathrm{d}+\mathrm{O}(1/d^2}$). We also consider the role of self-avoidance and of elastic anisotropies.

This paper presents a detailed characterization of the plasma conditions near the critical density of a laser-produced plasma. Solid spherical plastic targets with small aluminum tracer dots buried below overcoated plastic layers have been uniformly illuminated with green laser light at irradiances of ${10}^{14}$–${10}^{15}$ W/${\mathrm{cm}}^{\mathrm{-}2}$. Time-resolved temperature and density profiles were obtained by using x-ray emission spectroscopy. Detailed comparisons with hydrodynamic simulations show that the thermal transport is well characterized by a flux limit of 0.1.

A stationary distribution for Langevin equations driven by colored noise is obtained, in the weak-noise limit, from the configuration-space Lagrangian-like function. The derivation makes no explicit use of Markovian, Fokker-Planck, or small-correlation-time approximations. Markovian approximations based on the Lagrangian, which do not involve truncated expansions, are also discussed.

The negative muonium ion, ${\mathrm{Mu}}^{\mathrm{-}}$≡${\mathrm{\mu }}^{+}$${\mathrm{e}}^{\mathrm{-}}$${\mathrm{e}}^{\mathrm{-}}$, has been produced by double electron pickup as a beam of positive muons passes through thin foils of various materials. The ${\mathrm{Mu}}^{\mathrm{-}}$ ions were detected by electrostatically accelerating and analyzing the ions in a magnetic time-of-flight spectrometer. Yields of ${\mathrm{Mu}}^{\mathrm{-}}$, Mu and ${\mu }^{+}$ as well are reported when ${\mu }^{+}$ with kinetic energies from 380 to 800 keV impinge on thin Be, Al, and Au foils. A Monte Carlo simulation provides good agreement with the experimental results.

An improved version of the Padé method is employed to extract reasonable information about the expected power-law behavior of observables, represented formally by divergent power-series expansions in some coupling parameter z, in the z→∞ limit. Case studies of interest include the anharmonic vibrator, the hydrogenic Stark-like, and the Zeeman systems.

We present a combined application of perturbation and configuration-interaction calculation for the nonrelativistic electrostatic energy for the He 1s4f ${}_{}{}^1{}_{}{}^{}$,3F multiplets with particular emphasis given to the contributions beyond the second order from perturbation calculation. The numerical efficiency and the quantitative accuracy of our ab initio calculation are greatly improved with the use of a finite basis set constructed from the B splines. The calculated fine-structure level splittings for the 1s4f ${}_{}{}^1{}_{}{}^{}$,3F multiplets compare very well with the result from the most recent rf electric-resonance experiment.

An alternative theory for charge exchange at arbitrary energies is introduced. The method is a Schwinger-type variational unification of the leading second-order Born perturbation approximations and the efficient $L^2$-expansion theories. This new variational principle is devised in accordance with the correct boundary conditions for three charged particles. The present theory exhibits a number of advantages over all the existing methods in regard to both the conceptual and computational points of view.

The rate constants of the energy-pooling collisions in the Na-Rb and K-Rb vapor mixtures, resonantly excited by two cw dye lasers, have been measured relative to a known energy-pooling rate constant of a homonuclear reaction. To isolate the heteronuclear contribution in the fluorescence spectrum, a double-modulation technique has been adopted. The effective lifetimes of the excited levels that explicitly appear in the solution equation have been directly measured by using pulsed lasers. A discussion about the collision cross-section dependence on the energy defect involved in the energy-pooling collisions is reported.

${\mathrm{Li}}^{+}$+${\mathrm{D}}_2$ collisions are investigated in an energy range from 0.600 to 3.0 keV and for τ (the reduced scattering angle equal to Eθ) values out to 2.5 keV deg. The electronically elastic channel is found to be dominant and is studied in detail as a continued test of a scaling law which predicts that a reduced energy loss f should depend only on τ. Earlier results that scaled were particularly useful since they could test the validity of a calculated potential-energy surface. Although we clearly find the scaling to break down at small scattering angles, a related theoretical study shows that the calculated surface may still be tested by the experimentally determined f(τ). Electronically inelastic processes resulting from singly as well as doubly excited states of the ${\mathrm{D}}_2$ are also found. The two inelastic processes occur with comparable probabilities which rise to about 0.2 at the largest τ values.

Recent measurements of vibrorotational excitation in low-keV-energy ${\mathrm{Li}}^{+}$+${\mathrm{D}}_2$ collisions have shown a breakdown in a rather general scaling law for projectile energy loss in the quasielastic channel. This scaling law maintains that in small-angle impulsive scattering determined by a conservative potential, classical trajectory calculations of atomic projectiles on diatomic targets predict a universal scaled vibrorotational excitation energy spectrum when Q/E${\theta }^2$ is plotted as a function of τ=Eθ. The breakdown in scaling is here shown to be caused by quantization of vibrational energy in the target molecule. It is also shown that the critical angle at which departure from purely elastic scattering occurs is given by E${\theta }_c^2$=const. The theory predicts that in the collision-energy regime of 500 eV to a few keV and for scattering angles in excess of a few tenths of a degree, the vibrorotational excitation energy in ${\mathrm{D}}_2$ is almost entirely vibrational, with only a small fraction of the excitation energy going into rotational degrees of freedom.

We have calculated dielectronic recombination cross sections and rate coefficients for the Ne-like ions ${\mathrm{P}}^{5+}$ and ${\mathrm{Cl}}^{7+}$ in configuration-average, LS-coupling, and intermediate-coupling approximations. Autoionization into excited states reduces the cross sections and rate coefficients by substantial amounts in all three methods. There is only rough agreement between the configuration-average cross-section results and the corresponding intermediate-coupling results. There is good agreement, however, between the LS-coupling cross-section results and the corresponding intermediate-coupling results. The LS-coupling and intermediate-coupling rate coefficients agree to better than 5%, while the configuration-average rate coefficients are about 30% higher than the other two coupling methods. External electric field effects, as calculated in the configuration-average approximation, are found to be relatively small for the cross sections and completely negligible for the rate coefficients. Finally, the general formula of Burgess was found to overestimate the rate coefficients by roughly a factor of 5, mainly due to the neglect of autoionization into excited states.

We report on measurements of the nuclear-spin diffusion coefficient in gaseous helium below 1 K. Both $D_{33}$ (self-diffusion in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$) and $D_{34}$ (diffusion of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$) are obtained from $T_2$ measurements in applied magnetic gradients. We operate at low densities, where transport properties are governed by two-body collisions. Predictions from various helium-helium potentials have been computed and are compared with the experimental results. A rough agreement is obtained, although theoretical values for $D_{33}$ seem somewhat too small. Relative variations with temperature are well described by theory between 4.2 and 0.5 K (within 10%).

The influence of a laser field on the dynamics of fast (e,2e) collisions in atomic hydrogen is analyzed in the asymmetric, coplanar geometry. Particular attention is devoted to the construction of the dressed (laser-modified) target wave functions, in both the initial and final states. A detailed account is also given of the techniques we have used to evaluate the scattering amplitudes. In addition to a nonperturbative approach (valid to all orders in the laser-projectile interaction), we also discuss a second-order treatment in the combined electron-atom and laser-system (electron plus atom) interactions. The influence of the laser parameters (frequency, intensity, and direction of polarization) on the angular distribution of the ejected electron is discussed, and a number of illustrative examples are given. The structure of the triple differential cross section in the vicinity of resonances is also analyzed.