A crossed-beam technique incorporating time-of-flight analysis and coincidence counting of the collision products has been used to study ${\mathrm{Pb}}^{q+}$ formation with q up to 8 in collisions between ground-state Pb atoms and ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{2+}$ ions within the range 50–600 keV ${\mathrm{amu}}^{\mathrm{-}1}$. The separate cross sections for simple charge transfer, transfer ionization, and pure ionization leading to the formation of ${\mathrm{Pb}}^{q+}$ ions have been obtained and the relative importance of these processes has been established. Accurate measurements and rigorous theoretical descriptions of these multielectron processes in such heavy atoms are difficult and data are still very limited. The present measurements have been designed to extend our previous studies of multiple ionization of a few selected heavy metal atoms and to provide a further check on the extent to which the main collision processes can be described quantitatively in terms of simple models based on an independent electron description. In our previous work with Fe, Cu, and Ga atoms using the same experimental approach, we were able to describe the formation of multiply charged ions through both transfer ionization and pure ionization with a high degree of success using an independent electron model. However, the present results for Pb show that the success of this simple approach is much more limited for these much heavier atoms.

We have used the convergent close-coupling method and a unitarized first-order many-body theory to calculate integral cross sections for elastic scattering and momentum transfer, for excitation of the ${5d}^2{}^{1}S,$ $6s6p{}^1{P}_1,$ $6s7p{}^1{P}_1,$ $6s8p{}^1{P}_1,$ $6s5d{}^1{D}_2,$ ${5d}^2{}^1{D}_2,$ $6s6d{}^1{D}_2,$ $6p5d{}^1{F}_3,$ $6s4f{}^1{F}_3,$ $6p5d{}^1{D}_2,$ $6s6p{}^3{P}_{0,1,2},$ $6s5d{}^3{D}_{1,2,3},$ and $6p5d{}^3{D}_2$ states, for ionization and for total scattering by electron impact on the ground state of barium at incident electron energies from 1 to 1000 eV. These results and all available experimental data have been combined to produce a recommended set of integral cross sections.

The collision, scattering, and absorption differential cross sections for two-photon Compton scattering in both the forward and backward hemispheres have been measured as a function of independent final photon energy for 0.662 MeV incident γ photons as produced by an 8-Ci ${}^{137}\mathrm{Cs}$ radioactive source. The two simultaneously emitted photons in this process are detected in coincidence using two NaI(Tl) scintillation spectrometers and 30 nsec timing electronics. Many systematic effects contributing to true events have been taken into account. The differential cross-section values agree with the theory within experimental estimated error.

The velocity basis of the Poincaré group is used in the direct product space of two irreducible unitary representations of the Poincaré group. The velocity basis with total angular momentum j will be used for the definition of relativistic Gamow vectors.

Double- through quintuple-electron capture processes in the 70-keV ${}^{15}{\mathrm{N}}^{7+}+\mathrm{Ar}$ collision system have been investigated by means of time-of-flight triple-coincidence measurements of Auger electrons, scattered projectile, and target recoil ions. Subpartial Auger-electron spectra corresponding to specific pairs of final projectile and recoil-ion charge states have been obtained and discussed within the framework of the extended classical overbarrier model [A. Niehaus, J. Phys. B 19, 2925 (1986)]. By allowing for target excitation, the model accounts reasonably well for the observed initial populations. Possible relaxation pathways of the populated multiply excited configurations have been identified. Measurements of this type allow a deeper understanding of the production and relaxation pathways of these configurations.

Experimental and theoretical cross sections for the excitation of ground-state lithium by ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{2+}$ impact are presented for the 2–30 keV/amu energy regime. $\mathrm{Li}\mathrm{}\left(2s\right)\mathrm{}$ excitation up to the $\mathrm{Li}\mathrm{}(n=4\mathrm{})\mathrm{}$ level was simulated by means of the atomic-orbital close-coupling method. Experimentally, absolute emission cross sections were determined by observing the $\mathrm{LiI}(nd-2p,n=3–6)$ and $\mathrm{LiI}(ns-2p,n=4–6)$ line radiation after ion impact. Furthermore, a few measurements have been performed on high-$n$ excitation $\left[\mathrm{Li}\right(2\mathrm{}\overrightarrow{s}nd,n=7\mathrm{}–9\left)\right]$ by ${\mathrm{He}}^{2+}$ impact.

A quantum-mechanical close-coupled calculation for collisions of spin-polarized triplet helium atoms in a magnetostatic trap is presented in which the Penning and associative ionization processes are represented by a complex optical potential. The rate coefficients for the spin relaxation and relaxation-induced Penning ionization processes for a range of magnetic fields and temperatures, spanning the cold and ultracold temperature regimes, have been calculated and the sensitivity of these results to uncertainties in the molecular potentials and autoionization width investigated. The rate constants for both elastic and inelastic processes were found to be particularly sensitive to the short-range ${}^5{\Sigma }_g^{+}$ molecular potential and, to a lesser extent, the rate constants for relaxation-induced Penning ionization displayed sensitivity to the short-range form of the ${}^1{\Sigma }_g^{+}$ molecular potential and the autoionization width.

A comprehensive eigenchannel R-matrix study of photodetachment of ${\mathrm{He}}^{-}\hspace{0.5em}\left(1s2s2p{}^4{P}^o\right)$ is presented for the energy region of the $\mathrm{He}\hspace{0.5em}\left(1\mathrm{snl}{}^{3}l\right)$ thresholds, where $3<~n<~5.$ Over this energy region we present all partial cross sections which have been measured experimentally, including theoretical predictions for the $\mathrm{He}\hspace{0.5em}\left(1s3p{}^{3}P\right)$ partial cross section, as well as energies and widths for all resonances, and identifications of all major ones. Near the $\mathrm{He}\hspace{0.5em}\mathrm{}(n=3\mathrm{})\mathrm{}$ thresholds, we predict two ${}^4{D}^e$ resonances that to our knowledge have previously been neither predicted nor observed, and present results showing their effects on partial cross sections and photoelectron angular distributions; our $\mathrm{He}\left(1s2s{\hspace{0.5em}}^{3}S\right)$ and $\mathrm{He}\left(1s2p{\hspace{0.5em}}^{3}P\right)$ partial cross-section results are shown to be in excellent agreement with relative measurements of Klinkmüller and co-workers [Phys. Rev. A 56, 2788 (1997); J. Phys. B 31, 2549 (1998)]; our predicted partial cross sections and resonance energies and widths are also compared with other theoretical predictions. Near the He $(n=4\mathrm{}$ and 5) thresholds, we predict about 30 quartet Feshbach resonances and four quartet shape resonances which have not been observed or predicted before; our predicted $\mathrm{He}\hspace{0.5em}\left(1s3p{}^{3}P\right)$ partial cross section is in excellent agreement with measurements of Kiyan et al. [Phys. Rev. Lett. 81, 2874 (1998)], and we present identifications for all but one of the experimentally observed resonance features; our resonance energies and widths are also compared with other theoretically predicted results. Because resonances in the energy region considered have in general only small effects on the total photodetachment cross section, we show that alternative partial cross sections for $\mathrm{He}\left(1\mathrm{snl}{}^{3}l\right)$ states tend to mirror each other in the vicinity of a resonance, as predicted analytically recently by us [Phys. Rev. A 59, R1731 (1999)]. An exceptional case is found, however, for several ${}^4{P}^e$ window resonances in the vicinity of the $\mathrm{He}\mathrm{}(n=4\mathrm{})\mathrm{}$ thresholds: the partial cross sections in the vicinity of these three resonances mimic each other. We prove analytically in an appendix that such mimicking behavior occurs whenever the Fano-Cooper profile parameter ${\rho }^2$ [Phys. Rev. A 137, A1364 (1965)] tends to unity.

Partial cross sections for Ar ${K-L}_2{L}_3{(}^1{D}_2)np,$ $n=4\mathrm{}$ and 5 spectator Auger states excited by x-ray absorption across the K edge, were measured and compared with calculations based on the theory of radiationless resonant Raman scattering. Core relaxation and coherence among bound and continuum intermediate states produce shake-up, shake-down, and photoelectron-recapture effects in the cross sections. The width and position of the $4p$ spectator Auger peak are shown to be sensitive to resonance structure in the partial cross section via averaging over the x-ray bandwidth.

The lowest ${}^1{S}^e$ resonance state in a family of symmetric three-body Coulomb systems is systematically studied as a function of the mass-ratio M for the constituting particles. The Siegert pseudostate method for calculating resonances is described and accurate results obtained by this method for the resonance position $\mathcal{E}\mathrm{}\left(M\right)\mathrm{}$ and width $\Gamma \mathrm{}\left(M\right)\mathrm{}$ in the interval $0<~M<~30$ are reported. The principal finding of these calculations is that the function $\Gamma \mathrm{}\left(M\right)\mathrm{}$ oscillates, almost vanishing for certain values of M, which indicates the existence of an interference mechanism in the resonance decay dynamics. To clarify this mechanism, a simplified model obtained from the three-body Coulomb problem in the limit $\overrightarrow{M}\infty$ is analyzed. This analysis extends the range of M up to $M=300\mathrm{}$ and confirms that $\Gamma \mathrm{}\left(M\right)\mathrm{}$ continues to oscillate with an increasing period and decreasing envelope as M grows. Simultaneously it points to semiclassical theory as an appropriate framework for explaining the oscillations. On the basis of Demkov’s construction, the oscillations are interpreted as a result of interference between two paths of the resonance decay on the Riemann surface of adiabatic potential energy, i.e., as a manifestation of the Stueckelberg phase. It is shown that the implications of this interpretation for the period and envelope of the oscillations of $\Gamma \mathrm{}\left(M\right)\mathrm{}$ agree excellently with the calculated results.

The light-induced desorption and diffusion of alkali-metal atoms in organic films are interesting fields of investigation. An impressive demonstration is given by the recently observed light-induced atomic desorption (LIAD) effect, where a huge alkali-metal atom desorption from siloxane films, previously exposed to atomic vapors, is induced by weak and nonresonant light. In this paper, experimental data and a one-dimensional theoretical model of the effect are presented. The model gives a good description of the vapor density dynamics by taking into account both the atomic diffusion inside the coating and the surface desorption. General equations are reported and discussed within the limits of experimental interest. The potential barrier at the vapor-surface interface and the activation energy for Rb in (poly)dimethylsiloxane have been determined.

We have evaluated electron capture and excitation cross sections for ${\mathrm{H}}^{+}+{\mathrm{Na}}_n$ collisions $\mathrm{}(n=8,20,40,92\mathrm{})\mathrm{}$ in the impact energy range 40–500 eV. The theoretical method includes the many-electron aspect of the problem and makes use of realistic cluster potentials obtained with density-functional theory and a spherical jellium model. Both electron capture and excitation cross sections increase monotonically with cluster size, but the rate of this increase is much more pronounced than expected from purely geometrical considerations. Also, capture cross sections are between one and two orders of magnitude larger than the geometrical cross sections. For the larger systems, our results differ from recent theoretical estimates obtained at higher impact energies.

We have systematically studied emission patterns of fragments arising from the Coulomb explosion of ${\mathrm{N}}_2,$ ${\mathrm{Cl}}_2,$ and ${\mathrm{I}}_2$ molecules when exposed to intense, linearly polarized laser fields. The experiments are performed at 395, 610, and 790 nm, using two different pulse durations (130 fs and 2 ps) and choosing two different peak intensities ${(10\mathrm{}}^{15}$ and $2\times {10}^{16}{\mathrm{W}\mathrm{}\mathrm{cm}}^{\mathrm{-}2}).\mathrm{}$ We show that the anisotropy of the emission patterns increases with the number of absorbed photons necessary to produce the parent molecular ion. The set of experimental results suggest that the alignment process occurs in the leading edge of the laser pulse at moderate intensities $(<\mathrm{}{10}^{14}{\mathrm{W}\mathrm{}\mathrm{cm}}^{\mathrm{-}2})$ where the multiphoton regime prevails. We explain these observations in terms of the rotational pumping model, as demonstrated by statistical simulations of multiphoton absorption and emission. The present study confirms that, in most cases, the confined emission of fragments along the laser electric field is due to the alignment of the transient molecular ions.

We suggest a method of binding atoms to ferromagnetic wire through the interaction between the atomic magnetic moment and the magnetic field of the wire. It is shown that the two-dimensional $1/{\rho }^2$ potential arises between the atom and the wire with magnetization perpendicular to the latter, the three-dimensional ${1/r}^2$ potential arises between the atom and the end of the wire with magnetization parallel to the wire, the two-dimensional $1/\rho$ potential arises when magnetization of the wire is parallel to the wire, and the magnitude of magnetization changes linearly along the wire. We also discuss the possibility of experimental realization of binding of sodium atoms to the ferromagnetic iron wire.

We study the dynamics of the potassium atom in the midinfrared (12-, 13-, and 14-photon ionization), high-intensity, short laser pulse regime. We ascertain numerical convergence by comparing the results obtained by the direct expansion of the time-dependent Schrödinger equation onto B splines to those obtained by the eigenbasis expansion method. We present ionization curves in the 12-, 13-, and 14-photon ionization range for potassium. The ionization curve of a scaled system, namely hydrogen starting from the $2s,$ is compared to the 12-photon results. In the 13-photon regime, a dynamic resonance is found and analyzed in some detail. The results for all wavelengths and intensities, including hydrogen, display a clear plateau in the peak heights of the low-energy part of the above threshold ionization spectrum, which scales with the ponderomotive energy $U_p$ and extends to $(2.8\mathrm{}\pm {0.5)U}_p.$

We report on the hyperfine-structure measurements of the ${5P}_{1/2}$ and ${5P}_{3/2}$ states as well as the isotope shift of the $D_1$ transition of radioactive ${}^{82}\mathrm{Rb}\hspace{0.5em}{(t}_{1/2}=75\mathrm{}\hspace{0.5em}\mathrm{s})$ atoms trapped in a magneto-optical trap. The systematic effects of light shift (ac Stark shift) and power broadening were explored to verify the accuracy of our trap and probe method against saturation spectroscopy results in ${}^{85}\mathrm{Rb}.$ The hyperfine-splitting magnetic-dipole coefficient (A) for the ${}^{82}\mathrm{Rb}\hspace{0.5em}{5P}_{1/2}$ state and the isotope shift of the $D_1$ transition $\left(\delta {\nu }^{82-85}\right)$ was measured to be $122.7\left(1.0\right)\mathrm{}\hspace{0.5em}\mathrm{MHz}$ and $-150.8\left(2.0\right)\mathrm{}\hspace{0.5em}\mathrm{MHz},$ respectively. The hyperfine splitting for the ${}^{82}\mathrm{Rb}\hspace{0.5em}{5P}_{3/2}$ state was determined to be 90.3(1.5) MHz in agreement with the previous measurement of 89.3(9.0) MHz [C. Thibault et al., Phys. Rev. C 23, 2720 (1981)]. These measurements provide key information that is needed to manipulate and determine the polarization of trapped ${}^{82}\mathrm{Rb}$ atoms for a parity violating $\beta$-asymmetry measurement.

We calculate the effects of two-body interactions on the low-frequency oscillations of a normal Fermi gas confined in a harmonic trap. The mean-field contribution to the collective frequencies is evaluated in the collisionless regime using a sum-rule approach. We also discuss the transition between the collisionless and hydrodynamic regimes with special emphasis on the spin dipole mode in which two atomic clouds occupying different spin states oscillate in the opposite phase. The spin dipole mode is predicted to be overdamped in the hydrodynamic regime. The relaxation time is calculated as a function of temperature and the effects of Fermi statistics are explicitly pointed out.

We have derived ab initioanalytical results for the shape of the double-structure potential well for a (3+5)-level atoms in the magneto-optical trap (MOT). We show that for a case of a (3+5)-level atom and a one-dimensional ${\sigma }^{+}-{\sigma }^{-}$ laser field, the sharp bottom part of the MOT potential well results from the two-photon processes between the atomic ground-state magnetic sublevels. These nonlinear processes are, in particular, responsible for atomic temperatures below the Doppler limit which is due to the one-photon processes in the MOT. We also find that in more complicated atomic schemes, even-order multiphoton processes contribute to the sharp and narrow MOT potential well.

The system of a three-level atom coupled to two quantized field modes with arbitrary detuning and density-dependent multiphoton interaction is studied by a dynamical algebraic method. We find an alternative su(3) dynamical algebraic structure within the system. Based on this su(3) structure, we diagonalize the Hamiltonian by making use of unitary transformations and obtain the eigenvalues, eigenstates, and time evolution operator for the system. The effective two-level Hamiltonian is also derived by unitary transformation. Finally the system governed by the Milburn equation is discussed and the exact solution of the Milburn equation presented.

One-photon detachment and two-photon nonresonant excess photon detachment of electrons from the ${\mathrm{H}}^{-}$ ion (outer-electron binding energy = 0.7542 eV) are observed with 1.165 eV laser pulses from a Nd:YAG laser (where YAG denotes yttrium aluminum garnet). A Penning ion source produces a pulsed 8 μA, 35 keV ${\mathrm{H}}^{-}$ beam that intersects a laser beam cylindrically focused down to a 17 μm full width at half maximum waist in the ion beam direction, creating a high-intensity interaction region with peak intensities of up to ${10}^{11}\hspace{0.5em}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2.$ The interaction time is 7 ps. The detached electrons are detected by a time-of-flight apparatus enabling us to detect a very small two-photon signal in the presence of a very large signal from single photon detachments. By rotating the linear polarization angle, we study the angular distribution of the electrons for both one- and two-photon detachments. The spectra are modeled to determine the asymmetry parameters and one- and two-photon cross sections. We find ${\beta }_2$ to be $2.54+0.44/-0.60$ and ${\beta }_4$ to be $2.29+0.07/-0.31,$ corresponding to a D state of $89+3/-12\%$ of the S wave and D wave detachments for the two-photon results. The relative phase angle between the S and D amplitudes is measured to be less than $59°.$ The measured cross sections are found to be consistent with theoretical predictions. The one-photon photodetachment cross section is measured to be $(3.6\mathrm{}\pm 1.7)\times {10}^{-17}\hspace{0.5em}{\mathrm{cm}}^2.$ The two-photon photodetachment generalized cross section is $(1.3\mathrm{}\pm 0.5)\times {10}^{-48}\hspace{0.5em}{\mathrm{cm}}^4\hspace{0.5em}\sec ,$ consistent with theoretical calculations of the cross section. The three-photon generalized cross section is less than $4.4\times {10}^{-79}\hspace{0.5em}{\mathrm{cm}}^6\hspace{0.5em}{\sec }^2.$