We measured the mobility of excess electrons in the strongly polar acetonitrile (${\mathrm{CH}}_3$ CN) gas at low densities as a function of density and temperature by the pulsed Townsend method. We found an unexpected strong density dependence of the 'zero-field' density-normalized mobility (μn) that cannot be explained only by different multiple-scattering effects. We propose a transport process where short-lived dipole-bound electron ground states as quasilocalized states are involved. Finally we discuss the experimentally observed anion mobilities as a function of density and temperature according to current theoretical approaches.

Total cross sections for transfer ionization in fast collisions of a bare nucleus with helium are examined in the four-body distorted-wave formalism. A special emphasis is given to a proper inclusion of dynamic electron-electron correlation effects. For this purpose, the four-body continuum distorted-wave (CDW-4B) approximation with the correct boundary conditions is introduced. Along with the appropriate potential operators containing a single electron placed on one and/or both nuclear centers, accompanied by the corresponding Coulomb waves for continuum intermediate states, the dielectronic interaction ${\mathrm{V}}_{12}$=1/${\mathrm{r}}_{12}$≡1/|r-${\to }_1$-r-${\to }_2$| also explicitly appears in the perturbation potential of the transition probability amplitude. The inclusion of the potential ${\mathrm{V}}_{12}$ is essential for the description of the Thomas P-e-e scattering, through which one of the target electrons could be captured or ionized without ever experiencing any direct interaction with the projectile P. The total cross sections ${\mathrm{\sigma }}_{\mathrm{if}}$ due to such a correlated CDW-4B theory are computed exactly and very efficiently by means of precise evaluation of certain seven-dimensional quadratures in momentum space. The proposed method is shown to be superior to the corresponding independent event model (CDW-IEM), which also proceeds through the same effort on multidimensional scattering integrals, but largely overestimates the measured values for ${\mathrm{\sigma }}_{\mathrm{if}}$ . Comparisons between the present results ${\mathrm{\sigma }}_{\mathrm{if}}$ and the available experimental data at E=30–600 keV/amu for transfer ionization in the ${\mathrm{He}}^{2+}$ -He collision yield satisfactory agreement at impact energies E⩾80 keV/amu. This is in full harmony with the well-known low-energy limit of the validity of the CDW-3B method assessed previously for the genuine three-body charge exchange in collisions between a fully stripped projectile and a hydrogenlike atomic target.

We calculate the cross sections for the production of one and more electron-positron pairs due to the strong electromagnetic fields in relativistic heavy-ion collisions. We derive the N-pair amplitude using the generating functional of fermions in an external field and the path-integral formalism. The N-pair production probability is found to be an approximate Poisson distribution. We calculate total cross sections for the production of one pair in lowest order, including corrections from the Poisson distribution up to third order. Furthermore, we calculate cross sections for the production of up to five pairs including corrections from the Poisson distribution.

In this paper we present numerical calculations for the process of bound-free electron-positron pair production following photon impact on bare nuclei. The calculations are based on exact Coulomb waves. We include total as well as differential cross sections for production of both K and L electrons for a wide range of photon energies and nuclear charge numbers. Significant deviations from lowest-order Born theory appear for moderate and high charge numbers in both the total cross section and, most dramatically, in the angular distributions of the emitted positrons. Our results for total K-shell cross sections for photon impact as well as for ion impact, in the latter case as estimated by the virtual photon method, basically confirm those of Aste et al. [Phys. Rev. A 50, 3980 (1994)]. However, we note that by inclusion of L-electron production, the cross section for the ion-induced process is increased by approximately 20% for heavy elements.

Calculations of cross sections and photoelectron angular distributions from the photodetachment of the 1s2s2p${\mathrm{}}^4$ P metastable state of ${\mathrm{He}}^{\mathrm{-}}$ have been performed from threshold to 100 eV using multiconfiguration Hartree-Fock wave functions for discrete states and coupling continuum channels with closed channels to include resonances. Ejection of each electron was considered and ejection plus excitation was included in connection with 1s photoabsorption. The ${1\mathrm{s}2\mathrm{p}}^2$ and ${2\mathrm{s}2\mathrm{p}}^2$ ${\mathrm{}}^4$ P resonances were found in good agreement with recent experiments and calculations; the reason that the former lies above the 2s threshold while the latter lies below the 1s threshold is discussed. The nonresonant 2p cross section is in excellent agreement with experiments and other calculations. The 2s results, in which Cooper minima are predicted, are not in agreement with a similar calculation, particularly for the Β parameter. The 1s cross section shows a large maximum just above threshold, much larger than the 1s cross section in neutral He, and at somewhat higher energy the cross section is dominated by 1s detachment plus excitation to the (2s3p±3s2p)${\mathrm{}}^3$ P and 3s3p${\mathrm{}}^3$ P autoionizing states of He.

The energy of the binary-encounter peak has been determined for 0.6 MeV/u O, F, Si, Ti, Cu, and Br ions colliding with ${\mathrm{H}}_2$ targets. The projectiles all had the same charge q=7, while the atomic number Z of the projectiles ranged from 8 (almost totally ionized) to 35 (retaining 28 electrons). We observe that the binary-encounter-peak energy for fixed q increases as Z increases. This trend is opposite to that observed when Z is fixed and the charge q is varied, and it demonstrates that the binary-encounter-peak energy depends not only on the net projectile charge but on the projectile core as well. The experimental trend is qualitatively reproduced by an impulse approximation showing that this variation in the binary-encounter-peak energy may be attributed to the effect that the projectile core potential has on the electron elastic-scattering cross section.

We prove quantum-classical correspondence for bound conservative classically chaotic Hamiltonian systems. In particular, quantum Liouville spectral projection operators and spectral densities, and hence classical dynamics, are shown to approach their classical analogs in the h→0 limit. Correspondence is shown to occur via the elimination of essential singularities. In addition, applications to matrix elements of observables in chaotic systems are discussed.

We present a quantitative study of the resonant structures of the overlapping 3pνd${\mathrm{}}^1$F and 3pνg${\mathrm{}}^1$F autoionization series in the photoionization from the bound excited ${}_{}{}^1{}_{}{}^{}\mathrm{D}$ states of Mg-like ${\mathrm{Al}}^{+}$ and ${\mathrm{Si}}^{2+}$ ions. The interference, both constructive and destructive, between the contributions from individual processes corresponding to transitions from specific initial to final-state configurations, are examined in detail. Our calculation shows that the photoionization from higher bound excited 3s${\nu }_{\mathrm{i}}$d${\mathrm{}}^1$D state is dominated by the shakeup of the outer d electron following the 3s→3p core electron excitation. For ${\mathrm{Al}}^{+}$ , our calculation reveals the presence of a narrow 3pνg${\mathrm{}}^1$F window resonance located on the higher-energy shoulder of its corresponding broad 3pνd${\mathrm{}}^1$F resonance. Unlike the usual isolated window resonance, which is dominated by the transition from the initial state to the continuum component of the final-state wave function, the 3s${\nu }_{\mathrm{i}}$d${\mathrm{}}^1$D→3pνg${\mathrm{}}^1$F window resonance results primarily from the energy variation of the bound component, i.e., the weighted νd radial function, of the final-state wave function in the vicinity of the 3pνg${\mathrm{}}^1$F resonance.

The charge-transfer rate coefficients for reactions of ${\mathrm{N}}^{2+}$(${2\mathrm{s}}^2$2p${\mathrm{}}^2$${\mathrm{P}}^{\mathrm{o}}$) with ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and CO are measured using ion storage. A cylindrical rf ion trap was used to store ${\mathrm{N}}^{2+}$ ions produced by laser ablation of a solid titanium nitride target. The rate coefficients were derived from the decay rate of the ion signal. The rate coefficients for the above three reactions are 3.38(0.35)×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ at ${\mathrm{T}}_{\mathrm{equiv}}$=2.9×${10}^3$ K, 2.10(0.18)×${10}^{\mathrm{-}9}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ at ${\mathrm{T}}_{\mathrm{equiv}}$=1.3×${10}^4$ K, and 3.37(0.29)×${10}^{\mathrm{-}9}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ at ${\mathrm{T}}_{\mathrm{equiv}}$=1.3×${10}^4$ K, respectively. No theoretical or other experimental values are available at this energy range.

In this paper, we report calculations of electron-hydrogen ionization whereby the final-state wave function is approximated by recently reported analytical three-body wave functions. In a first model we use the wave function of Alt and Mukhamedzhanov [Phys. Rev. A 47, 2004 (1993)], and in a second model we use the wave function of Berakdar [Phys. Rev. A 53, 2314 (1996)].

We present a microscopic description of the emission of fast electrons in glancing-angle ion-surface collisions. We employ a classical trajectory Monte Carlo approach that treats the primary production of kinetic electrons in close collisions and their subsequent transport through the surface region on the same footing. Dynamic image interactions and multiple scattering are explicitly included. As an application, we analyze the ejected electron spectra over a broad range of electron energies and emission angles for 0.2–0.5-MeV/u Li ions interacting with SnTe(001) surfaces. Good agreement is found with experiment for the shape of the spectrum of forward-ejected electrons containing prominent structures such as the convoy electron peak and the binary ridge.

Complex adiabatic potential curves are an essential input to atomic surface scattering calculations employing the coupled-states method. We present calculations for the ground state of hydrogen near a jellium surface with the density of aluminum. Two complementary techniques have been implemented: the complex rotation method and the stabilization method. We employ large-scale matrix diagonalization and realistic effective single-particle potentials. The influence of the surface potential on the adiabatic evolution of the wave function and the resonance parameters as a function of the distance d from the surface have been investigated. Application to the ground state H(1s) yields significant differences for the position and width of the resonance compared to previously available data. The applicability of semiclassical theory for resonance parameters is tested and the role of over-barrier transitions is highlighted.

The interaction of slow highly charged ions with many-electron targets leads to the formation of unstable, multiply excited projectiles. We simulated the formation of such hollow ions for slow incident ${\mathrm{Bi}}^{46+}$ projectiles and ${\mathrm{C}}_{60}$ targets. Our semiclassical overbarrier simulation includes resonant exchange and Auger emission of electrons. It models the dynamical variation of level occupations and charge states during the collision and predicts highly unstable hollow ions immediately after the collision. With respect to the subsequent downstream relaxation of the hollow ions, we propose a simple relaxation scheme that includes autoionizing and radiative transitions. As a consequence of this downstream relaxation, almost all of the resonantly captured electrons are emitted.

Single-particle states in the atomic trap employing the rotating magnetic field are found using the full time-dependent instantaneous trapping potential. These states are compared with those of the effective time-averaged potential. We show that the trapping is possible when the frequency of the rotations exceeds some threshold. Slightly above this threshold the weakly interacting gas of the trapped atoms acquires the properties of a quasi-one-dimensional system in the frame rotating together with the field. The role of the atom-atom interaction in changing the ideal gas solution is discussed. We show that in the limit of large numbers of particles the rotating field whose frequency is appropriately modulated can be utilized as a driving force principally for the center-of-mass motion as well as for the angular momentum L=2 normal modes of the Bose condensate. A mechanism of quantum evaporation forced by the rotating field is analyzed.

We study the weakly interacting Bose gas in both two and three dimensions using a variational approach. In particular we construct the thermodynamic potential of the gas to within ladder approximation and find by minimization an accurate mean-field description of the dilute Bose gas. Using spin-polarized atomic hydrogen as a specific example, we obtain an improved description of the Bose-Einstein condensed phase in three dimensions, and a signature of a phase transition in two dimensions. The latter cannot be found by a straightforward application of perturbation theory around the ideal Bose gas.

We study the interactions of a possibly dense and/or quantum degenerate gas with driving light. Both the atoms and the electromagnetic fields are represented by quantum fields throughout the analysis. We introduce a field-theory version of Markov and Born approximations for the interactions of light with matter, and devise a procedure whereby certain types of products of atom and light fields may be put to a desired, essentially normal, order. In the limit of low light intensity we find a hierarchy of equations of motion for correlation functions that contain one excited-atom field and one, three, five, etc., ground-state atom fields. It is conjectured that the entire linear hierarchy may be solved by solving numerically the classical equations for a coupled system of electromagnetic fields and charged harmonic oscillators. We discuss the emergence of resonant dipole-dipole interactions and collective linewidths, and delineate the limits of validity of the column density approach in terms of noncooperative atoms by presenting a mathematical example in which this approach is exact.

The recently proposed two-level atom bichromatic beam splitter has been shown theoretically to give exceptionally clean beam splitting in momentum space. In this paper, we investigate the first-order coherence property of this beam splitter, which is an important test of its usefulness in interferometric applications. We find that the beam splitter exhibits maximum fringe visibility of 0.3, which may be increased significantly through conditioning on certain variables. We then propose a type of atom interferometer based on this system, which has many desirable properties when compared with existing versions.

The dynamics of triatomic clusters is investigated employing two-body Lennard-Jones and three-body Axilrod-Teller potential functions. Lyapunov exponents are calculated for the total energy range of -2.70ε

We create a gray optical lattice structure using a blue detuned laser field coupling an atomic ground state of angular momentum J simultaneously to two excited states with angular momenta J and J-1. The atoms are cooled and trapped at locations of purely circular polarization. The cooling process efficiently accumulates almost half of the atomic population in the lowest-energy band, which is only weakly coupled to the light field. Very low kinetic temperatures are obtained by adiabatically reducing the optical potential. The dynamics of this process is analyzed using a full quantum Monte Carlo simulation. The calculations explicitly show the mapping of the band populations on the corresponding momentum intervals of the free atom. In an experiment with subrecoil momentum resolution we measure the band populations and find excellent absolute agreement with the theoretical calculations.

We consider three-photon–one-photon phase control of resonance-enhanced photonioization with a phase-diffusion field. As is well known, control is achieved because excitation via the fundamental field interferes with excitation via the third harmonic field, and the form of the interference (i.e., constructive or destructive) depends on the relative phase difference between the two fields. In the problem, the stochastic nature of the field influences control because the propagation constant of a dispersive medium depends on the field's fluctuating frequency. Here, we approach the influence of laser phase noise on control via (i) a physically intuitive zeroth-order approximation, (ii) first-order perturbation theory, and (iii) numerical simulation. Our results show that first-order perturbation theory is not attractive for the study of this problem, since it requires the evaluation of very high order correlation functions associated with the fundamental field"s fluctuating frequency. More importantly, however, numerical simulation demonstrates that highly efficient control can be attained even in the presence of very large linewidth fields.