The variation of the product angular distributions near isolated Lorentzian resonances is theoretically analyzed. We show that interactions between the asymptotically degenerate dissociative states can give a monotonic variation of the anisotropy parameters of $\mathrm{O}{(}^3{P}_j,\hspace{0.5em}j=0,1,2)$ with different slopes near isolated Lorentzian resonance in the predissociation of the OH molecule. The anisotropy parameters are shown to change near the resonance even in the simplest situation where the predissociation occurs through only one dissociative state, noninteracting to the first order with other asymptotically degenerate states. This finding is attributed to second- and higher-order interactions.

The photoabsorption spectrum of the C II ion has been experimentally observed using the technique of the two-laser generated plasmas. In this way, both the discrete spectrum, with the series of resonance lines converging to the ionization threshold, and the photoionization cross section above the first limit have been measured. Beyond the threshold the cross section shows several resonances corresponding to ${}^{2}S$ and ${}^{2}D$ open channels and lines corresponding to ${}^{2}P$ closed channels.

We show that atomic photoionization at all energies can be described in terms of nuclear Coulomb properties plus a limited number of atomic screening parameters. Our results support the conclusion that only screening corrections to the lowest multipoles are needed for photoionization differential cross sections. Quadrupole screening can be important except in the lightest atoms, while octupole screening is important in inner shells of intermediate-$Z$ atoms and in all shells of high-$Z$ atoms. We provide a simple way to predict in what energy ranges and for what ejection angles $\theta$ quadrupole and octupole screening effects are greatest.

We report modifications to an inversion procedure by which central and spin-orbit potentials can be determined starting with scattering phase shifts given at a fixed energy. The formalism can be used to analyze data from the scattering of projectiles with arbitrary spin and the procedure we adopt gives more accurate results than obtained before with this method.

Larger scale eigenchannel R-matrix calculations than those of Pan et al. [Phys. Rev. A 53, 840 (1996)] confirm the prediction of a 2-meV-wide resonance feature at a photon energy of 5.421 eV in the $\mathrm{Li}\mathrm{}\mathrm{}\left(3s\right)\mathrm{}$ partial cross section resulting from photodetachment of ${\mathrm{Li}}^{-}.$ This resonance was neither clearly observed nor identified in measurements of Ljungblad et al. [Phys. Rev. Lett. 77, 3751 (1996)]. We identify this resonance as a ${}_N\{\upsilon {\}}_n^A{=}_5\{1{\}}_6^{-}$ state [having angular symmetry ${\mathrm{}(K,T)\mathrm{}}^A{=(2,0)\mathrm{}}^{-}$ or ${(n}_{\lambda }{,n}_{\mu },m)=(1,7,0\left)\mathrm{}\right].$ This state, which is forbidden by propensity rules in ${\mathrm{H}}^{-}$ photodetachment, is predicted to be prominent also in the $\mathrm{Li}\mathrm{}\left(4l\right)\mathrm{}$ partial cross sections, for $l>~1.$ Besides the ${}_5\{1{\}}_6^{-}$ state, the $\mathrm{Li}\mathrm{}\left(3s\right)\mathrm{}$ partial cross section in the energy region 20–60 meV below the $\mathrm{Li}\mathrm{}\left(5p\right)\mathrm{}$ threshold is dominated by two other doubly excited states, which have been observed in ${\mathrm{H}}^{-}$ photodetachment. Our calculations are in excellent agreement with the measurements of Ljungblad et al. in the energy region from the $\mathrm{Li}\mathrm{}\left(5p\right)\mathrm{}$ threshold to 20 meV below.

We present an alternative derivation of the semiclassical limit of the scattering Coulomb wave function. The result is expressed as a sum over classical paths. Each contribution is factorized in two terms, namely the square root of the classical particle density and a phase factor corresponding to the classical action.

Using the multistep-capture-and-loss model, we carry out a theoretical analysis for the K satellite spectra emitted from Ar hollow atoms formed below the surface of a solid target, as observed by Briand et al. [Phys. Rev. A 54, 4136 (1996)]. It is found that the feature of the K x-ray spectra is mainly governed by the magnitude of the rate for the electron capture from a solid target by a highly charged ion.

We investigate which terms of the extended Bethe-Bloch equation do not follow Bragg’s rule of simple additivity of stopping cross sections when a compound is formed. Using the statistical description of the target atom, we find the dominating contribution to these chemical effects coming from the logarithmic (Bethe) term. Only a minor contribution is due to the Barkas or $Z_1^3$ term. Based upon scaling laws, both effects can be related to the variation of the mean ionization potential on forming the compound.

Francium has been the least-studied alkali-metal atom until recently. We present accurate calculations for the discrete and continuum optical transitions, and dispersion coefficients for two colliding francium atoms. Spin-orbit coupling is explicitly included and the influence of core polarization on the energies and the electric dipole operator is considered. Predictions for a range of transition amplitudes that are needed for parity violation experiments are made. The van der Waals coefficients for the long-range collision of two-ground-state Fr atoms in different fine-structure levels show a departure from an established trend in other alkali-metal atoms. We comment on the differences.

The approach of time-delay spectroscopy is proposed as a tool for the study of high-lying autoionizing states through fast laser sources.

We predict phenomena in the behavior of an ultracold, trapped gas of fermionic atoms. We find that quantum statistics radically changes the collisional properties, spatial profile, and off-resonant light-scattering properties of the atomic fermion system, and we suggest how these effects can be observed.

Strong-field single ionization and double ionization of two diatomic molecules, ${\mathrm{O}}_2$ and ${\mathrm{N}}_2,$ are studied and compared to Xe and Ar, using an intense ultrashort pulse Ti:sapphire laser in the $2\times {10}^{13}$ to $8\times {10}^{14}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ intensity range. ${\mathrm{N}}_2$ behaves like a structureless atom for both single and double ionization. The recently reported suppression of the ${\mathrm{O}}_2^{+}$ ion yield compared to ${\mathrm{Xe}}^{+}$ is confirmed in our experiment, but we show that the suppression is not due to dissociative recombination. Rather, we conclude that the ionization rate of ${\mathrm{O}}_2$ is below that predicted by tunneling ionization. We extend the study to the double ionization of ${\mathrm{O}}_2$ and find a distinctly reduced nonsequential double-ionization rate. We find evidence that electronic structure influences strong-field tunneling ionization in molecules.

A scheme is presented that allows quantum-noise-limited, background-free signal detection in high-resolution spectroscopy, atom-light interferometers, and optical clocks. The method combines the electron-shelving technique with a removal of all absorbers not participating in the excitation scheme. Application to the ${}^1{S}_0{-}^3{P}_1$ transition of Ca demonstrated a more than fourfold improvement of the signal-to-noise ratio with respect to the previous photon shot-noise limit.

A field-quantized electromagnetic propagator description emphasizing the spatial localization of light emitted from a single-electron atom is presented. With the aim of obtaining a better insight into the quantum electrodynamics in the near-field zone of the atom, two approaches, formally different but equivalent in respect to their physical predictions, are studied. From the Maxwell equations, among the transverse operators, a transverse propagator picture in which the source region for the field is identified with the spatial domain occupied by the transverse current density of the atom emerges. In this picture the field propagation is isotropic and always retarded. By identifying the source region with that of the total atomic current, the transverse propagator becomes anisotropic, and attains a nonretarded self-field part and a near-field part different from zero only for spacelike events. By changing the Coulomb Lagrangian, a nonrelativistic Hamiltonian formalism adequate for reconciling the photon concept with the anisotropic propagator picture is introduced. In this formalism the transverse self-field energy is transferred to the particle Hamiltonian, and the interaction Hamiltonian now includes an interaction between the retarded field and the transverse self-field dynamics. The link between the standard (nonpropagator) theory, often used to argue that the total electromagnetic field is always retarded, and the transverse propagator theory is established. The equivalence between the two approaches is proved by demonstrating that the standard theory in fact includes a nonretarded response in the spatial domain occupied by the longitudinal part of the induced atomic current density.

Both quantum mechanics and stochastic-process theory deal with dynamical systems the behaviors of which can be predicted only probabilistically. It is shown here that the measurable behavior of an elementary quantum system can be modeled as a non-Markovian stochastic process. The conclusion that quantum behavior can generally be modeled as a real stochastic process eliminates some mysterious characteristics of quantum mechanics when viewed in Copenhagen-interpretation terms.

The state-dependent-diagonalization (SDD) method is applied to the eigenvalue problem of an asymmetrical quantum sextic anharmonic oscillator with the potential energy $V\left(x\right)=\frac{1}{2}{x}^2+{\sum }_{j=3\mathrm{}}^6{A}_j{x}^j,$ where $A_6>0.\mathrm{}$ This method treats the eigenstates individually and is especially efficient for the high excited states. Three representative potentials have been examined: (a) $A_j=1,$ (b) $A_j=10,$ and (c) the $A_j’\mathrm{s}$ are chosen to fit the vibrational potential energy of the hydrogen molecule. By the SDD method, the eigenfunction and eigenvalue of each of the first 100 eigenstates of the above potentials can be accurately determined by diagonalizing matrices of sizes less than $95\times 95.$ Results for the thermal variations of the heat capacity and the first six cumulants of the vibrational displacement are also presented.

Duality is considered for the perturbation theory by deriving, given a series solution in a small parameter, its dual series with the development parameter being the inverse of the other. A dual symmetry in perturbation theory is identified. It is then shown that the dual to the Dyson series in quantum mechanics is given by a recently devised series having the adiabatic approximation as leading order. A simple application of this result is given by rederiving a theorem for strongly perturbed quantum systems.

We derive a general WKB energy splitting formula in a double-well potential by incorporating both phase loss and the anharmonicity effect in the usual WKB approximation. A bare application of the phase loss approach to the usual WKB method gives better results only for large separation between two potential minima. In the range of substantial tunneling, however, the phase loss approach with the anharmonicity effect considered leads to a great improvement in the accuracy of the WKB approximation.

The geometric phases of the cyclic states of a generalized harmonic oscillator with nonadiabatic time-periodic parameters are discussed in the framework of squeezed state. It is shown that the cyclic and quasicyclic squeezed states correspond to the periodic and quasiperiodic solutions of an effective Hamiltonian defined on an extended phase space, respectively. The geometric phase of the cyclic squeezed state is found to be a phase-space area swept out by a periodic orbit. Furthermore, a class of cyclic states is expressed as a superposition of an infinite number of squeezed states. Their geometric phases are found to be independent of $ħ,$ and equal to $-\mathrm{}(n+1/2\mathrm{})\mathrm{}$ times the classical nonadiabatic Hannay angle.