Born-Oppenheimer potential-energy curve and adiabatic corrections for the 4s ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$ state of the hydrogen molecule have been computed using an explicitly correlated wave function in elliptic coordinates. It is shown that, in contrast to the Born-Oppenheimer results, the adiabatic potential-energy curve for this state is characterized by a double-minimum function. The energies of the vibrational levels and rotational constants have also been computed. Large and irregular differences have been found between thoeretical and experimental results.

Doubly excited states (DES) of heliumlike systems are studied within the coupled-channel hyperspherical adiabatic approach. The results of the multichannel calculations of the ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}^{\mathit{e}}$ and ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$ DES of ${\mathrm{H}}^{\mathrm{-}}$ and He converging to the second (n=2) threshold are presented and compared with those found in literature.

We study the performance of a simple l-dependent but otherwise local electron–noble-gas potential consisting of the direct electrostatic terms plus a 1/${\mathit{r}}^4$ polarization potential, which merges into a constant for r≤${\mathit{r}}_0$, ${\mathit{r}}_0$ depending on the target atom and the partial wave. This simple one-parameter potential reproduces low-energy elastic-scattering data by helium, neon, and argon, as well as the most advanced and sophisticated ab initio calculations. In a partial wave containing at least one occupied single-particle state in the target atom, the condition that the highest-lying bound state in the local potential has maximum overlap with the corresponding Hartree-Fock single-particle state of the atom, may serve as criterion for determining ${\mathit{r}}_0$.

We consider the one-photon excitation of atomic hydrogen by electron impact in the presence of a homogeneous monochromatic linearly polarized electric field as a model for the radiation field of the laser. In the framework of the approximative approach of Faisal and Rahman [in Fifth International Conference on Atomic Physics, edited by R. Marrus, M. H. Prior, and H. A. Stutgart (University of California, Berkeley, 1976), p. 49], suited for high-energy electrons, we present an analytic expression for the transition amplitude to an arbitrary nlm state, in terms of hypergeometric Gauss and Appell ${\mathit{F}}_1$ functions, together with the numerical results for excitation to the n=4 states.

We report observations of extremely energetic electrons produced in collisions between keV ${\mathrm{He}}^{+}$ and ${\mathrm{Ar}}^{+}$ and different solid surfaces, with energies up to approximately 40% of the center-of-mass energy. This emission can result from the decay of many-electron excitations produced in nearly head-on collisions.

A previously reported spectral theory [Phys. Rev. A 44, 3023 (1991)] is used to analyze the existence of a highly density-dependent asymmetry in the rotational lines of the far-infrared spectrum of HCl in Ar at 162.5 K and densities between 100 and 480 amagat. This asymmetry is explained in terms of dispersive components due to considering mixing effects between lines. In particular, the rotational lines making up the spectrum have a super-Lorentzian (sub-Lorentzian) shape in the low- (high-) frequency side.

We examine the Volkov limit in the interaction of an atom with an ultrastrong laser field, where the atom-laser coupling energy becomes larger than the atomic binding energy. The full time-dependent wave function is expressible as an expansion in the atomic potential. Numerical results are obtained for the ionization probability of a one-dimensional δ-potential model atom, for which full dynamical solutions are also found. We find uniform convergence toward full ionization with increasing field strength, with no sign of ground-state stabilization.

We examine similarities and differences in three schemes that are capable of producing complete population transfer in multistate systems: generalized π pulses, adiabatic passage by pulse chirping, and counterintuitive pulses or stimulated Raman adiabatic passage. We use the picture of adiabatic following through avoided crossings of instantaneous eigenvalues to exhibit the essential differences between the latter two procedures.

The dynamics of the Jaynes-Cummings interaction of a two-level atom interacting with a single mode of a radiation field prepared in a Glauber-Lachs state is investigated to study the development of seemingly chaotic oscillations of the atomic inversion from a regular collapse-and-revival phenomenon, as the field statistics is changed from the coherent state to the thermal state. The effect of thermal photons on the coherent light is shown to be striking: Both the photon distribution as well as the atomic inversion are highly sensitive to even a very small addition of thermal photons to an initially coherent radiation field. We also compare the collapse and revival occurring in the micromaser case with the Glauber-Lachs version of the Jaynes-Cummings model.

We obtain solitary-wave solutions for a nonlinear directional coupler including the effects of strong two-photon absorption. These results show that complete optical switching is possible and the pulse shape and energy are preserved.

Following a recent paper by De Brito and Baseia [Phys. Rev. A 40, 4097 (1989)], the generation of squeezing is examined for a harmonic oscillator when a sudden change of mass takes place. The correspondence of such oscillators with the radiation field and some related results, such as modulation of squeezing, are also considered.

We present an alternative way to study the polarization-dynamics equations for light propagation in anisotropic media showing up to third-order nonlinearity when the light-beam intensity is conserved. We classify systematically the possible cases and show a simpler way to find the exact solutions.

Lichten, Shiner, and Zhou [Phys. Rev. A 43, 1663 (1991)] have stated that their precision measurements of Rydberg states of helium confirm the existence of intra-atomic Casimir forces. This interpretation misidentifies the Casimir-force shift, which in fact is too small to be detected with their present level of accuracy.

Quartic anharmonic oscillators with dissipation and external force terms are studied in the semiclassical approximation. The equilibrium states are related to the quantum states by ratios of the semiclassical to quantum scales in length, action, and energy. The ratios give a measure of the departure of semiclassical from quantum invariants. In three cases semiclassical chaos is found to occur with the destruction of the equilibrium states and/or semiclassical invariants, but the quantum states are not destroyed. The fourth case is anomalous.

A scaling analysis of a variety of nonlinear equations for surface growth is presented. It predicts the existence of universal scaling functions and amplitude ratios for the surface width w(L,t) on length scale L at time t and for the height-difference correlation function G(x,t). This analysis is applied to the Kardar-Parisi-Zhang (KPZ) equation for driven interface growth in d=2, in order to derive explicit scaling forms for the amplitudes associated with the scaling of the surface width, correlation function, and saturation velocity as a function of the hydrodynamical parameters in the KPZ equation. A mode-coupling calculation that estimates the values of the various universal amplitude ratios, as well as the associated universal scaling functions is also presented. Our predictions are confirmed by simulations of three different surface-growth models in d=2 from which the amplitude ratios as well as the universal scaling function for the surface width w(L,t) (for the case of periodic boundary conditions) are numerically determined. These results are also supported by numerical integration of the KPZ equation in d=2. The universality of the height-fluctuation distribution function is also discussed. Our scaling analysis is expected to be useful in the analysis of experiments and in the study of a variety of models of surface growth as well as in establishing a more detailed connection between continuum surface-growth equations and microscopic models.

Attractors which are not chaotic but nevertheless display ‘‘strange’’ geometric properties have been the subject of a number of studies since they were studied in certain quasiperiodically forced maps, by Grebogi et al. [Physica 13D, 26 (1984)]. The attractors, as defined by these authors, are nonchaotic, since they are characterized by Lyapunov exponents which are smaller than zero; but are, however, strange since they display geometric properties unlike either limit cycles or quasiperiodic attractors. The attractors are produced by dissipative, nonlinear systems which are driven by two periodic external forces whose frequencies are incommensurate. Strange nonchaotic attractors have been observed in numerical experiments with a variety of bistable and monostable nonlinear oscillators as well as in one ingenious experiment, designed by Ditto et al. [Phys. Rev. Lett. 65, 533 (1990)], using a forced, free standing beam whose mechanical properties could be externally controlled by magnetic fields. We study here a nonlinear oscillator with a multistable potential both numerically and with an analog simulator. The dynamics mimics that of the internal magnetic flux through an underdamped, multistable, superconducting quantum interference device which is quasiperiodically forced. We report measurements and numerical computations of the power spectra, invariant density, and Poincaré sections. Precision numerical computations were used to study the Lyapunov exponents and to observe the destruction of a chaotic attractor and its replacement by a strange nonchaotic one.

The topological space of a bound conservative quantum system is studied in reference to the corresponding integrable one with the concept of parallel transport. A scheme of iterative perturbation is proposed. The destruction of invariant subspaces due to the singular behavior at avoided crossings is carefully investigated. It is shown that before the first avoided crossing the invariant subspaces are merely distorted, and after the first avoided crossing the invariant subspaces begin to be destroyed.

The Carmeli-Nitzan approach to the theory of activated rate processes is generalized to allow for different frictions in the well and barrier regions. Many previous results are recovered as special cases and some new results are obtained and discussed.

The dynamics of particle or quasiparticle motion in a molecular adiabatic dimer with site-dependent nonlinear polaronic coupling has been investigated in both coherent and dissipative regimes. An analysis of equations of motion for the Bloch-vector components has been performed. Our results show that the character of coherent dynamics is strongly influenced by nonlinear coupling. Exact conditions for self-trapping and transfer oscillations have been derived. It was shown that dissipative dynamics, particularly the character of the steady state, is determined by the condition of detailed balance in accordance with thermodynamics. For a degenerate molecular dimer it was shown that, irrespective of a strong decrease of the energy of a site due to strong nonlinear polaronic coupling, the symmetry breaking in the asymptotic distribution does not occur.