An 81-channel hyperspherical close-coupling calculation has led to a photodetachment spectrum of ${\mathrm{H}}^{\mathrm{-}}$ in excellent agreement with experiments at energies up to threshold for the production of H(n=7), including all the observed resonance structures. Positions of Wannier ridge resonances not only for ${\mathrm{H}}^{\mathrm{-}}$ but also for He and ${\mathrm{Li}}^{+}$ are fitted to a double-Rydberg formula, and the screening parameter in it is found to be remarkably independent of the nuclear charge.

Measurements of the stopping power of large multiply charged ions were made by determining energy losses in thin aluminum films directly coated on solid-state detectors. With initial projectile velocities in the range of (1–5)×${10}^7$ cm/sec, the stopping power per amu of albumin (molecular weight M∼66290) and cytochrome c (M∼12400) increases quadratically in velocity to a maximum value of seven times that estimated for isolated atomic nitrogen moving with the same velocity. The observed velocity dependence of the stopping power is in qualitative agreement with the one derived from a one-dimensional shock model. Pressures estimated from the measured stopping power using the model are hundreds of megabars. The results show evidence of the collective interaction that results possibly from ‘‘hydrodynamic’’ shock behavior in plasmas formed by the coherent collision of high-velocity biopolymer atoms with target atoms.

Four laser beams traveling in the same direction that split and reflect a thermal calcium atomic beam compose an atomic interferometer like the Mach-Zehnder optical interferometer. The interference performance of the atomic interferometer was examined by changing the phase of the induced dipole moment in the atomic wave due to the laser beams, or the phase of atomic ‘‘wavepacket’’ in an atomic trajectory due to the ac Stark effect. An interference signal with a visibility of more than 15% was obtained. This interferometer will be useful in the detection of weak signals that require a long integration time, since it is less sensitive to the fluctuation of the laser frequency compared with the optical Ramsey atomic interferometer.

We show that the time profile of the harmonics emitted by a single atom exposed to a strong electromagnetic field may be obtained through a wavelet or a Gabor analysis of the acceleration of the atomic dipole. This analysis is extremely sensitive to the details of the dynamics and sheds some light on the competition between the atomic excitation or ionization processes and photon emission. For illustration we study the interaction of atomic hydrogen with an intense laser pulse.

A 64.4% reduction in absorption at the rubidium D2 line is observed when a pumping field at 775.8 nm is tuned on resonance to the transition between the excited states 5${\mathit{P}}_{3/2}$ and 5${\mathit{D}}_{5/2}$. As the pumping field is tuned off resonance, an absorption peak appears at the side of the Doppler-broadened D2 line. This modification in absorption is related to pumping-induced atomic coherence in this three-level ladder-type system. This experiment is done in a Rb vapor cell at room temperature and with cw diode lasers for both pumping and probe beams in a Doppler-free configuration.

A proof is given, which relies on the commutator algebra of the unitary Lie groups, that quantum gates operating on just two bits at a time are sufficient to construct a general quantum circuit. The best previous result had shown the universality of three-bit gates, by analogy to the universality of the Toffoli three-bit gate of classical reversible computing. Two-bit quantum gates may be implemented by magnetic resonance operations applied to a pair of electronic or nuclear spins. A ‘‘gearbox quantum computer’’ proposed here, based on the principles of atomic-force microscopy, would permit the operation of such two-bit gates in a physical system with very long phase-breaking (i.e., quantum-phase-coherence) times. Simpler versions of the gearbox computer could be used to do experiments on Einstein-Podolsky-Rosen states and related entangled quantum states.

The final-state distribution of hydrogen, acted upon by a 1/2-cycle pulse, has been calculated semiclassically for a proposed one-dimensional experiment. This work was motivated by the recent experimental realization of half-cycle pulses by Jones, You, and Bucksbaum [Phys. Rev. Lett. 70, 1236 (1993)] in which preliminary studies of ionization and state redistribution for hydrogenlike atoms were carried out. To simplify the situation theoretically, an experiment is proposed in which an additional weak static electric field is imposed and approximately one-dimensional states are selected. Within this one-dimensional approximation the transition probability to various n states (n is the principal quantum number) has been calculated as a function of the amplitude of the half-cycle pulse, using a semiclassical formula due to Miller [Adv. Chem. Phys. 25, 69 (1974)]. A complete derivation of this formula and a discussion of approximations are made in the following paper. We have found that an even number of trajectories always contributes to the transition probability and leads to observable interference effects. In addition, we find that bifurcations of these trajectories can occur, resulting in resonances and more complicated interference structures.

In this paper we derive the expression for the transition coefficient used in the preceding paper [C. D. Schwieters and J. B. Delos, Phys. Rev. A 51, 1023 (1995)] for principal-quantum-number transitions in one-dimensional hydrogen caused by half-cycle pulses. We briefly review the methods of Miller [Adv. Chem. Phys. 25, 69 (1974)] and Marcus [Chem. Phys. Lett. 7, 525 (1970); J. Chem. Phys. 54, 3965 (1971)], and then derive the result using the methods of Maslov and Fedoriuk [Semi-Classical Approximation in Quantum Mechanics, (Reidel, Dordrecht, 1981)]. Also, we examine the approximate reduction of hydrogen from three to one dimension and we find a hitherto unknown correction due to the residual motion of one of the ignored degrees of freedom. We discuss the regime of validity of this one-dimensional approximation.

The 3${\mathit{p}}^{\mathrm{-}1}$→5${\mathit{s}}^1$ resonant excitation energy and decay width of Kr atoms are calculated by an ab initio Green’s-function method. The dipolar relaxation energy shift of the 3${\mathit{p}}^{\mathrm{-}1}$→5${\mathit{s}}^1$ resonantly excited state of Kr atoms is predominantly due to the 3${\mathit{p}}^{\mathrm{-}1}$5${\mathit{s}}^1$→3${\mathit{d}}^{\mathrm{-}2}$5${\mathit{s}}^1$ɛf super-Coster-Kronig (sCK) spectator decay process. The calculated excitation energies are overestimated by about 1.0 eV. The decay widths for 3${\mathit{p}}_{1/2}^{\mathrm{-}1}$→5${\mathit{s}}^1$ and 3${\mathit{p}}_{3/2}^{\mathrm{-}1}$→5${\mathit{s}}^1$ resonantly excited states are 2.08 and 1.88 eV, respectively. They are larger than the decay widths of the 3${\mathit{p}}_{1/2}^{\mathrm{-}1}$ and 3${\mathit{p}}_{3/2}^{\mathrm{-}1}$ core-level ionized states. The increase of the decay width is a result of the decrease of 3${\mathit{p}}^{\mathrm{-}1}$5${\mathit{s}}^1$→3${\mathit{d}}^{\mathrm{-}2}$5${\mathit{s}}^1$ɛf sCK spectator decay and the increase of 3${\mathit{p}}^{\mathrm{-}1}$5${\mathit{s}}^1$→3${\mathit{d}}^{\mathrm{-}1}$4s(p${)}^{\mathrm{-}1}$5${\mathit{s}}^1$ɛp(d) CK spectator decay. The changes of the (s)CK decay rates are due to the screening of the final two-hole-state potential by the resonantly excited 5s electron.

The 3 ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$←X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$ and 3 ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$←X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$ band systems of ${\mathrm{K}}_2$ are studied by the polarization-labeling spectroscopy method. An observation of isotope shifts of rotationally resolved lines in both systems reveals that the previous vibrational numbering in the 3 ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ and 3 ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$ states is incorrect by 1 and 3 vibrational quanta, respectively. An analysis is carried out for both states. We present the resulting molecular parameters that describe the 3 ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ state to 55% and the 3 ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$ state to 71% of their potential well depths.

The valence photoemission spectra (valence hole spectral functions) of the titanium halides ${\mathrm{TiF}}_4$, ${\mathrm{TiCl}}_4$, and ${\mathrm{TiBr}}_4$ are calculated by an ab initio Green’s-function method. For ${\mathrm{TiCl}}_4$, the agreement with experiment is good. For the other Ti halides it is predicted that the valence hole spectral functions are very similar to the one for ${\mathrm{TiCl}}_4$. The spectral functions are shifted toward smaller binding energy by a fairly constant amount with a decrease of the ligand electronegativity. The constant spectral energy shift reflects the Koopmans theorem eigenvalue shifts by the ligand electronegativity change.

The intensities of the electric quadrupole transitions in the x-ray spectra of the 3d-transition-metal monoxide diatomic molecules were calculated using the discrete variational method of the local-density approximation. The quadrupole transition intensities have been found to be negligible for the left-hand-side 3d metal oxides. It was shown that the electric quadrupole transitions can appreciably contribute to the MK${\mathrm{\beta }}_5$ emission spectra of the right-hand-side 3d metal oxides, along with the dipole transitions.

An asymptotic expansion due to Menzel and Pekeris [Mon. Not. R. Astron. Soc. 96, 77 (1935); reprinted in Selected Papers on Physical Processes in Ionized Plasma, edited by D. H. Menzel (Dover, New York, 1962)] has been used to give a series expansion for the bound-bound and bound-continuum oscillator strengths. For the bound-bound transitions between the initial and final principal quantum numbers n and n’, and for any n and n’ considered, the oscillator strength is within 0.5% accuracy of the exact values. For the bound-continuum oscillator strength, and continuum energies ɛ≤1 Ry, the accuracy is better than 1%. For ${\mathit{n}}^2$ɛ≫1, the method of Menzel and Pekeris is inapplicable. Using an alternative method, an expansion in terms of n and ɛ is derived that gives the oscillator strength within 1% accuracy.

The superposition-of-configurations (SOC) method is used to calculate intershell and core-correlation corrections to energy levels for the low-lying states of Be and ${\mathrm{B}}^{+}$ belonging to the configurations 2${\mathit{s}}^2$, 2s2p, and 2${\mathit{p}}^2$ and the singlets of 2s3s and 2s3d. The wave functions are also used to calculate the oscillator strengths for all allowed transitions among these states. Transition energies are calculated with an accuracy ranging from 10 to 50 ${\mathrm{cm}}^{\mathrm{-}1}$ and the oscillator strengths are estimated to be accurate to 1–2 %. The SOC wave functions are single- and double-substitution calculations based on a multiconfiguration referent, where the reference set is derived from a two-electron natural-orbital transformation of valence-shell-correlated SOC functions. It is found that a fairly substantial reference set is necessary to obtain these results, ranging from three configuration-state functions (CSFs) for 2s2p ${}_{}{}^3{}_{}{}^{}$P and 2${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$P to 11 CSFs for 2s3s ${}_{}{}^1{}_{}{}^{}$S. Intershell correlations are necessary for both energy differences and oscillator strengths, but core correlations with angular symmetries higher than l=1 (p orbitals) are not.

An estimation of the radius of convergence of the 1/Z expansion (Z is the charge of the nucleus) for the ground state of the two-electron atom is obtained. The calculation is based on an idea that, with certain conditions being satisfied, the radius of convergence of the 1/Z series can be estimated with good precision if one constructs the function λ(f), inverse to the function f(λ)=[E(λ)-${\mathit{E}}_0$]/${\mathit{E}}_1$ (E is energy, λ=1/Z, while ${\mathit{E}}_0$ and ${\mathit{E}}_1$ are the first two coefficients of the perturbation expansion of the energy). We find numerically that the nearest singularity to f=0 in the complex f plane of the inverse function λ(f) is at the point f=0.8 corresponding to the threshold point E=-0.5. a.u. We find also that the series for the inverse function λ(f) converges at this point. We discuss the nature of the singularity of the inverse function λ(f). The value for the radius of convergence of the 1/Z expansion of the ground state of a He-like ion obtained is ${\mathit{R}}_{\lambda }$=1.097 660 79, which we think to be the most accurate value presently available.

We investigate, theoretically and experimentally, the onset of modified electronic precession due to quasimolecular behavior in dense atomic gases. The close connection between the angular coupling of collision pairs and a modification of the Faraday effect is pointed out. We have observed the onset of this quasimolecular modification of the atomic Faraday effect with high-resolution laser measurements of the absorption and Faraday spectra near the ${\mathit{D}}_2$ line of Rb atoms immersed in high-density buffer gases. The atomic Faraday effect itself is also affected by the presence of nuclear spin; this modifies the electronic precession through angular-momentum coupling. We describe how to separate the effect of nuclear spin from the effects due to quasimolecular behavior. In this way we establish the existence of angular coupling of the Rb valence electrons to neighboring buffer-gas atoms at densities above ∼2×${10}^{19}$ ${\mathrm{cm}}^{\mathrm{-}3}$ in Xe buffer gas. In He buffer gas, quasimolecular modifications of the Faraday effect are approximately two times smaller than for Xe.

In a previous paper [Phys. Rev. A 49, 3322 (1994)] we reported on a three-photon excitation study of odd (in ${\mathit{j}}_{\mathit{c}}$l coupling notation nl’[K${]}_{\mathit{J}}$, in which the angular momentum of the ion core ${\mathit{j}}_{\mathit{c}}$ is coupled to the orbital momentum of the Rydberg electron l to give K, which is then coupled to the electron spin to give J) ns’[1/2${]}_1$, nd’[3/2${]}_1$, nd’[5/2${]}_3$, and ng’[7/2${]}_3$ autoionizing series of atomic argon, krypton, and xenon. Here, four-photon excitation of even autoionizing Rydberg states of these rare gases between the ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{3/2}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ ionic limits has been investigated using multiphoton ionization and supersonic expansion techniques. In all atoms the np’[1/2${]}_0$, np’[3/2${]}_2$, nf’[5/2${]}_2$, and nf’[7/2${]}_4$ autoionizing series have been observed. Such states have never been observed before in argon, while in krypton and xenon our experimental conditions have enabled a considerably more accurate and extended investigation than previously possible. The analysis of the resonance line shapes and intensities has allowed for a detailed investigation of the four-photon ionization dynamics, in particular with respect to the role of the three-photon virtual level.

This paper presents a formalism for studying semianalytically the development of a multiparticle quantum-mechanical system outward from its center of mass, casting its dynamics in terms of hyperspherical coordinates which emphasize collective motions of all constituents. The formalism expresses the system’s devleopment through an R matix which varies with the system’s hyperradius R, incorporating a greater amount of the dynamics as R grows. Eigenvalues of the R matrix are further transformed into R-dependent phases whose R variation elucidates interactions between alternative degrees of freedom. An initial application to the ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}^{\mathit{e}}$ states of helium reveals details of interactions hitherto concealed within numerical treatments.

The contribution of nuclear polarization to the Lamb shifts of bound electrons in the 1${\mathit{s}}_{1/2}$, 2${\mathit{s}}_{1/2}$, and 2${\mathit{p}}_{1/2}$ states is considered for various even-A nuclei (230≤A≤252 with 90≤Z≤98). Utilizing the concept of effective photon propagators with nuclear polarization insertions, the effective self-energy shifts due to virtual excitation of collective nuclear rotational and vibrational states and of the dominant giant dipole resonance are calculated. The formalism is extended to odd-Z nuclei for which the effective interaction is derived within the single-particle approach. While the corresponding energy shifts of the 1${\mathit{s}}_{1/2}$ state represent a considerable correction, the contribution to the 2s-2p splitting is comparable to the current accuracy of high-precision experiments.

The necessity of using projection operators to avoid mixing of positive and negative energy Dirac eigenstates in multiconfiguration Dirac-Fock calculations is discussed. It is shown that convergence problems observed at high Z or when the magnetic interaction was introduced in the self-consistent field (SCF) process are completely due to the absence of such projection operators in previous calculations. It is found that the presence of negative energy states prevented the diagonal Lagrange parameters (orbital energies) of correlation orbitals to approach -∞ when their weights became very small, thus causing the SCF process to fail without projection operators. A method for implementing these projection operators in Dirac-Fock programs is described. A detailed study of the effect of the introduction of projection operators, and of the self-consistent magnetic interaction in the ground state of heliumlike ions is reported. The relative importance of higher-order effects and second-order quantum electrodynamics effects is discussed.