The complex network of Floquet states that results from an application of an external ac electric field to a collection of atoms is investigated. It is shown that precision dc Stark spectroscopy can reveal the details of the quasienergy states, Floquet states, spawned by the application of a rf field. Transitions to the Floquet sidebands of quadratic (dc) Stark states are found to have absorption intensities in good agreement with theory. This combination of dc and ac fields applied to atoms, Floquet spectroscopy, is then used to determine accurately the scalar and tensor polarizabilities of the 65 ${}_{}{}^2{}_{}{}^{}\mathrm{P}$ state of sodium. Deviations from quadratic behavior are investigated as well as the relationship of our measured polarizability to previous measurements at lower principal quantum numbers.

Recent studies indicate that several bound states exist for some negative ions of the lanthanides. In this work we demonstrate that the second member of the actinide series, Th, also possesses multiple negative ion states below its ground state, consistent with the relatively high yield observed in the laboratory. Our valence space relativistic-configuration-interaction calculations predict the strongest bindings for ${\mathrm{Th}}^{\mathrm{-}}$ 6${\mathit{d}}^2$7${\mathit{s}}^2$7p J=2.5 and ${\mathrm{Th}}^{\mathrm{-}}$ 6${\mathit{d}}^3$7${\mathit{s}}^2$ J=1.5 with electron affinities (EA) of 0.365 and 0.189 eV, respectively. We also expect certain weaker candidates to exist with (${\mathit{J}}^{\left(\mathrm{\pi }\right)}$, EA (eV)): (0.$5^{\left(\mathrm{-}\right)}$,0.088), (1.$5^{\left(\mathrm{-}\right)}$,0.075), (3.$5^{\left(\mathrm{-}\right)}$,0.042), and (2.$5^{\mathrm{}(+)\mathrm{}}$,0.056), where π=+ (-) corresponds to even (odd) parity states.

The isotope shift and the hyperfine structure of 14 spectral lines of Hf i were investigated using high-resolution laser spectroscopy of a well-collimated beam of Hf atoms. The hyperfine splitting constants A and B of the electronic states ${}_{}{}^5{}_{}{}^{}$${\mathit{G}}_5$,...${,}^5$${\mathit{G}}_2$${,}^5$${\mathit{F}}_3$ of the excited configuration 5${\mathit{d}}^2$6s6p and of some electronic states of 5d6${\mathit{s}}^2$6p were obtained for the two stable odd isotopes ${}_{}{}^{177}{}_{}{}^{}\mathrm{Hf}$ and ${}_{}{}^{179}{}_{}{}^{}\mathrm{Hf}$. From these data one-electron hyperfine splitting parameters could be deduced, e.g., ${\mathit{a}}_{6\mathit{s}}$=3.08(15) GHz for the magnetic dipole part in the case of ${}_{}{}^{177}{}_{}{}^{}\mathrm{Hf}$. Our accurate experimental values of the isotope shifts between the stable Hf isotopes 174, 176–180 allow a reliable separation of the effect of the specific mass shift and of the field shift for all observed spectral lines. Using the field shift of the 545.29-nm line, which corresponds to an almost pure 5${\mathit{d}}^2$6${\mathit{s}}^{2\mathrm{-}}$5${\mathit{d}}^2$6s6p transition, the change in mean-square nuclear charge radius between ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$ and ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}$ was determined to be δ〈${\mathit{r}}^2$〉=0.098(13) ${\mathrm{fm}}^2$. Values of δ〈${\mathit{r}}^2$〉 for the Hf isotopes 174, 176, 177, and 179 referred to ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$ are also available from the present work.

Ground- and excited-state energies, as well as ionization potentials and electron affinities, are calculated for all the alkali-metal atoms Li–Fr by the relativistic Fock-space coupled-cluster method. The coupled-cluster singles and doubles approximation, which includes single and double virtual excitations in a self-consistent manner, is implemented. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point. Rather extensive basis sets of balanced Gaussian spinors are used to span the atomic orbitals. The average error for the ionization potentials is 0.09% and for excitation energies 0.2%. Electron affinities are less accurate, particularly for the heavier atoms, with errors of 4–9 % for K, Rb, and Cs.

Using the one-step, scattering formulation of resonance x-ray emission, the effect of state interference on the angular distribution and polarization of molecularly scattered x-ray photons are explored. It is shown that the polarization dependence of the scattering cross sections for resonance elastic x-ray emission can be used as a crucial tool in assigning symmetries of unoccupied levels.

We have developed a windowless, geometry-independent method for measuring the relative oscillator strengths of gases by observing phase matching in the sum-mixing process in a gas jet. The fundamental beams are focused into the gas jet. There is an optimum pressure for gas behind the inlet valve. The inverse of the optimum pressure is proved to change linearly with the inverse of the energy detuning from the measured level, and the slope of the linearity is proportional to the oscillator strength of the level. Using this method we have measured the relative oscillator strengths of some resonance levels of Xe, Kr, and Ar in the vicinity of the cutoff limit of LiF.

The deexcitation of μp and μd atoms has been simulated within a kinetics model, taking the energy dependence of cascade processes into account. The x-ray yields and the kinetic-energy distributions for the ground and excited states have been calculated. The high-energy component produced by the Coulomb deexcitation is shown to result in noticeable effects in precise x-ray spectroscopy and muonic-atom diffusion.

Valence-shell relativistic configuration-interaction calculations for ${\mathrm{Ce}}^{\mathrm{-}}$ (6p attachment to the 4f5d6${\mathit{s}}^2$ ground state) have yielded the following electron affinities (EA): (2J, EA (eV))=(9, 0.259), (7, 0.147), (5, 0.105), (3, 0.043), and (7, 0.055). We also find the electron affinity for 5d attachment in the 4f5${\mathit{d}}^2$6${\mathit{s}}^2$ 2J=7 state to be 0.178 eV. This is possibly the second species (${\mathrm{La}}^{\mathrm{-}}$ being the first) with opposite parity bound states. The existence of several bound states is consistent with the high yields of ${\mathrm{Ce}}^{\mathrm{-}}$ achieved in recent accelerator mass spectrometry experiments.

High-resolution single-electron capture spectra have been obtained for ${\mathrm{O}}^{2+}$ ions colliding with He, Ne, and Ar at 4-keV energy. For the He and Ne targets the dominant capture channels involve transitions from the ground ${}_{}{}^3{}_{}{}^{}$P state of ${\mathrm{O}}^{2+}$ to the first and second excited states ${(}^2$${\mathit{D}}^{\mathit{o}}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$) of ${\mathrm{O}}^{+}$. Eight well-resolved peaks are observed in each spectrum, corresponding to exactly the same capture channels with the target product ions (${\mathrm{He}}^{+}$ and ${\mathrm{Ne}}^{+}$) undisturbed in their ground states. One relatively intense peak observed in the Ne spectrum is attributed to capture from the quintet state of ${\mathrm{O}}^{2+}$ (2s2${\mathit{p}}^3$ ${}_{}{}^5{}_{}{}^{}$${\mathit{S}}^{\mathit{o}}$) to the ${}_{}{}^4{}_{}{}^{}$P state of ${\mathrm{O}}^{+}$(2s2${\mathit{p}}^4$ ${}_{}{}^4{}_{}{}^{}$P). The ${\mathrm{O}}^{2+}$ in the Ar spectrum exhibits an entirely different character. Eight peaks are discernible, of which five are associated with capture channels which leave the target product ${\mathrm{Ar}}^{+}$ ion in an excited state. The dominant channel is due to the ground-to-ground transition ${\mathrm{O}}^{2+}$${(}^3$P)→${\mathrm{O}}^{+}$${(}^4$${\mathit{S}}^{\mathit{o}}$) with the target ${\mathrm{Ar}}^{+}$ ion formed in its first excited state (3s3${\mathit{p}}^6$ ${}_{}{}^2{}_{}{}^{}$S).

In this paper fully ab initio calculations of the electric dipole moment (EDM) of atomic rubidium due to two possible mechanisms—the intrinsic electric dipole moment of the electron and the scalar-pseudoscalar coupling between the electrons and the nucleons—are presented. The calculations were carried out using an approach which is a hybrid of the diagrammatic many-body perturbation theory (MBPT) and the multiconfiguration Dirac-Fock method. These calculations, unlike any of the previous MBPT calculations for the rubidium atom, also take into account the effects of electron pair correlations on the atomic EDM. Our results demonstrate that these effects can make significant contributions to the EDM of alkali-metal atoms.

The two-body depolarized, collision-induced light-scattering spectrum of gaseous methane has been measured and analyzed at five temperatures from 295 to 130 K. This spectrum consists of a low-frequency component, which is due to bound dimers (${\mathrm{CH}}_4$${)}_2$, and an intermediate-frequency, purely translational contribution which is due to collisionally interacting ${\mathrm{CH}}_4$ pairs. (The high-frequency part, the rotational induced spectrum, was analyzed elsewhere and is of no great concern here.) The experimental spectra are compared with line-shape calculations based on a refined, empirical pair polarizability model and the spherical average of the Righini-Maki-Klein’s potential [Chem. Phys. Lett. 80, 301 (1981)]. At all temperatures agreement of measured and computed profiles is observed on an absolute intensity scale.

The charge-state distributions and production cross sections of Ne recoil ions produced through pure ionization, electron capture, and electron loss processes of projectile Ar ions have been determined for 1.05-MeV/amu ${\mathrm{Ar}}^{\mathrm{q}+}$+Ne (q=4, 6, 8, 10, 12, 14, and 16) collisions using a projectile-ion-recoil-ion coincidence technique. Recoil ions in low charge states, in particular, singly charged ions, are produced predominantly through pure ionization without any change of projectile charge. Electron loss or capture processes of projectiles, though weak relative to the pure ionization, are found to result in an enhancement of the multiply charged recoil ions. The average charge 〈i${\mathrm{〉}}_{\mathrm{q},\mathrm{q}\prime }$ of recoil ions in a specific process, ${\mathrm{Ar}}^{\mathrm{q}+}$+Ne→${\mathrm{Ar}}^{\mathrm{q}\prime +}$+${\mathrm{Ne}}^{\mathrm{i}+}$, is found to increase with increasing projectile charge q and with the number of the lost or capture electrons from or into projectiles.

${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ atomic polarizations following the spin-polarized electron capture process for the Na→(3s)${+}^3$${\mathrm{He}}^{2+}$ system were measured at ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{2+}{}_{}{}^{}$ impact energies from 5.33 to 9.33 keV/amu. The magnitude of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ atomic polarizations was deduced from the ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ nuclear polarization measured by means of beam-foil spectroscopy. The observed polarization transfer coefficient ${\mathit{P}}_{\mathit{T}}$ defined by the ratio of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ atomic polarization to the sodium one showed a pronounced reduction from unity, which was qualitatively explained by the prediction of a simple cascade photon decay model. Evidence for a further reduction of ${\mathit{P}}_{\mathit{T}}$ from the above model and a possible impact energy dependence of ${\mathit{P}}_{\mathit{T}}$ suggested an excessive depolarization due to the presence of the collision alignment parameter ${\mathit{A}}_0^{\mathrm{col}}$ of ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ formed by the electron capture process. In order to see this more closely, the observed ${\mathit{P}}_{\mathit{T}}$’s were examined theoretically using the semiclassical impact parameter method, in which an 18-state molecular expansion was employed, and atomic-type electron translation effects were rigorously taken into account. Ensuring that both the absolute values and the impact energy dependence of the observed capture cross sections were remarkably well reproduced by the calculations in which the states up to 4f in ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ were introduced, it was demonstrated that the calculated results for ${\mathit{P}}_{\mathit{T}}$ qualitatively reproduced not only the absolute values of the observed ${\mathit{P}}_{\mathit{T}}$’s but also their gentle decrease with increasing impact energy. Production of nuclear polarizations resulting from the polarized electron capture processes between multicharged heavy ions and alkaline-earth-metal atoms is offered as one of the promising applications to the future project of universal polarized heavy-ion sources.

The angular distribution of ${\mathit{KL}}_{23\mathrm{-}}$${\mathit{LLL}}_{23}$ Auger electrons emitted from the decay of 1s2p vacancy states of Ne doubly ionized by 700–2000-keV protons has been measured. From the measured anisotropy of the Auger lines the alignment of the double-vacancy states has been deduced. Our data compared with different theories indicate that the shake-off plays an important role in the double-ionization process at these energies.

An application of the artificial-channel method with hyperspherical coordinates to the calculation of photoionization cross sections of two-electron systems is presented. The method yields ‘‘bound-free’’ transition amplitudes and bound-state energies of any two-electron system. It obviates the separate generation of bound- and continuum-state wave functions by calculating directly the desired amplitudes. As applications, the photodetachment cross section of the ${\mathrm{H}}^{\mathrm{-}}$ ion and the photoionization cross section of the He atom have been calculated. The computations are compared with other theoretical calculations and with experiments. The results obtained are in excellent agreement with experimental results for all the energies considered. Of equal significance is the close agreement, attesting to the high accuracy of the method, between results obtained by using the length form for the field-matter interaction and those obtained with the acceleration form.

Synchrotron-radiation excited ion mass spectrometry has been used to study the 3s3${\mathit{p}}^6$np(n≥4) resonances in argon at 25.0–29.3 eV. It is shown using a time-independent resonant scattering approach that the Fano parametrization may be applied to overlapping resonances. For the Dubau-Seaton profile an exact expression of the closed-channel phase shift is obtained. We find that regarding the window character of the Ar 3s series the Fano parameters calculated using the multichannel multiconfiguration Dirac-Fock method are in good agreement with those derived from fitting a convoluted Fano function to the measured n=4 autoionizing resonance. The Fano parameters are also derived from perfect fits to the 5≤n≤8 resonances which tests the validity of this parametrization to overlapping members of an inner-valence electron resonance series. In contrast, a parametrization of the entire series based upon the Dubau-Seaton formula did not result in a good fit without modifications. Using the same value of the shape parameter we find, however, that the n=4 resonance can be accurately represented by both the Fano and Dubau-Seaton profiles.

We have carried out a series of isolated-resonance and R-matrix close-coupling calculations for the electron-impact excitation of the 3${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$S→3s3p ${}_{}{}^3{}_{}{}^{}$P transition in the Mg-like ions ${\mathrm{Ar}}^{6+}$, ${\mathrm{Ti}}^{10+}$, ${\mathrm{Fe}}^{14+}$, and ${\mathrm{Se}}^{22+}$. We obtain good agreement between the results of the two theoretical methods for three-state calculations, i.e., for the description of just a single Rydberg series of resonances. However, when two or more Rydberg series are present we observe large differences, due to interacting resonance effects, over a wide range of energies for all of the ions examined. For the case of ${\mathrm{Fe}}^{14+}$, we have continued the perturbative studies of interacting resonances of Griffin et al. [Phys. Rev. Lett. 72, 3491 (1994)] and also find the predominant effect to be due to direct configuration interaction between the resonant states rather than being due to their coupling through a common continuum. Our inclusion of these interacting resonance effects removes the major discrepancies between the perturbative and nonperturbative results for ${\mathrm{Fe}}^{14+}$ reported previously [Badnell et al., Phys. Rev. A 48, R2519 (1993)]. This is of importance for the study of indirect processes which are strongly radiation damped, for which the perturbative approach is widely used and the standard formulation of the close-coupling approximation is not applicable.

A generalized wave function is defined for an arbitrary real functional. Properties of the traversal-time wave function are investigated for one-dimensional scattering at a fixed energy. A Heisenberg-type uncertainty relation is derived from the traversal-time wave function. Traversal-time probability distributions for a Larmor clock measurement are studied in detail. The high-resolution limit of a traversal-time measurement is examined. The use of ‘‘fast’’ and ‘‘slow’’ arguments in a traversal-time analysis is discussed. The systems studied include free motion, resonance, and nonresonance tunneling through a double-δ-function potential, rectangular barrier, absorbing optical potential, and interaction with a slow oscillator.

We have measured the ΔN=1 dielectronic recombination cross sections of hydrogenlike helium. Recombination rates were investigated as ${\mathrm{He}}^{+}$ ions interacted with free electrons in the electron-cooler section of an ion storage ring. The ion beam was cooled prior to recombination, resulting in enhanced energy resolution. Fits to the 2l2l’ resonances yielded transverse and longitudinal temperatures of ${\mathit{kT}}_{\mathrm{\perp }}$=0.15 eV and ${\mathit{kT}}_{\mathrm{\parallel }}$=0.8×${10}^{\mathrm{-}4}$ eV, respectively. The resulting peak widths are approximately 0.3-eV full width at half maximum. The measured integrated cross sections are in qualitative agreement with calculated resonance strengths.

The whole-atom integral incoherent-scattering cross sections of elements Na, Cl, K, Cu, Br, Rb, Ag, Cd, I, and Hg have been derived with the aid of the mixture rule from the incoherent-scattering cross sections of their simple halides. The cross sections of the halides are extracted from their total attenuation cross sections measured by performing transmission experiments in a modified narrow-beam setup. The results are found to be in good agreement with the values assembled by Hubbell et al. [J. Phys. Chem. Ref. Data 4, 471 (1975)] that are interpolated to 661.6 keV.