A methodology is developed combining many-body-perturbation theory and close coupling of final-state channels with multiconfiguration Hartree-Fock theory to calculate photoionization cross sections of open-shell atoms with accurate threshold and resonance energies. Photoionization calculations of the ground ${1s}^2{2s}^2{2p}^6{3s}^2{3p}^6{3d4s}^{2}D$ state of atomic Sc, the first of the transition metals, are performed from threshold to 60 eV using this method. All single-electron transitions from $4s,$ $3d,$ and $3d$ subshells are included. Over a broad region of energy, the cross section is dominated by the strength of the $3\overrightarrow{p}3d$ resonances which are split into nine distinct transitions through the angular momentum coupling with the open shells. The total cross section and the $3\overrightarrow{p}3d$ resonances are presented in detail and reasonably good agreement with available experiment, for both energies and cross section, is obtained. Classifications of a number of the $3\overrightarrow{p}3d$ resonances are proposed. In the low-energy region, good agreement with a previous R-matrix calculation is found.

A simple statistical model is formulated to predict inclusive distributions and correlations of fragments from highly excited ${\mathrm{C}}_{60}.$ Sequential decay of excited fragments produced in an initial binary fragmentation are taken into account. A qualitative account of results from a recent experiment is achieved.

A three-dimensional lattice solution of the time-dependent Schrödinger equation for low quantum states $(n<~3)$ is combined with classical trajectory Monte Carlo results for high quantum states $(n>~4)$ to predict total electron loss and total charge-transfer cross sections for proton collisions with atomic hydrogen at intermediate energies. The total charge-transfer cross sections range from 5% above to 10% below the furnace target measurements of McClure [Phys. Rev. 148, 47 (1966)], while the total electron-loss cross sections range from 5% to 15% above the pulsed crossed-beams measurements of Shah, Elliot, and Gilbody [J. Phys. B 20, 3501 (1987)]. The calculation of ionization as a difference between electron loss and charge transfer leads to theoretical ionization cross sections that are 10% to 35% larger than the crossed-beams measurements of Shah and Gilbody [J. Phys. B 14, 2361 (1981)] and Shah, Elliott, and Gilbody [J. Phys. B 20, 2481 (1987)].

Total and partial recombination cross sections for ${\mathrm{F}}^{6+}$ are calculated using close-coupling and distorted-wave theory. For total cross sections, close-coupling and distorted-wave results, which include interference between the radiative and dielectronic pathways, are found to be in good agreement with distorted-wave results based on a sum of independent processes. Total cross sections near zero energy are dominated by contributions from low-energy dielectronic recombination resonances. For partial cross sections, the close-coupling and distorted-wave theories predict strong interference for recombination into the final recombined ground state ${1s}^2{2s}^2{}^1{S}_0$ of ${\mathrm{F}}^{5+},$ but only weak interference for recombination into the levels of the ${1s}^{2}2s2p$ configuration.

We present calculated total cross sections and product state distributions for the dissociative recombination of ${\mathrm{HeH}}^{+}$ with electrons in the high-energy resonance region. The dissociation dynamics were calculated by the solution of the time-dependent Schrödinger equation for seven coupled resonance states. The resonance curves and autoionization widths were obtained from a complex Kohn variational calculation. We compare several models for the nonadiabatic coupling. The effect of different isotopic combinations of the ${\mathrm{HeH}}^{+}$ ion on the total and partial cross sections is examined, and a prediction of the cross section for ion-pair formation is made.

The random-phase approximation (RPA) is applied to study nondipole corrections to the angular distribution of photoelectrons from the $n=2\mathrm{}$ shell of Ne. Calculations of the parameters ${\gamma }_{\mathrm{nl}}$ and ${\delta }_{\mathrm{nl}}$ arising from $E_1-E_2$ interference effects are carried out for the $2s$ and $2p$ subshells of Ne in the photon energy range 100–2000 eV. For the $2s$ shell, the RPA calculations show small effects of correlation near the $2s$ threshold energy, but are otherwise in agreement with independent-particle approximation (IPA) calculations. The RPA and IPA values of ${\gamma }_{2s}$ are also in agreement with experiment. For the $2p$ shell, a small difference between RPA and IPA calculations of the nondipole parameters is found for energies near the $1s$ threshold; however, both RPA and IPA calculations of the parameter ${\gamma }_{2p}+3\mathrm{}{\delta }_{2p}$ disagree significantly with experimental measurements for photon energies above 1000 eV.

The partial photoionization cross sections for the outer p subshell of the ground state of bromine are calculated in all available open channels as determined by LS coupling for photon energies from the ${}^{3}P$ to ${}^{1}S$ thresholds. The electron correlations which are important in this case have been taken into account using the multiconfiguration Hartree-Fock approximation for the bound and the continuum wave functions. The resonance structures between the ${}^{3}P$ and ${}^{1}D$ threshold and between the ${}^{1}D$ and ${}^{1}S$ threshold have been identified. In order to compare with experiment a frame transformation is applied to transform the LS dipole matrix elements to jj coupling. The calculated energy positions for the autoionizing resonances ${4p}^4{(}^{1}D)md,$ ${4p}^4{(}^{1}D)ns$ and ${4p}^4{(}^{1}S)md$ and ${4p}^4{(}^{1}S)ns$ are compared with recent experimental measurements, and are found to be in excellent agreement.

The $\mathrm{LS}$ states belonging to the configurations ${2s}^2{2p}^3,$ ${2s2p}^4,$ ${2s}^2{2p}^{2}3s,$ ${2s}^2{2p}^{2}3p,$ ${2s}^2{2p}^{2}3d$, and ${2s}^2{2p}^{2}4s$ of neutral nitrogen are considered in the calculations of excitation energies and oscillator strengths. Extensive configuration interaction wave functions are used, which give excitation energies in close agreement with the experiment. The calculation of the differential and integral cross sections of the forbidden ${}^4{S}^o{-}^2{D}^o$ transition for the scattering of electrons from atomic nitrogen is performed in a 11-state close-coupling approximation using the R-matrix method in the energy region from threshold to 70 eV. The calculated differential cross sections are peaked in the backward direction and compare very well with the recent measurement. The present integral cross sections also show very good agreement with the available other calculations and measurement.

The breakup of $n=3\mathrm{}$ Rydberg states of the triatomic hydrogen molecule into three $\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ atoms was studied using SRI’s fast neutral beam photofragment spectrometer. A beam of fast metastable ${\mathrm{H}}_3$ $2p{}^2{A}_2^{″}\mathrm{}(N=K=0\mathrm{})\mathrm{}$ molecules was generated by charge transfer of ${\mathrm{H}}_3^{+}$ ions in Cs vapor. The metastable beam was crossed by an intracavity dye laser beam in order to selectively prepare the $3s{}^2{A}_1^{\prime }(N=1,$ $K=0)$ and $3d{}^2{E}^{″}(N=1,$ $G=0,$ $R=1)$ states of ${\mathrm{H}}_3.$ Correlated fragment pairs were detected by a time- and position-sensitive detector. For both excited states, the two-body decay into ${\mathrm{H}+\mathrm{H}}_2$ fragment pairs as well as the three-body breakup into three correlated $\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ fragments are open channels. The two processes produce distinguishable events on the time- and position-sensitive detector. For three-body decay, only two of the three products are detected. An extensive model using physically reasonable assumptions was developed in order to explain the observed spectra and to gain insight into the kinematics of the three-body breakup. Branching ratios between three- and two-body decay are estimated for the breakup of the ${\mathrm{H}}_3$ $3s{}^2{A}_1^{\prime }(N=1,K=0)$ and $3d{}^2{E}^{″}(N=1,G=0,R=1)$ states, and compared to results of a two-dimensional wave-packet calculation.

Eigenchannel R-matrix calculation results are presented for the photodetachment partial cross sections of ${\mathrm{Na}}^{-}$ for energies up to the $\mathrm{Na}\mathrm{}\left(5p\right)\mathrm{}$ threshold. The photoelectron angular distribution asymmetry parameter for the process ${\mathrm{Na}}^{-}+\overrightarrow{\gamma }\mathrm{Na}{\mathrm{}\left(3p\right)+e}^{-}$ is also presented over the same energy range. Detailed analyses and identifications of ${}^1{P}^o$ resonance structures are presented and compared with corresponding ones in ${\mathrm{H}}^{-}$ and ${\mathrm{Li}}^{-}$. Our results are compared with works of others, including the four-state close-coupling results of Moores and Norcross [Phys. Rev. A 10, 1646 (1974)], the resonances observed by Johnston and Burrow [Phys. Rev. A 51, 406 (1995)] in studies of temporary negative ion formation in electron scattering by Na atoms, and the recent relative $\mathrm{Na}\mathrm{}\left(4s\right)\mathrm{}$ partial cross-section measurements of G. Haeffler et al. [following paper, Phys. Rev. A 59, 3655 (1999)].

We have used a collinear laser-ion beam apparatus to investigate the partial cross section for the photodetachment of ${\mathrm{Na}}^{-}$ via the $\mathrm{Na}{\mathrm{}\left(4s\right)+e}^{-}\left(\epsilon p\right)$ channel. The measured cross-section spectrum is compared to a recent R-matrix calculation [C.-N. Liu and A. F. Starace, preceding paper, Phys. Rev. A 59, 3643 (1999)]. The photodetachment cross section was measured in the energy range 4.657–4.880 eV. In this spectrum, we have identified four resonances that converge on the $\mathrm{Na}\mathrm{}\left(4d\right)\mathrm{}$ threshold. The energies and widths of the resonances were determined from the measured cross section. A semiempirical formula has also been used to predict the positions of the four resonances and to show that, in a semiclassical model, the resonances belong to the same ${}^1{P}^o$ series.

The hyperfine-state-selected scattering properties of potassium atoms at ultralow temperatures are calculated using interaction potentials gleaned from an analysis of recent photoassociation data. We predict that the small, probably negative value of the ${}^{39}\mathrm{K}$ triplet scattering length will hamper efforts to produce a Bose-Einstein condensate, unless experiments utilize a broad, accessible magnetic Feshbach resonance. The large positive value calculated for the ${}^{41}\mathrm{K}$ triplet scattering length makes it a better candidate for condensation at zero magnetic field. The fermionic isotope ${}^{40}\mathrm{K}$ is also predicted to have a large, positive scattering length for elastic collisions between spin states of experimental interest, implying that it can be efficiently evaporatively cooled to the quantum degenerate regime. In addition, certain spin states possess Feshbach resonances that may enable tuning of its interatomic interactions, possibly leading to the formation of Cooper pairs.

A multistep laser excitation scheme was used to access the last, least bound levels close to the lowest asymptote $3s+3s$ with the molecular states $X{}^1{\Sigma }_g^{+}$ and $a{}^3{\Sigma }_u^{+}$ of ${\mathrm{Na}}_2$. All singlet levels within the last $10\hspace{0.5em}{\mathrm{cm}}^{-1}$, and some triplet levels with sufficient singlet admixture, were observed. The level energies were determined with uncertainties of less than 22 MHz with respect to the dissociation limit. The hyperfine structure was resolved, and asymmetric line shapes due to predissociation by tunneling through the rotational barrier or electronic state coupling were recorded for levels above the dissociation limit.

The soft x rays produced by resonant transition radiation from a multilayer target with a submicrometer period were measured. The target consisted of 176-nm-thick nickel as radiators and 221-nm-thick carbon as spacers alternately stacked on a SiN membrane. The target was bombarded by 15-MeV electrons, and the angular dependence of the resulting x-ray spectra was measured. The spectra had a clear single peak at energies from 2 to 4 keV depending on the observation angle. The spectral dependence on the incident angle of the electron beam was also measured, and a shift of the peak energy was observed. These experimental results showed a good agreement with theoretical estimations. These results are clear evidence of single-mode resonant transition radiation.

First-principles calculations based on the generalized gradient corrected density-functional theory reveal that iron tetraoxide $\left({\mathrm{FeO}}_4\right),$ in spite of its closed-shell structure, has an electron affinity that is larger than that of any known halogen atom. This novel property is shown to be a manifestation of the special bonding characteristics of d-electron systems and can play an important role in chemical and biological processes.

We have used a first-principles, density-functional-based method to calculate the electric polarizabilities and dipole moments for several low-energy geometries of Si clusters in the size range $10<~N<~20$. The polarizability per atom is found to be a slowly varying, nonmonotonic function of N. Over this size range the polarizability appears to be correlated most strongly to cluster shape and not with either the dipole moment or the highest occupied–lowest unoccupied molecular-orbital gap. The calculations indicate that the polarizability per atom for Si clusters approaches the bulk limit from above as a function of size.

Structural stability and energetics of lutetium microclusters ${\mathrm{Lu}}_n(n=3\mathrm{}-147)$ have been investigated by molecular-dynamics simulations. An empirical model potential energy function has been parametrized for the lutetium element by using the dimer interaction potential energy profile of ${\mathrm{Lu}}_2$, which is calculated by the relativistic density functional method. Stable structures of the microclusters for $n=3\mathrm{}-13$ have been determined by a molecular-dynamics simulation. It has been found that lutetium microclusters prefer to form three-dimensional compact structures. Molecular-dynamics simulations have also been performed for spherical lutetium clusters generated from hcp crystal structure with sizes $n=33\mathrm{}-147$.

The pseudoseparation of the center of mass and relative motion of a hydrogen atom in crossed electric and magnetic fields led to a theoretical prediction of highly extended states localized in the outer potential well. These states correspond to an almost macroscopic separation between a proton and an electron, and give rise to giant dipole moments. In the present work we describe a simple, experimentally feasible, scheme for the preparation of a hydrogen atom in a superposition of such states. The preparation scheme is based on a two-step switching on of an external electric field, in the course of which the relative motion is trapped in the outer well. On the basis of classical simulations we suggest the experimental parameters at which trapping is achieved extremely efficiently.

A transfer-matrix technique is formulated to treat the scattering of a particle incident on a piecewise constant potential and interacting with an oscillatory field. A study of tunneling through a single barrier shows in the transmission probabilities, for absorption or emission of quanta from the field, replicas below the barrier of the overbarrier field-free transmissivity, with its resonant structure. In the case of resonant tunneling through a double barrier, an appropriate choice of parameters gives evidence for a change in the regime, with inhibition of transmission at a resonance energy of the intermediate well when the period of the field approaches the lifetime of the resonant state. The technique can be extended to treat scattering of a particle by more general potentials in the presence of an oscillatory perturbation. As an illustrative example, the transmissivity as a function of a bias potential in a double-barrier structure is calculated.

We present an optical pumping scheme by which atomic spin motion can be controlled without photon absorption in the fast pumping limit. The phenomenon can be understood in terms of the quantum Zeno effect and the interaction-free measurement in a spin-photon system.