A semiempirical calculation of the P-odd and P,T-odd interactions in the YbF molecule is made. As a result, the corresponding constants of the effective spin-rotational Hamiltonian of the molecule are obtained. In comparison with atoms, both P-odd and P,T-odd interactions are enhanced approximately ${10}^3$ times. For example, the electric dipole moment of the valence electron feels an internal molecular electric field of 3×${10}^{10}$ V/cm. This field is directed along the molecular axis and can be oriented by an external field ∼${10}^4$ V/cm.

In a previous paper [Phys. Rev. A 40, 6260 (1989)] the ternary absorption coefficient of hydrogen in the fundamental band was calculated with the assumption of pairwise dipole components. The comparison with measurements of the absorption showed striking disagreement, particularly at the higher temperatures, presumably due to the neglect of the irreducible ternary dipole components. We extend here the calculations by including the most important irreducible ternary dipole components. The overlap-induced part of the ternary dipole components is obtained from the one-effective electron model which is written in a form suitable to account for vibrational transitions. Two different models are compared here: one suggested by Guillot et al., J. Chem. Phys. 90, 650 (1989), and a new one. The comparison of the calculated total absorption (a sum formula) with the existing measurements shows that in hydrogen the exchange quadrupole-induced ternary dipole components are capable of producing the strong observed temperature dependence. Furthermore, it is the only mechanism presently known which may permit the reproduction of the measured data from theory; some of the approximations developed here give reasonable quantitative agreement with the measurement.

The series solution method developed by Pekeris [Phys. Rev. 112, 1649 (1958); 115, 1216 (1959)] for the Schrödinger equation for two-electron atoms, as generalized by Frost et al. [J. Chem. Phys. 41, 482 (1964)] to handle any three particles with a Coulomb interaction, has been used. The wave function is expanded in triple orthogonal set in three perimetric coordinates. From the Schrödinger equation an explicit recursion relation for the coefficients in the expansion is obtained, and the vanishing of the determinant of these coefficients provides the condition for the energy eigenvalues and for the eigenvectors. The Schrödinger equation is solved and the matrix elements are produced algebraically by using the computer algebra system maple. The substitutions for a particular atom and diagonalization were performed by a program written in the c language. Since the determinant is sparse, it is possible to go to the order of 1078 as Pekeris did without using excessive memory or computer CPU time. By using a nonlinear variational parameter in the expression used to remove the energy, nonrelativistic energies, within the fixed-nucleus approximation, have been obtained. For the ground-state singlet 1 ${}_{}{}^1{}_{}{}^{}$S state, this is of the accuracy claimed by Frankowski and Pekeris [Phys. Rev. 146, 46 (1966); 150, 366(E) (1966)] using logarithmic terms for Z from 1 to 10, and for the triplet 2 ${}_{}{}^3{}_{}{}^{}$S state, energies have been obtained to 12 decimal places of accuracy, which, with the exception of Z=2, are lower than any previously published, for all Z from 3 to 10.

The method described in the preceding paper for the solution of two-electron atoms, which was used to calculate the 1 ${}_{}{}^1{}_{}{}^{}$S and 2 ${}_{}{}^3{}_{}{}^{}$S states of helium and heliumlike atoms within the fixed-nucleus approximation, has been applied to the case where all three particles are in relative motion. The solutions in the present case automatically include the effects of the mass polarization term and are compared with the results obtained for the term by using first-order perturbation theory with the fixed-nucleus wave functions. The input data for a particular atom consist of the atomic number, as before, but now the corresponding mass of the nucleus must be given also. Nonrelativistic energies with the nuclear mass included in the calculation have been obtained for the 1 ${}_{}{}^1{}_{}{}^{}$S and 2 ${}_{}{}^3{}_{}{}^{}$S states for Z ranging from 1 to 10. The energy with the nucleus in motion can be expressed only to eight significant figures (SF’s) given the accuracy with which the relevant physical constants are known at present. All the results given here are computed as if these constants were known to ten SF’s so that errors not incurred due to rounding. Convergence of the energies to ten SF’s for both the singlet and triplet state was reached with a matrix of size 444 for Z values from 2 to 10. Convergence for the ${\mathrm{H}}^{\mathrm{-}}$ ion was a little slower.

Transitions between the Zeeman substates of Cs 6 ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{1/2}^{}{}_{}{}^{}$ and Rb 5 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ atoms, induced in collisions with He atoms, have been investigated experimentally by methods of atomic fluorescence spectroscopy. The collision process has also been studied theoretically with time-dependent perturbation theory. Cs or Rb vapor contained in a quartz cell together with helium at low pressure was selectively excited by pulsed dye-laser radiation to the ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2,\mathrm{-}1/2}$ Zeeman substate in a magnetic field ranging from 1.5 T to 7 T. The fluorescence spectrum, consisting of components emitted from the directly excited state and from the collisionally populated state, was resolved with a Fabry-Pérot interferometer. Measurements of the relative intensities of the fluorescence components yielded the Zeeman mixing cross section for Cs-He and Rb-He collisions. It was found that the Cs 6 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ cross section varied approximately as ${\mathit{B}}^2$ in the range 0<B<0.76 T, showed a much weaker field dependence in the range from 0.76 T to 5 T, where it peaked, and declined slightly at B>5 T. The Rb 5 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ cross section did not exhibit any variation with B. A theoretical calculation of the Cs cross section carried out using time-dependent perturbation theory explains the magnetic-field enhancement in terms of the minute magnetic-field-induced mixing of the ${\mathit{P}}_{1/2}$ and ${\mathit{P}}_{3/2}$ states and the resulting breaking of time-reversal symmetry. The results of the calculation are in good agreement with the experimental results at fields in the range 0<B<5 T.

In this work are considered two quantum-mechanical approaches to treat a single-coordinate (Eckart-type) potential scattering process. The one approach is based on the application of Toeplitz matrices and the other on the application of negative imaginary (absorbing) potentials. It was found that for this type of ‘‘reactive’’ process, the method based on the Toeplitz matrices performed better.

We consider the problem of charge-state-correlated cross sections in the 1.05-MeV/nucleon ${\mathrm{Ar}}^{\mathit{q}+\mathrm{-}}$Ar collision system with q=10–16. Theoretical results from a semiclassical (ħ=0) shell model that treats the Ar(L) and Ar(M) shells in an uncoupled approximation are compared with recent experimental measurements. For the dominant channels agreement can be obtained within a factor of 2–3, but larger disagreements remain in the direct multiple-ionization channel for recoil charges above 8 and generally for the multiple-capture (MC) channels. The experimental data are analyzed to understand whether in principle they are compatible with an independent-particle model evaluation. Single-particle capture and ionization probability functions are found that describe the experimental MC cross sections.

The Schrödinger equation of the hydrogen atom in an intense monochromatic radiation field is solved numerically exactly by applying the Floquet close-coupling method. Intensity dependence of the rates of ionization in the region of adiabatic stability is determined. Their dependence on the principal quantum number, on the angular momentum, and on the magnetic quantum number is investigated at λ=1064, 620, and 248 nm. The calculated critical parameters show good agreement with the independent calculations of Potvliege and Smith [Phys. Rev. A 48, R46 (1993)]; those for the hydrogenic 5g circular state are consistent with the results of the first observation of stability in the Ne atom by de Boer et al. [Phys. Rev. Lett. 71, 3263 (1993)]. In connection with the ongoing experiments in the H atom, these parameters and the calculated ionization rates in the stability region can provide stringent quantitative tests of the basic Floquet ansatz, which underlies a wide class of ab initio theories of matter-light interaction.

The study of photoelectron satellites in the near-threshold region is important for differentiating among various electron correlation mechanisms. For CO, which is a prominent test case for theories describing electron correlation effects, the threshold and near-threshold branching ratios (BR’s) of the K-shell satellites were measured. Eight different C 1s satellite states were identified, showing very complex threshold behavior. The resonancelike behavior of the (2σ${)}^{\mathrm{-}1}$(1π${)}^{\mathrm{-}1}$(2${\mathrm{\pi }}^{\mathrm{*}}$${)}^1$(S’=1) satellite BR agrees with recent theoretical calculations. The observed energy dependence of the singlet (2σ${)}^{\mathrm{-}1}$(1π${)}^{\mathrm{-}1}$(2${\mathrm{\pi }}^{\mathrm{*}}$${)}^1$ satellite compares less well with the calculations. Three ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ satellites with a (2σ${)}^{\mathrm{-}1}$(5σ${)}^{\mathrm{-}1}$(nσ${)}^1$ configuration have a constant satellite BR over the energy range studied. Three 2σ satellites, which have been assigned as pure conjugate shake-up states, have intensity only near threshold. The threshold spectrum above the O 1s ionization threshold consists of two distinct groups of satellites. Conjugate shake-up transitions contribute to the intense feature centered at 551-eV binding energy, which is not observed above its threshold. Two ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ satellites, which have been described by configuration interaction of (1σ${)}^{\mathrm{-}1}$(5σ${)}^{\mathrm{-}1}$(nσ${)}^1$ states with a singlet π${\mathrm{\pi }}^{\mathrm{*}}$ state, show indications of shape-resonance-like behavior.

Differential cross sections and generalized oscillator strengths have been measured for two optically allowed transitions 2${\mathit{p}}^6$${(}^1$${\mathit{S}}_0$)→2${\mathit{p}}^5$${(}^2$${\mathit{P}}_{1/2,3/2}$)3s and the optically forbidden transition 2${\mathit{p}}^6$${(}^1$${\mathit{S}}_0$)→2${\mathit{p}}^5$${(}^2$${\mathit{P}}_{1/2}$)3p in Ne. These measurements are carried out for electron kinetic energies 300, 400, and 500 eV at small scattering angles (θ=2.4°–33.7°) by means of electron-energy-loss spectroscopy. Optical oscillator strengths have been determined by extrapolating the generalized oscillator strengths to zero momentum transfer, as (0.137±0.018) and (0.0106±0.0014), for the 2${\mathit{p}}^5$${(}^2$${\mathit{P}}_{1/2}$)3s and 2${\mathit{p}}^5$${(}^2$${\mathit{P}}_{3/2}$)3s states, respectively. Integrated cross sections have been calculated by integrating the differential cross sections for each impact energy. The errrors are estimated to be less than 13%.

A merged-beams electron-energy-loss technique is described, by which absolute cross sections can be measured for near-threshold electron-impact excitation of multipy charged ions. Results are reported here for absolute total electron-impact excitation cross sections for the ${\mathrm{O}}^{5+}$(2s→2p) transition from below threshold to 1.6 eV above threshold. The experimental data are in good agremeent with a seven-state close-coupling calculation throughout the energy range of the experiment. Results agree with calculations showing that more than 90% of the electrons causing excitation are ejected in the backward direction in the center-of-mass frame. This backscattering is shown in both quantum-mechanical and semiclassical calculations. Evidence is observed for high-lying metastable autoionizing states with a lifetime of approximately 0.9 μs which are made to ionize by electron impact.

The target continuum has a large effect on electron and positron scattering to low-lying states of atoms. In addition to ionization the continuum of positron scattering includes positronium-formation channels. The equivalent-local coupled-channel-optical method is a numerically simple way of including the continuum in a coupled-channel calculation. Here it is tested by its prediction of total cross sections for continuum and discrete excitations on inert-gas targets.

We report the results of a depolarized interaction-induced light-scattering (DILS) experiment on gaseous neon at room temperature, from which the two- and three-body induced spectra have been extracted. The two-body spectrum is in excellent agreement (in absolute units) with a previous determination by Frommhold and Proffitt [Phys. Rev. A 21, 1249 (1980)], while the three-body spectrum is a new result. The comparison of the three-body experimental spectral moments with a calculation performed within the pairwise additivity approximation shows a discrepancy which is of opposite sign to that observed in krypton. The calculations have been carried out including the first-order correction of the Wigner-Kirkwood expansion in order to take into account quantum effects. We suggest that the occurence of irreducible three-body effects may be due to more than one microscopic mechanism and these can be usefully investigated by means of DILS spectroscopy.

A high-energy-resolution study of the dissociative recombination of ${\mathrm{HeH}}^{+}$ has been performed. A theoretical analysis has indicated that the recombination at low energy is due to the presence of a metastable triplet-state component of the ion beam.

L-subshell ionization cross sections of Au and Bi induced by ${\mathrm{C}}^{2,3+}$ and ${\mathrm{O}}^{3+}$ ions have been measured for impact energies ranging from 0.25 to 0.79 MeV/u. The data have been compared with the predictions of the ECPSSR [perturbed-stationary-state (PSS) theory with energy-loss (E), Coulomb deflection (C), and relativistic corrections (R)] theory. Reasonable agreement between theory and experiment is observed for the ${\mathit{L}}_1$(2${\mathit{s}}_{1/2}$) and ${\mathit{L}}_3$(2${\mathit{p}}_{3/2}$) subshells. For the ${\mathit{L}}_2$(2${\mathit{p}}_{1/2}$) subshell, however, large disagreement between the data and the ECPSSR predictions persists. This difference could be due to the ‘‘collision-induced intrashell’’ mechanism that was suggested by Sarkadi and Mukoyama [J. Phys. B 14, L255 (1981)].

We present in this communication the results of the distorted-wave Born approximation calculations of the electron-pair-production cross section by using the technique of Wright, Sud, and Kosik [Phys. Rev. C 36, 562 (1987)] for 6.0-MeV photons on Z=1, 30, 50, 68, 82, and 92. The calculated cross sections are compared with the interpolated experimental data and the results obtained from the existing interpolating formulas.

We study radial wave packets produced by short-pulsed laser fields acting on Rydberg atoms, using analytical tools from supersymmetry-based quantum-defect theory. We begin with a time-dependent perturbative calculation for alkali-metal atoms, incorporating the atomic-excitation process. This provides insight into the general wave-packet behavior and demonstrates agreement with conventional theory. We then obtain an alternative analytical description of a radial wave packet as a member of a particular family of squeezed states, which we call radial squeezed states. By construction, these have close to minimum uncertainty in the radial coordinates during the first pass through the outer apsidal point. The properties of radial squeezed states are investigated, and they are shown to provide a description of certain aspects of Rydberg atoms excited by short-pulsed laser fields. We derive expressions for the time evolution and the autocorrelation of the radial squeezed states, and we study numerically and analytically their behavior in several alkali-metal atoms. Full and fractional revivals are observed. Comparisons show agreement with other theoretical results and with experiment.

We present a theoretical study of the relativistic effect of atomic radiative processes. In order to avoid any entanglement of the atomic screening effect, we would like to elucidate the relativistic effect of the atomic radiative processes by examining the radiative processes of the hydrogenlike atomic ion system. We discover a type of ‘‘zero’’ at which the electric dipole matrix element vanishes for nκ→εκ’ transitions with ‖κ‖=‖κ’‖ owing to the relativistic retardation effect. Such a ‘‘zero’’ serves as a precursor of a transition of the photoionization cross section from nonrelativistic behavior to relativistic behavior.

The momentum-space calculation of electron-molecule elastic scattering is described and illustrated as the first step in a program of electron-molecule scattering that takes all reaction channels into account. The method is the analog for molecules of the integral-equation methods that have had essentially complete success for structurally simple atoms. Although scattering is a single-center problem in momentum space its multicentered nature in coordinate space results in the integral equations for different orbital angular momenta being coupled. There are no restrictions in principle on the nature of the target molecule. For illustrative purposes the static exchange calculation is supplemented by a phenomenological polarization potential that will be replaced by an ab initio optical potential and coupled electronic channels in the planned development of a general scattering method.

The energies, intensities, and angular anisotropies of the Ne KL-LLL satellite Auger lines have been studied by the multiconfiguration Dirac-Fock method. In addition to the initial- and final-state correlation effects we have studied the influence of the quantum beat effect on this Auger spectrum. Since the energy splitting of the Ne 1${\mathit{s}}^{\mathrm{-}1}$2${\mathit{p}}^{\mathrm{-}1}$ ${}_{}{}^3{}_{}{}^{}$P multiplet is much smaller than the lifetime broadening, the coherent excitation of these initial states by the in time and space localized electromagnetic pulse of the projectile has a drastic effect on the angular distribution of Auger electrons. To analyze this coherence effect we have generalized the theory of the angular distribution of Auger electrons to the case of coherent excitation of partially overlapping initial states. The results of our calculations are in good overall agreement with experiment. However, for a quantitative study of the influence of the coherence and the initial spin state on the anisotropy of these Auger lines new measurements with lower error limits are necessary.