A quantitative analysis of the results of a recent Coulomb-explosion experiment with ${\mathrm{He}}_2^{2+}$ is described. Using the adiabatic potential curve predicted for the ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$ ground state of this relatively simple dication, a Monte Carlo simulation of the Coulomb-explosion process was performed. The results show that such methods can faithfully reproduce the experimental results when accurate potential-energy surfaces are available. The implications for more complex systems are discussed.

Cross sections have been measured for the production of H(3l) atoms via electron transfer in proton-helium collisions from 25 to 100 keV. In the experiment, the intensity of Balmer-α radiation is measured as a function of proton energy. These measurements are combined with previously measured density matrices for the same collision to produce relative cross sections. Our relative electron-transfer results, accurate to 3–7 %, are normalized to the absolute ${\mathrm{\sigma }}_{3\mathit{s}}$ cross-section measurement of Brower and Pipkin [Phys. Rev. A 39, 3323 (1989)] at 60 keV. Comparison of our ${\mathrm{\sigma }}_{3\mathit{l}}$ cross-section measurements with other experimental measurements shows general agreement to within 20%, with larger differences for older results. The recent calculation of Shingal and Lin [J. Phys. B (to be published)] agrees to within 13% of our measurement of ${\mathrm{\sigma }}_{3\mathit{s}}$ above 30 keV, but predicts a low-energy oscillatory behavior of ${\mathrm{\sigma }}_{3\mathit{p}}$ and ${\mathrm{\sigma }}_{3\mathit{d}}$ not present in experimental results.

Time-dependent and time-independent measurements of emissions from Xe in Kr-Xe mixtures are reported. Kr host gas pressure was varied from 100 to 900 Torr, and Xe impurities were varied from 1% to 10% of total Kr pressure. This work has shown that the Xe${(}^3$${\mathit{P}}_1$) resonant state is depopulated by collisions with both Xe and Kr ground-state atoms. In particular, a two-body quenching rate of 10 ${}_{}{}^4{}_{}{}^{}\mathrm{P}_{\mathrm{Xe}}^{}{}_{}{}^{}$+2100${\mathit{P}}_{\mathrm{Kr}}$ is reported. This two-body rate is assigned to represent a collisional transition to the Xe${(}^3$${\mathit{P}}_2$) metastable state. A three-body rate of 97${\mathit{P}}_{\mathrm{Xe}}$${\mathit{P}}_{\mathrm{Kr}}$+7${\mathit{P}}_{\mathrm{Kr}}^2$ was also found. The rate 7${\mathit{P}}_{\mathrm{Kr}}^2$ is assigned to represent the formation of (KrXe${)}^{\mathrm{*}}$ molecules, while the rate 97${\mathit{P}}_{\mathrm{Xe}}$${\mathit{P}}_{\mathrm{Kr}}$ represents either formation of ${\mathrm{Xe}}_2^{\mathrm{*}}$(${\mathrm{O}}_{\mathit{u}}^{+}$) or (XeKr${)}^{\mathrm{*}}$. Time-dependent measurements made in the Xe first continuum region at about 1500 Å indicate that these emissions follow the Xe${(}^3$${\mathit{P}}_1$) state.

The electron capture to continuum states of the projectile cusp electron distributions are measured in the collisions of 30-keV ${\mathrm{H}}^{+}$ ions with He, Ne, and Ar, and are analyzed by Legendre polynomials. The value of ‖${\mathit{B}}_2^0$/${\mathit{B}}_0^0$‖ shows a dependence on the target.

Cross sections for nonresonant transfer excitation (NTE) are calculated for collisions of ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ with ${\mathrm{H}}_2$ (2H) and He targets in the 50–500-keV impact-energy range. Single-electron capture probabilities to the 2s and 2p orbitals of He and single-electron excitation probabilities for ${\mathrm{He}}^{+}$ (1s→2s or 2p) transitions are independently computed, as a function of impact parameter, using the semiclassical multichannel-impact-parameter model with an expansion in atomic orbitals placed either on one or both centers. NTE cross sections for the (2${\mathit{s}}^2$${)}^1$S, (2${\mathit{p}}^2$${)}^1$D, and (2s2p${)}^1$P states, computed in the independent-electron model, are compared with the recent high-resolution electron data for transfer excitation into these states. For ${\mathrm{He}}^{+}$+${\mathrm{H}}_2$ collisions, NTE is found to contribute primarily at the low collision energies, dropping off at the higher energies. On the contrary, for the symmetric ${\mathrm{He}}^{+}$+He collisions, NTE cross sections do not drop off with impact energy as expected. In the case of the (2${\mathit{p}}^2$${)}^1$D state, an increase in the cross section, similar to the experimental data, is seen. However, in both cases, the calculated cross section seems to be larger than the experimental data.

We propose a different way for selecting the outgoing continuum basis functions needed in complex Kohn variational calculations of electron-molecule scattering. The proposed method is based on the recent work of Sun et al. [Phys. Rev. A 41, 4857 (1990)] dealing with dynamically prepared basis sets for algebraic variational calculations. We have found an alternative technique for removing the sensitivity to the traditional cutoff function in calculations involving ionic targets, while retaining all the computational simplicity of the complex Kohn method.

An attempt is made to solve the spherical Raman-Nath equation taking electron spin into account. Spin effects are discussed for a free-electron laser in the extreme case ${\mathit{v}}_{\mathit{b}}$≃c, where c is the speed of light and ${\mathit{v}}_{\mathit{b}}$ the velocity of the electron.

Free-electron laser operation with a circularly polarized wiggler and an appropriately directed axial magnetic field of suitable strength is shown to generate significant coherent emission of radiation into higher frequencies.

The wavelengths of the 2${\mathit{S}}_{1/2}$-2${\mathit{P}}_{1/2,3/2}$ transitions for five Z=24 to 34 lithiumlike ions have been measured with an accuracy of about 50 ppm. These results can be combined with a recent multibody perturbation calculation to determine the remaining QED effects in these three electron ions with an uncertainty of about 0.2–0.6%. The observed QED effects are in agreement with a one-electron calculation that uses a screened nuclear charge.

Nonadiabatic wave functions obtained including the effect of strong nuclear interaction by means of the R-matrix theory were used to compute the initial sticking fractions for the S states of tdμ. The standard sticking formula was suitably generalized to allow the application of the wave functions defined only outside the nuclear surfaces. The initial sticking fractions are found to be 0.917×${10}^{\mathrm{-}2}$ for the ground state and 0.915×${10}^{\mathrm{-}2}$ for the first excited state, and are about 3% larger than the values obtained neglecting the effects of nuclear forces. Our results agree with the most recent experimental data. This agreement indicates that the number of fusions per muon achieved in current experiments is close to the theoretical limit.

Gold-metal dissociation energies measured by mass-spectroscopic methods in 1967 by Gingerich and co-workers showed unexpectedly high ${\mathit{D}}_{\mathit{e}}$ values compared with those of the corresponding copper and silver compounds. In the past, this has been explained in terms of the increased ionicity of the diatomic gold compounds on the basis of the Pauling model. In fact, the very high dissociation energies observed for AuLa and AuLu arise from relativistic effects, as shown by calculations of nonrelativistic and relativistic configuration interactions. The expected overall trend in the group-11 series is also explained (bond stabilities: AuM≫CuM>AgM, M any metal atom) in terms of relativistic effects and new spectroscopic data are given for AuLa and AuLu.

The detection of ${\mathrm{Cu}}^{+}$ and ${\mathrm{Cu}}^{2+}$ ions, after excitation of the M shell of atomic copper in the 40–125-eV photon energy range (with synchrotron radiation) has allowed us to point out a preferential decay of the Rydberg states 3${\mathit{p}}^5$3${\mathit{d}}^{10}$4snd (and ns) into double-ionization channels (3${\mathit{d}}^9$,3${\mathit{d}}^8$4s final ionic states) in contrast with the relaxation of the valence resonance 3${\mathit{p}}^5$3${\mathit{d}}^{10}$4${\mathit{s}}^2$ into single-ionization ways (satellite 3${\mathit{d}}^8$4${\mathit{s}}^2$εl channels).

Partial cross sections and angular-distribution asymmetry parameters of diagram and satellite lines associated with Li 1s photoionization were measured using synchrotron-radiation excitation. Special emphasis was given to a high-resolution study of the ${}_{}{}^1{}_{}{}^{}$P and ${}_{}{}^3{}_{}{}^{}$P conjugate shakeup satellite lines testing qualitative predictions of the conjugate shakeup model: increasing σ and decreasing β values towards threshold, both being verified. Comparison with recent relaxed Hartree-Fock calculations shows good agreement for the ${}_{}{}^1{}_{}{}^{}$P satellite, but demonstrates also that the present theory does not seem to be able to describe the cross-section behavior of the ${}_{}{}^3{}_{}{}^{}$P satellite correctly.

Differential cross sections (DCS) for the 1 ${}_{}{}^1{}_{}{}^{}$S-2 ${}_{}{}^3{}_{}{}^{}$S excitation in helium have been measured with a high angular resolution of about 1° as a function of the scattering angle θ from 12° to 0° for the incident energies of 200 and 500 eV. For the incident energy of 500 eV, the DCS increases drastically as the angle decreases in the angular range smaller than 4° and reaches a value 0.075 ${\mathit{a}}_0^2$/sr at θ=0°, the increase being nearly 3 orders of magnitude. The DCS at zero scattering angle for impact energies from 200 to 800 eV have been measured. The DCS’s are found to be about 1 order of magnitude greater than those of published measurements by Skerbele, Harshbarger, and Lassettre [J. Chem. Phys. 58, 4285 (1973)] and Klump and Lassettre [J. Chem. Phys. 62, 1838 (1975)].

We investigate the neutralization of protons scattered from a clean Al(111) surface under grazing incidence for projectile energies ranging from 50 keV to 1.25 MeV. The neutral fraction of the scattered beam strongly depends on the state of preparation of the target surface and monotonically decreases with increasing projectile energy. The fractions are generally smaller than observed after transmission through thin aluminun foils. Our experimental data do not agree with recent theoretical predictions claiming dominant contributions of second-order Thomas scattering to neutralization.

We report laser spectroscopic results that extend the precision of earlier measurements substantially and provide tests of recent calculations on the singlet S, P, and D levels of atomic helium. We have determined the Lamb shift of the He 2${\mathrm{}}^1$${\mathit{S}}_0$, 3 ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ states by unambiguously establishing the 2 ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ absolute level position, by Doppler-free, two-photon transitions from 2 ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ to ${\mathit{n}}^1$${\mathit{D}}_2$ (7≤n≤20). The Lamb shift of 0.093 761(5) ${\mathrm{cm}}^{\mathrm{-}1}$ [2810.88(15) MHz] agrees with a less precise experiment of Sansonetti, Gillaspy, and Cromer [Phys. Rev. Lett. 65, 2539 (1990)], but differs from theory by 98.36(15) MHz. In combination with the above-noted experimental result, the Lamb shift of the 3 ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ level is 0.000 522(45) ${\mathrm{cm}}^{\mathrm{-}1}$, in agreement with theory. Our relative spacings of the D levels is in disagreement with published theoretical calculations, but is in agreement with recent unpublished corrections of this work. This D-level agreement also confirms Casimir forces to the 2% level.

By exploiting the approximate SU(2) symmetry of the m=0 quadratic Zeeman Hamiltonian within multiplets of fixed principal quantum number, the dynamics is mapped onto a twofold hindered rotor. This allows a singularity-free uniform semiclassical quantization of Solov’ev’s approximate integral of the motion to be performed. Excellent agreement with quantum results is obtained.