Ionization of helium target atoms by ${\mathrm{He}}^{+}$ projectiles at energies of 0.125 to 3.0 MeV/u (v=2.2–11 a.u.) has been investigated. Ratios of double-to-single ionization are determined for projectiles undergoing no charge change, electron capture, or electron loss, respectively, and cross sections for target single and double ionization are determined for projectiles undergoing no charge change or electron capture. Total cross sections for single-electron capture and loss by the incident ${\mathrm{He}}^{+}$ projectiles are also determined. The present measurements extend to higher velocities than earlier results obtained by other investigators. As found by other investigators, the double-to-single-ionization ratios associated with projectiles undergoing electron capture or loss are significantly larger than those associated with no projectile charge change. The effective charges for target single and double ionization by ${\mathrm{He}}^{+}$ projectiles are determined by normalizing to single- and double-ionization cross sections, respectively, for ${\mathrm{H}}^{+}$ projectiles. For direct target ionization, i.e., ionization associated with no projectile charge change, the double-to-single-ionization ratios for ${\mathrm{He}}^{+}$ and ${\mathrm{He}}^{2+}$ projectiles are nearly equal at equal velocities. This implies that the cross sections for single and double ionization by ${\mathrm{He}}^{+}$ are altered by the same factor when compared to fully stripped ${\mathrm{He}}^{2+}$, a result which is consistent with the fact that the effective charges for single and double ionization are about the same.

Absolute measurements of the total double-electron detachment (DED) cross sections for 3- to 50-keV ${\mathrm{H}}^{\mathrm{-}}$ ions incident on helium atoms and for 5- to 50-keV ${\mathrm{H}}^{\mathrm{-}}$ ions incident on neon and argon atoms are reported in this paper. The present DED cross sections are in better agreement with the previously reported DED cross sections for helium targets than for either neon or argon targets. A semiempirical calculation of the double detachment cross sections for the intermediate-energy collision region is also presented in this paper.

An approximate representation of the transition amplitude for the Compton-type inelastic scattering of a photon by a neutral atom is derived that is valid for low frequencies of the scattered photon. The standard low-frequency approximation accounts for the emission of the soft photon by an electron after it has been ejected from the atom; the transition amplitude thus obtained is proportional to the matrix element for photoionization and behaves as the inverse of the soft-photon energy. A correction to this approximation is derived here that includes the contribution arising from the transition of the excited atom from one resonant state to another nearby state, accompanied by the emission of a low-frequency photon. The resonances are assumed to belong to a Rydberg series formed from the temporary binding of an electron to the residual core in an excited state. A simplified model based on this picture is developed. Substantial deviations from the standard low-frequency approximation due to resonance effects are seen in a numerical study of the model.

We calculated numerically in a relativistic partial-wave formulation the positron energy-angle distributions of pair production in the fields of atoms with atomic number Z=1, 6, 13, and 82 for photons of energies near threshold, k=2.001, 2.01, and 2.10${\mathit{m}}_{\mathit{e}}$${\mathit{c}}^2$. Our partial-wave results show that in this low photon energy region, the atomic-electron screening effect for the positron energy-angle distributions increases as Z increases, k decreases, and the positron energy ${\mathit{E}}_{+}$ decreases. The ratio of the screened to the point-Coulomb positron energy-angle cross section is almost independent of the positron angle. That is, the shape of positron energy-angle distributions is almost independent of the screening. This suggests that the screening is primarily a normalization effect. Our results also indicate that the Born approximation prediction for the shape of positron energy-angle distributions is better than its prediction for positron energy spectra of pair production. The form of the Born approximation suggests a simple way to parametrize the shape of positron energy-angle distributions.

Electric-field effects on the N=2 Feshbach resonances (both resonance positions and widths) of ${\mathrm{H}}^{\mathrm{-}}$ are investigated theoretically using a method of complex-coordinate rotation. Products of Slater orbitals are used to represent the two-electron wave functions, with ${\mathit{l}}_{\max }$=6 employed for the individual electron. Block matrices with up to ${\mathit{L}}_{\max }$=6 (I states) are used. Convergence behavior for the resonance parameters (resonance energy and width) is examined by using different values of ${\mathit{L}}_{\max }$. Results for the electric-field effects on the nearly degenerate ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$(1) and ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}^{\mathit{e}}$(2) states are given, as well as the effects on the nearby ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}^{\mathit{e}}$(1) state.

A principle for the efficient excitation of a three-level medium in a selective photoionization method is examined. It is shown that with special detunings for a given set of the laser-atom interaction the third-level population can be maximized. The expression of the optimal detunings is derived near the two-photon resonance region. It is shown that if the optimal detuning method is applied to three-level systems of Yb and Ca, the first-level populations are inverted to their corresponding third levels by about 100% and 86%, respectively. Application of this method to a Doppler-broadened medium is discussed and it is found that the optimal detuning method with counterpropagating waves will be very effective for selective ionization of wanted atoms.

The target gases ${\mathrm{H}}_2$, He, ${\mathrm{CH}}_4$, ${\mathrm{N}}_2$, Ne, and Ar were bombarded by 120-MeV ${\mathrm{Ne}}^{6+}$ ions to study the 2s-nl excitation from the metastable state 1${\mathit{s}}^2$2s2p ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$ of the ${\mathrm{Ne}}^{6+}$ projectile. The Coster-Kronig electrons from the transition 1${\mathit{s}}^2$2pnl (n≥7)–1${\mathit{s}}^2$2s+${\mathit{e}}^{\mathrm{-}}$ were measured using the method of zero-degree electron spectroscopy. It was found that the production cross section for the Coster-Kronig electrons is roughly proportional to the target atomic number. The experimental data are in agreement with impact-parameter calculations, which take into account the quenching of the ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$ metastable state of the projectile, by exciting or ionizing its 2p electron. This agreement supports the conclusion that the dielectronic two-center process is dominant in the production of Coster-Kronig electrons following the 2s-nl excitation of the projectile by ${\mathrm{H}}_2$ and He targets (>56%), and remains significant for the other investigated targets (>22%).

We describe a concept in the production of a highly polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ beam using multiple-electron capture and stripping collisions between a fast incident ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{2+}{}_{}{}^{}$ ion and a polarized alkali-metal atom at a strong magnetic field of 1–2 T. The yield and polarization of the outgoing ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ ion are calculated by solving the rate equations. The yield shows a characteristic pattern as a function of the alkali-metal-atom vapor thickness as a result of the multiple-electron capture and stripping collisions. The polarization shows a gradual decrease at low vapor thicknesses and a steep increase up to unity at about 2×${10}^{15}$ atoms/${\mathrm{cm}}^2$. By using 30-keV/amu ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ as a primary beam, a fully polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ beam of about 0.5 mA may be possible. It is also suggested that not only polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ ions but a polarized fast atomic ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ beam can be produced by the present method, where the expected polarization and beam intensity are ∼0.8 and ∼6×${10}^{15}$ atoms/sec, respectively.

A model complex optical potential (composed of static, exchange, polarization, and absorption terms) is employed to calculate the total (elastic and inelastic) electron-atom scattering cross sections from the corresponding atomic wave function at the Hartree-Fock level. The total cross sections for electron scattering by their corresponding molecules (${\mathrm{H}}_2$S, ${\mathrm{SiH}}_4$, ${\mathrm{CH}}_4$, ${\mathrm{CF}}_4$, ${\mathrm{CCl}}_4$, ${\mathrm{SF}}_6$, ${\mathrm{C}}_2$${\mathrm{H}}_4$, ${\mathrm{CCl}}_3$F, ${\mathrm{CClF}}_3$, and ${\mathrm{CCl}}_2$${\mathrm{F}}_2$) are obtained by the use of the additivity rule over an incident energy range of 10–1000 eV. The qualitative molecular results are compared with experimental data and other calculations wherever available; good agreement is obtained in intermediate- and high-energy regions.

We have applied the density-matrix formalism and a distorted-wave approximation scheme to calculate Stokes parameters, polarization fractions, alignment tensors, and orientation vectors for the ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{\mathrm{-}}{}_{}{}^{}$(v=0,1,2,3; N=1) states of ${\mathrm{H}}_2$, as well as rovibrationally resolved state-to-state differential and integral cross sections for the ${}_{}{}^1{}_{}{}^{}\mathrm{tsum}_{\mathrm{g}}^{+}{}_{}{}^{}$(v=0)→d ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{\mathrm{-}}{}_{}{}^{}$(v=0,1,2,3) excitation by electron impact at incident energies ranging from 15 to 40 eV. This is a systematic study for ${\mathrm{H}}_2$ of these quantities as a function of incident energy and final vibrational levels. Good agreement between our calculated Stokes parameters and the only available experimental data is observed. Our results show that these parameters are nearly independent of the vibrational quantum number of the excited state, that the polarization of the radiation emitted by the target in the subsequent decay process increases with increasing incident energies, and that the Stokes parameters are small compared with atomic values even if the fine and hyperfine structure effects are not taken into account.

Absolute total cross sections for the electron-impact single ionization of ${\mathrm{Mo}}^{4+}$ and ${\mathrm{Mo}}^{5+}$ ions have been measured using a crossed-beams technique from below the ground-state ionization threshold to 500 eV with typical total uncertainties of 9% near the peak of the cross sections. Molybdenum ion production in the source was facilitated by a mini-oven sublimating ${\mathrm{MoO}}_3$. The measured cross sections are in good agreement with distorted-wave calculations and are dominated by contributions from excitation autoionization. Nonzero cross sections below the threshold for ionization of ${\mathrm{Mo}}^{5+}$(4${\mathit{p}}^6$4d) ground-state ions indicate that metastable ions were present in the beam extracted from an electron-cyclotron-resonance ion source. No evidence of metastable ions was found in the case of the ${\mathrm{Mo}}^{4+}$ measurements. Ionization rate coefficients and fitting parameters are presented for the experimental data.

Photorecombination cross sections for highly charged uranium ions are calculated using many-body perturbation theory. The cross sections are resolved with regard to the final recombined level, corresponding to different x-ray light emitted during radiative stabilization of the dielectronic capture resonances. Interference between the radiative and dielectronic recombination processes is found to be more important for the weaker x-ray-resolved partial photorecombination cross sections than for the total cross sections.

Secondary-electron spectra of H-like ${\mathrm{Ne}}^{9+}$ ions incident with energies from 135 eV to 22.5 keV on an Al(111) surface were measured. The dependence of the K and L Auger electron yield on the energy of the projectile is studied. It is found for low impact energies that the angular distributions of the overall K Auger peak and the 740-eV component, which was formerly attributed to above-surface emission, show nearly the same anisotropy. Hence, the data provide evidence for K Auger emission from below the surface. Furthermore, for low projectile energies, it is found that, on average, two to three electrons are present in the L shell during the L and K Auger emission. For higher energies, the L shell is nearly empty during the L Auger emission, whereas five to six electrons are present in the L shell during the K Auger emission. Moreover, it is found that for higher energies the L Auger intensity is strongly reduced. These findings are attributed to the enhanced absorption of the L-shell electrons in the solid, as well as to a strong velocity dependence of the charge transfer directly into the Ne L shell.

The close relationship between the zero-point energy, the uncertainty relation, coherent states, squeezed states, and correlated states for one mode is investigated. This group theoretic perspective of the problem enables the parametrization and identification of their multimode generalization. A simple and efficient method of determining the canonical structure of the generalized correlated states is presented. Implication of canonical commutation relations for correlations are not exhausted by the Heisenberg uncertainty relation, not even by the Schrödinger-Robertson uncertainty inequality, but there are relations in the multimode case that are the generalization of the Schrödinger-Robertson relation.

Porous structure can strongly change the electric behavior of material submitted to bombardment by energetic electrons: strong electric fields (${10}^8$ V/m) can grow within the pores, because of the small sizes of these pores. We give a model of porous material that enables us to emphasize and illustrate the enhancement of the yield of secondary-electron emission (and the broadening in frequency of its profile) in a porous medium, compared to that in bulk material. Here we have considered materials of astrophysical interest [graphite, iron, aluminum (${\mathrm{Al}}_2$${\mathrm{O}}_3$), and silica]. The enhancement is characterized by two emission peaks for small energies of the primary electrons and by an increase of the yield roughly by a factor of 4 for large energies (>1 keV).

We calculate the mean energy loss of ${\mathrm{H}}_2^{+}$ molecular ions transmitted through carbon and aluminum foils as a function of the bombarding energy. Our results are in good agreement with available experimental data. Furthermore, inhomogeneities containing the foil are found to be essential in the energy-loss measurement of transmitted molecular ions.

Analytic expressions for a multiple-cascade model were derived to study the filling of L and K vacancies of hollow Ne atoms moving in shallow layers of an Al surface. The model requires cross sections for charge transfer into the L shell of the projectile that were determined from molecular-orbital calculations including screening effects of hollow atoms and asymptotic solid-state energies. The analysis accounts for mechanisms of Landau-Zener curve crossing and Fano-Lichten promotion. To describe the transport of the electrons within the solid, absorption and buildup effects were taken into account. The results from the cascade model show good agreement with angular distributions of Ne K Auger electrons recently measured. Attenuation effects were found to produce shifts in the K Auger spectra at varying observation angles. The significant difference previously observed for the mean L-shell occupation numbers during L and K Auger emission is explained by the present model.

Angle-resolved photoelectron spectra of gaseous ${\mathrm{C}}_{60}$ were recorded in the photon energy regions from 21 to 108 eV and from 295 to 320 eV. Partial cross sections σ and the angular distribution anisotropy parameter β vary significantly with photon energy, particularly in the near-threshold region of the valence and the core ionization regimes. Some of these effects may be attributed to scattering of the outgoing photoelectron by the atoms of the ionized ${\mathrm{C}}_{60}$ molecule. Our results indicate that the observed satellites of the C(1s) main line are most likely of shake-up character. Low-energy electrons emitted below the shake-off threshold indicate the occurrence of K-shell vacancy filling double Auger decay.

By means of adiabatically eliminating the upper level or levels of a Λ-configuration atom coupling to a two-mode quantized field, we have studied the influences of ac Stark shifts on the atomic coherent population trapping in two important atom-field coupling systems via nondegenerate Raman two-photon processes. The states of the field that trap the atom in its two nondegenerate lower levels are obtained, and the important roles of ac Stark shifts and properties of the atomic upper level or levels in the states of the trapping field in two Raman-coupling systems are also analyzed.

Though the interaction of a two-level atom with a field undergoing some arbitrary pattern of phase variation may be obtained by a numerical solution of the density-matrix equations, theory has proven to be problematic in providing a general, intuitive picture of the atom’s response to a phase-varying field. The convolution picture of the fluctuating field-atom interaction, known to spectroscopists for decades, is only valid in the regime of weak fields. Here we discuss a complementary intuitive view that is valid in the regime of strong, resonant fields. Specifically, when an atom’s response to a phase-varying field is considered in the instantaneous frame, the Bloch-vector trajectory always traces out a ‘‘figure-eight’’–type pattern, reminiscent of a Lissajous figure. This observation is demonstrated for a number of fields whose phase-varying patterns span a broad range (i.e., sinusoidal, two-frequency quasiperiodic, chaotic, stochastic), and analysis of the Bloch-vector equations then reveals the complete generality of this response. The analysis also reveals that the temporal variation of the atomic population to phase fluctuations in the strong, resonant field regime is nearly proportional to a simple product of the field’s phase and its first derivative.