An approach to the calculation of the impulsive (e,2e) cross section, which extends the plane-wave-impulse approximation to include the long-range tails of the Coulomb interaction in the final state, is presented. The model divides the collision space into two regions: an inner sphere where short-range forces are active and responsible for the impulsive character of the collision, and an outer region where the tails of the Coulomb interactions act on the charged free particles, which can be treated in a semiclassical way. An extensive comparison between the predictions of this model and experimental data relative to atomic hydrogen and helium, as derived from the literature, is presented. The model constitutes an improvement over previous impulsive models, mainly for the angular distributions of (e,2e) events.

δ-electron emission from superheavy quasiatomic systems formed during heavy-ion collisions was studied for several systems with united atomic charge $Z_u$ up to 171. The double differential cross sections $d^2$σ/${\mathrm{dE}}_e$d${\Omega }_e$ including the cross sections for total electron emission, electron emission from 1$s_{1/2}$ and 2$p_{1/2}$σ states of the quasiatom, and the electron emission probabilities P($R_0$) for total electrons as well as for K-shell electrons are presented. These results are compared with available theoretical results. The results are interpreted in terms of the relativistic localization of the electronic wave functions and the effects due to the increase of the electronic binding energy. Binding-energy differences between K- and L-shell electrons are given for all the systems studied.

We propose an algebraic-eikonal approach to electron-molecule scattering. In this approach the coupling to both rotational and vibrational molecular states is taken into account simultaneously and to all orders in the coupling strength. We present closed analytic expressions for the transition matrix elements for the two dynamical symmetries of the vibron model for diatomic molecules, the U(3) and O(4) limits. It is shown that the large-N limit of the O(4) result corresponds to the rigid-rotor case. The extension to triatomic and polyatomic molecules is straightforward.

We have measured the angular and energy distribution of the absolute cross sections for ejection of electrons from water vapor by electrons incident at 50–2000 eV. The angular range was 15° to 150° and the range of secondary electron energies was from 2 eV to an energy equal to the primary energy minus the first ionization potential. Electron energies were analyzed with a parallel-plate electrostatic analyzer with a resolution of 1.1%. Generally good agreement is obtained with the data of Opal et al. [J. Chem. Phys. 55, 4100 (1971)] at 500 eV except at the extremes of their angular range. Our energy distributions are compared to various binary-encounter-model calculations.

Absolute values of cross sections for electron ejection by protons of 15–150 keV energy have been measured as a function of the angle and energy of the electrons. The range of angles was 10° to 160° and the electron energy range was 1–300 eV. The doubly differential cross sections were also integrated over energy or angle to obtain singly differential and total cross sections and also average ejected electron energies. Good agreement is obtained with Senger’s DDCS-MT (doubly differential cross section–mixed treatment) theoretical treatment using the Salin factor.

Absolute values of cross sections for electron production in collisions of neutral hydrogen atoms of 20–150 keV energy with water vapor molecules have been measured as a function of the ejection energy and angle. The range of angles was 10° to 160° and the electron energy range was 1–300 eV. The doubly differential cross sections were integrated over angle and/or energy to obtain singly differential cross sections, total electron production cross sections, and average energies of ejection. The angular distribution of the electron loss peak was found to have some features in common with the cross section for elastic scattering of electrons.

Theoretical calculations of the stopping power of the electron gas for slow ions, v<$v_F$, are reviewed. New results are presented for stopping power and effective charge based on nonlinear density-functional calculations. Extensive comparisons with available experimental data show that these new theoretical results are clearly superior to earlier calculations based on linear theory.

In the Fock-Tani representation for rearrangement collisions, the interaction Hamiltonian decomposes into terms representing interactions within each arrangement channel and channel-changing rearrangement interactions. The two-potential formalism is used to cast transition amplitudes into a distorted-wave form in which in-channel interactions are treated exactly and interchannel transitions in finite order, thus separating initial- and final-state interactions from rearrangements. Self-energies arising from infinite-order summations of selected interchannel transitions are also considered and illustrated by shifts and broadenings of scattering and reaction resonances.

The energy systematics of single and double K-shell-vacancy production in titanium have been investigated near the limit of zero target thickness for incident chlorine ions over an energy range of 7–15 MeV/amu. Single and double K-shell-vacancy production cross sections have been measured for projectiles incident with zero, one, and two initial K-shell vacancies. Single and double K-shell-to-K-shell electron-transfer cross sections have been obtained indirectly using differencing procedures based on the projectile-charge-state dependence of single and double K-shell-vacancy production. The measured cross sections have been compared to theoretical models for direct ionization and inner-shell electron transfer. Together with previously reported data, these cross sections also have been used to investigate the relative importance of these mechanisms for K-shell-vacancy production in heavy-ion–atom collisions over a range of scaled velocities of 0.24≤$V_1$/$V_{2K}$≤1.29.

A set of indices {σ,τ,ζ,η} is introduced to replace the four orbital quantum numbers that occur in cross-section formulas. Each index belongs to a different species of a $C_{2v}$ point group; only σ ranges to infinity whereas all four orbital l’s do. Results of an earlier calculation are restructured in terms of {σ,τ,ζ,η} affording an improved interpretation of those results. Directions of further investigation are indicated.

We examine collision-induced electronic transitions mediated via long-range electrostatic fields such as those generated by ions and molecular dipoles. The chief characteristics of such processes are the relatively narrow widths and intense strengths of the collision-induced spectral lines. These features arise from and reflect the long-range nature of electrostatic forces which tend to generate long-lived collision-induced transition electric dipole moments. Of particular interest is the prediction that the collision-induced electromagnetic rates are proportional to the Raman cross section of the normally forbidden transition.

The depolarized interaction-induced light scattering spectra of liquid argon have been measured, along the coexistence curve, at four different temperatures in the range 84.1–110.7 K. The experimental spectral moments have been evaluated, on an absolute scale, by means of a calibration procedure which makes use of a solution, in liquid argon, of about 1.4% hydrogen, whose rotational Raman lines are used as an intensity standard. The reproducibility of the calibration technique is very good and the present measurement fully confirms a previous experiment [D. Varshneya et al., Phys. Rev. A 23, 77 (1981)]. Molecular-dynamics computer simulation has been used to evaluate the first two even spectral moments in similar thermodynamic conditions. We used the pairwise additive potential of Barker, Fisher, and Watts and a model of the pair polarizability anisotropy which was derived from the low-density-gas collisional spectrum at room temperature. The overall agreement is good even if some refinements seem necessary. Since the effect of irreducible triple-dipole terms of both polarizability and potential is found to be smaller than the present experimental uncertainty, the small observed inconsistencies between measurement and computer simulation might be attributable to minor defects of the pair functions. More experimental data taken at different temperatures would help in refining the models.

For potential scattering, with ${\delta }_L$(k) the phase shift modulo π for an incident wave number k, Levinson’s theorem gives ${\delta }_L$(0)-${\delta }_L$(∞) in terms of $N_L$, the number of bound states of angular momentum L, for ${\delta }_L$(k) assumed to be a continuous function of k. $N_L$ also determines the number of nodes of the zero-energy wave function $u_L$(r). A knowledge of the nodal structure and of the absolute value of ${\delta }_L$(0) is very useful in theoretical studies of low-energy potential scattering. Two preliminary attempts, one formal and one ‘‘physical,’’ are made to extend the above results to single-channel scattering by a compound system initially in its ground state. The nodal structure will be of greater interest to us here than an extension of Levinson’s theorem.

The formal approach is applied to $e^{+}$-H and $e^{+}$-He scattering. Both H and He have zero orbital angular momentum and a nodeless ground-state wave function ${\psi }_T$. An effective one-body wave function $u_L$ for the positron incident with zero kinetic energy can be constructed by factoring out the spin and Euler-angle dependence of the full scattering wave function Ψ and projecting the remaining ‘‘radial’’ function $R_L$ onto ${\psi }_T$.

The nodal surfaces of $R_L$ are shown to divide configuration space into at most $N_L$+1 subdomains, where $N_L$ is the number of composite bound states of the given L. Since $N_L$=0 for $e^{+}$-H and $e^{+}$-He, it follows that $u_L$ is nodeless and that ${\delta }_L$(0)=0, for all L. Partial but useful information on the nodal structure of Ψ for $e^{\mathrm{-}}$-H scattering is also deduced. Interestingly, nodal surfaces exist which are not consistent with a naive generalization of (bound-state) one-dimensional Sturm-Liouville theory.

The physical arguments, based on the qualitative concept of an effective central potential seen by each target particle and by the incident particle P, strengthen a previous surmise on the value of ${\delta }_{\mathrm{LJ}}$(0) for $e^{\pm }$-atom scattering and for the scattering of neutrons or protons by a heavy nucleus; L and J are the quantum numbers of the incident P, and ${\psi }_T$ is assumed to have zero spin and zero orbital angular momentum, but ${\psi }_T$ need not be nodeless, and P need not be distinguishable. Roughly, the surmise is that ${\delta }_{\mathrm{LJ}}$(0)=$K_{\mathrm{LJ}}$π, where, for the given L and J, $K_{\mathrm{LJ}}$ is the number of composite bound states plus the number of one-particle states excluded by the Pauli principle.

The effective R-matrix model and the R-matrix propagative method applied earlier to elec- tron–diatomic-molecule scattering are extended to treat dissociative attachment of collinear triatomic molecules. To describe the vibrational excitation and dissociative attachment of ${\mathrm{CO}}_2$ in the 4-eV region, the nuclear dynamics is solved on a Wall-Porter potential-energy surface. A hybrid approach is developed in which the $L^2$ and R-matrix propagation methods are combined to evaluate the global R matrix. Our calculations show that it is easier to excite the symmetric mode vibrations than the asymmetric mode vibrations. Our results also show that the observed structures in the energy dependence of the dissociative attachment cross sections are due to the vibrational states of the negative ion (${\mathrm{CO}}_2$${\mathrm{}}^{\mathrm{-}}$) and not to the vibrational states of the CO fragment.

Krypton L-MM Auger spectra have been measured with good resolution and statistics and have been compared with relativistic calculations in intermediate coupling with configuration interaction. Good agreement between experiment and theory is found; the effects of final-state configuration interaction, ground-state correlation, and Coster-Kronig fluctuation shifts are found to be significant. A previously reported anomaly in the $L_2$-$M_2$,3${\mathrm{M}}_4$,5 spectrum may be due to a phase error in earlier calculations.

We have measured the infrared photodetachment cross section of the negative molecular ion ${\mathrm{NO}}^{\mathrm{-}}$ for photons in the range 3000–4150 ${\mathrm{cm}}^{\mathrm{-}1}$ (0.372–0.514 eV), using a coaxial ion-beam–laser-beam apparatus. The cross section declined by 56% as the photon energy increased. There was no evidence for an expected threshold in the cross section near 4000 ${\mathrm{cm}}^{\mathrm{-}1}$ from the channel NO(v’=2)←${\mathrm{NO}}^{\mathrm{-}}$(v’’=0). This surprising result awaits theoretical interpretation.

Lead and uranium K x-ray spectra recorded with a specially designed Ge detector have been fitted using an accurately determined line-shape model. This provides the first accurate Ge measurements of the K${\alpha }_3$ relative intensity and the first reported measurement of the ${\mathrm{KM}}_1$ relative intensity. Measurements of the transition probabilities of K${\beta }_1$ and K${\beta }_2$ relative to the K${\alpha }_1$ line provide a much more stringent test of calculated overlap and exchange effects than earlier ratios of gross line groups.

Dielectronic recombination coefficients for ground-state ions of the He isoelectronic sequence have been calculated for 13 ions, with atomic number 6≤Z≤42, in the isolated resonance approximation, for temperatures in the range 0.1≤T≤12 keV. The detailed Auger and radiative rates of the doubly excited states were evaluated by using the multiconfiguration Dirac-Fock model. The behavior of the dielectronic recombination coefficient along the isoelectronic sequence is examined. The effect of relativity drastically alters the dielectronic satellite structure of He-like ${\mathrm{Fe}}^{24+}$ and ${\mathrm{Mo}}^{40+}$. However, the relativistic effect reduces the total dielectronic coefficients for ${\mathrm{Fe}}^{24+}$ by only 10% and 2.5% at T=0.5 and 5 keV, and for ${\mathrm{Mo}}^{40+}$ by 18% and 5% at T=2 and 5 keV, respectively.

The two major proposed first-order test theories for special relativity are shown to be equivalent. The results of many experimental tests of special relativity are given in terms of the free parameters of this unified test theory.

We studied the autoionization electrons of two doubly excited states of helium—(2s2p${)}^1$P and (2$p^2$${)}^1$D—that were collisionally excited by multiply charged and relatively fast ions. The ion velocities (2–4.5 a.u.) were faster than the velocities of the emitted electrons (∼1.6 a.u.). The wings of the measured autoionization profiles were significantly different from standard Beutler-Fano profiles. These differences are largest at forward angles, smaller ion velocities, and larger ion charges. The distortion is explained with use of a classical kinematic model. After emission, the autoionization electron is accelerated if emitted in a forward direction (toward the projectile) or slowed down if emitted in a backward direction (away from the projectile). A modification of a post-collision interaction theory accounts for the interference between the bound-state electrons and the continuum electrons. Fits of the measured electron-energy spectra with use of this model show very good agreement.