Experimental $\mathrm{Al}\mathrm{}\left(K\right)\mathrm{}$ x-ray production cross sections are reported for atomic oxygen projectiles incident on solid aluminum targets with kinetic energy $E$ in the range $0.15\le E\le 91$ MeV from which Al $K$-shell ionization cross sections are deduced for the projectile energy range $1\le E\le 91$ MeV. For $E\lesssim 1$ MeV nearly all observed x rays are caused by the recoiling aluminum atoms. The results are compared with theories of Coulomb ionization to the target continuum. Differences between experiment and these theories are examined with respect to contributions to inner-shell ionization from electon capture and Pauli excitation. It is found that Coulomb ionization is the dominant process for projectile velocities ${\nu }_1>4\mathrm{}$ a.u., while Pauli excitation dominates when ${\nu }_1<4\mathrm{}$ a.u. Electron-capture processes are significant at high energies, but are negligible for ${\nu }_1<4\mathrm{}$ a.u. for this projectile target system.

Low-energy, collisional excitation of neutral helium in He-${\mathrm{He}}^{+}$ collisions is investigated using the potential-energy curves for the molecular ions. Ground and excited states of the ${}_{}{}^2{}_{}{}^{}\Sigma _g^{}{}_{}{}^{+}$, ${}_{}{}^2{}_{}{}^{}\Sigma _u^{}{}_{}{}^{+}$, ${}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$, and ${}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ states are calculated using an ab initio configuration-interaction method for the $n=2\mathrm{}$ neutral excitations of helium. A threshold of 23.5 eV is determined for the ${}_{}{}^1{}_{}{}^{}S$-$2{}_{}{}^3{}_{}{}^{}S$ excitation. Thresholds for the ${}_{}{}^1{}_{}{}^{}S$-$2{}_{}{}^1{}_{}{}^{}S$-$2{}_{}{}^3{}_{}{}^{}P$ and $2{}_{}{}^1{}_{}{}^{}P$ states are also estimated from the potential-energy curves. $\Sigma$-$\Pi$ interactions are also considered to explain the photon polarization reported in the $2{}_{}{}^1{}_{}{}^{}P$ excitation cross section. The ${}_{}{}^2{}_{}{}^{}\Sigma _g^{}{}_{}{}^{+}$ spectrum of potential-energy curves appears to dominate the $\Sigma$-$\Sigma$ radial interactions, while the ${}_{}{}^2{}_{}{}^{}\Sigma _u^{}{}_{}{}^{+}$ and ${}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ states are apparently necessary to explain the $2{}_{}{}^1{}_{}{}^{}P$ cross section.

Recent results due to Kelsey for certain high-momentum-transfer collisions are generalized to all such processes. A simple model for scattering in this region is presented which provides considerable insight into these processes. The model predicts that all processes in the regions where first Born terms fail are proportional to the nuclear Rutherford-like scattering, and gives a simple formula for calculating the cross section in terms of electronic form factors.

An exact closed form expression for the Glauber-Bonham-Ochkur exchange amplitudes for electron-hydrogen scattering is derived. The results are applied to the elastic scattering from the ground state of the hydrogen atom, where a closed-form expression was also derived for the total exchange cross section. Investigation of the inclusion of exchange in the differential cross section for total electron scattering is also presented. It is shown that exchange effects are quite important and that their inclusion, rather than the inclusion of angle effect or the inclusion of the full eikonal effects, does tend to make the Glauber prediction in much better agreement with the experiment.

We clarify the computational procedure used in a stabilization calculation of the resonance energy. We propose a new, variational method for the calculation of the resonance width for elastic scattering. The method is based on a minimum principle for the width which holds for $L^2$ trial functions satisfying certain assumptions. The method gives all the resonance parameters, including the background phase shift, without requiring traditional scattering calculations.

The theory of radiative Penning ionization is developed. The continuum radiation emitted is related to the photoionization cross section of the quenching atom.

The foundations for an independent-electron model for charge-state distributions of heavy elements having passed through solids, as well as for beam-foil populations, are presented and discussed. It is proposed that the fraction $P_i$ of particles with charge $\mathrm{ie}$, $e$ being the charge of the proton, is given by the simple expression $P_i=\left[\frac{n!}{i!(n-i)!}\right]{\alpha }^{n-i}{(1-\alpha )}^i$, where $n$ is the number of electrons possible outside a closed core, and $\alpha$ is a parameter accounting for outer electrons. Modification of this expression in case the core becomes ionized is discussed. The model and its implications are compared to experimental data, and good agreement is generally found.

An approximate quasiclassical treatment is presented for calculating the cross sections for charge transfer from a neutral alkali-metal atom colliding with a halogen atom (chlorine or fluorine). The electron is treated by the time-dependent perturbation in the two-state approximation. The two states are the ground (or the first-excited) state of alkali-metal atom and the ground state of the halogen negative ion. Charge-transfer cross sections are calculated as a function of relative velocity ($v$) of collision between $v=0.01\mathrm{} \mathrm{and} 5$ a.u. Qualitative features of these cross sections are compared with an earlier work on alkali-metal-oxygen collisions. An asymptotic formula at low velocities of collision $v\to 0$ is obtained, which compares with the earlier formula obtained by Bates. At higher velocities cross sections are found to vary as $\frac{1}{v^2}$, as in the Born approximation.

Computations have been made of the electron-impact ionization cross sections of multicharged ions of C, O, N, Ne, and Ar in the binary-encounter approximation. For ions of the four lighter species, the dominant ionization mechanism is that of direct electron ejection to the continuum. For Ar, excitation of inner-shell electrons to unoccupied bound levels with subsequent autoionization can also make a significant contribution to the total ionization process for some ions. The calculated binary-encounter values are in reasonable agreement with recent experimental data and with the quantum-mechanical calculations of Trefftz for ${\mathrm{O}}^{+4\mathrm{}}$ and ${\mathrm{O}}^{+5\mathrm{}}$.

Cross sections for $K$-vacancy production by 4.88-GeV protons on elements between Ni and U have been measured. These cross sections lie approximately a factor of 1.4 to 2.5 above the plane-wave Born-approximation predictions. To partially explain these deviations, we argue that an additional contribution due to the interaction between the currents of the projectile and target electrom must be added to these theories.

The summation of all the higher-order contributions to multiphoton absorption in atoms is presented. The nonperturbative expressions for the transition amplitudes are expressed in terms of continued fractions. They account for the whole perturbation originated by the radiation field on the atom but do not exhibit explicit expression for the level shift. In the case of radiation fields of high intensity the only reliable determination of the level shift involves a careful location of the poles of the resolvent operator. The theory has been tested in considering a two-level atom. An extremely rapid convergence of the continued fractions has been observed, and accurate results concerning high-order resonance shifts have been obtained. The expressions for the transition amplitudes being nonperturbative with regard to the field strength, they can be considered as analytic continuations of the perturbation series. This provides a useful approach to the problem of ultraintense fields.

Time-resolved measurements were made of the shifts of the ionized helium lines at 1640 Å ($n=3\mathrm{}\to 2$) and 1215 Å ($n=4\mathrm{}\to 2$), and of the Stark profile of the $\lambda 1215$-Å line. An electromagnetic shock tube was used as a light source. The plasma conditions corresponded to electron temperatures of ∼3 eV and electron densities of ∼2× ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$. No significant shifts were found for the $\lambda 1640$-Å line. The $\lambda 1215$-Å line underwent a red shift of ≲ 0.5 Å, consistent with semiclassical estimates of plasma polarization shifts. The measured Stark width of the $\lambda 1215$-Å line was 10-45% greater than the calculated width based on the measured width of the $\lambda 4686$-Å line.

Core- and valence-electron spectra of the $n$-alkanes have been recorded under high resolution in the gas phase. The measured core-level binding energies decrease with an increasing number of carbon atoms in the molecules. The whole shift ranges over 0.6 eV. These small shifts are ruled by the relaxation energy and are discussed with the aid of various theoretical models. It is found that the transition-potential model together with CNDO/2 (complete neglect of differential overlap) calculations describes satisfactorily the variation of the core-level binding energies. The shakeup spectra of methane, ethane, and propane are presented and tentatively interpreted. The valence-electron structures of methane, ethane, propane, $n$-butane, and $n$-pentane are studied. Results are correlated with ab initio calculations using an extended basis set. The formation of a valence-electron band is discussed. For instance, it appears that $n$-tridecane provides a convenient finite model for the band structure of an infinite linear polymer.

The hyperfine constants, isotopic level shifts, and a pressure self-broadening constant of the $7{}_{}{}^2{}_{}{}^{}P$ states of ${}_{}{}^{203,205}{}_{}{}^{}\mathrm{Tl}$ have been measured by the Doppler-free two-photon absorption technique. The hyperfine constant of the $7{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state is found to be greater than that of the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state. This anomaly is tentatively attributed to a sign change in the promoted core $S$-electron spin-polarization contribution to the hfs as calculated by Fermi and Segrè for the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state. The isotope shift of the $7{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ state is 20% smaller than that of the $7{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state, confirming the nuclear volume effect of the $p_{\frac{1}{2}}$ electron. At higher pressures line broadening is observed as the Tl density is increased.

The multichannel $J$-matrix technique is used to solve the pseudostate close-coupling equations for ${\mathrm{H}}^{-}$ photodetachment using only $L^2$ basis functions and standard configuration-interaction techniques. The problem of linear dependence which arises when the same $L^2$ basis is used to expand both the target and free electrons is discussed and exactly solved using a matrix partitioning. Results for total and partial photodetachment cross sections are given from threshold to 70-eV photon energy (1664 to 18 nm) with emphasis on the single-photon two-electron ejection cross section, and the ${}_{}{}^1{}_{}{}^{}P$ shape resonance just above the hydrogenic $n=2$ threshold.

Using the Heisenberg operator approach, we have calculated the emission rate of a multilevel atom whose transitions involve both upper- and lower-state splittings. The emission rate is first calculated by a frequently used power-flow expression and is shown to exhibit lower-state beats. This power-flow expression requires care in its interpretation because it does not account for the measurement process. We then derive an alternative, detection-oriented emission rate and show that lower-state beats are not observable in a photodetection experiment.

Deactivation rates of the $n=3$ states of the triplet system of helium by collisions with ground-state helium atoms have been measured by time-resolved selective excitation spectroscopy with a short-pulse dye laser as a function of gas temperature from 300 to 600°K. Results are in generally good agreement with predictions of the multistate curve-crossing model for scattering recently proposed by J. S. Cohen; they bring complementary information on the relevant intermolecular potential and on coupling between states.

$\frac{K\beta }{K\alpha }$ measurements for Ti, V, Cr, Fe, Cu, and Zn have been performed for cases of $K$ vacancies created by $K$-electron capture and x rays. For nuclei with $Z<\mathrm{}28\mathrm{}$ a marked difference in the $\frac{K\beta }{K\alpha }$ ratios obtained by the two modes has been found.

A procedure is used which combines the truncated diagnoalization method with the open-channel close-coupling approximation in the calculation of widths of autoionization states in two-electron systems. The method is capable of systematically and efficiently calculating the widths for all two-electron systems. Calculations are made for ${}_{}{}^1{}_{}{}^{}P_{}^0{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}P_{}^0{}_{}{}^{}$ helium, and ${}_{}{}^1{}_{}{}^{}P_{}^0{}_{}{}^{}$ hydrogen below the $N=2\mathrm{}$ threshold. In particular, it is found that the lowest member of the third series [classified as $(2,3\mathrm{}c)$)] has a width of 4.61 × ${10}^{-7\mathrm{}}$ eV, four times smaller than any previous calculation. It is also shown that the (+)-(-) classification used by many authors is inadequate to describe these states. Detailed comparison is made with the three- and six-state close-coupling and other calculations.

The waveguide propagation of a microwave magnetic field pulse at electron paramagnetic resonance (EPR) with a free radical sample of electron spins distributed along the guide displays the phenomenon of self-induced transparency (SIT). Predictions of plane-wave optical SIT are modified by summation of the magnetic-moment-microwave-field coupling over the transverse waveguide mode for specific sample geometries. Mode modified pulse area theorems are presented. Observed output pulse areas and shapes are compared with computer predictions. After pulse propagation over several absorption lengths a spontaneous zero-area pulse propagation effect is observed for a short weak input pulse with spectral width comparable to or larger than the spin-resonance linewidth. Alternating 180° phase shifts in the pulse carrier wave, accounting for zero area, signify magnetic dipole transitions which alternate between coherent absorption and emission to some extent, and therefore anomalous pulse propagation is observed. For pulses applied off-resonance, linear and nonlinear shifts of the average carrier frequency occur toward the center of the spin resonance.