Approximate cross sections for charge transfer between $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ and fully stripped carbon and nitrogen ions have been obtained in the velocity range 6 × ${10}^6$-7 × ${10}^7$ cm/sec. In these systems, transfer takes place into high-lying orbitals of the final-state ion. The Landau-Zener theory modified for application to a multistate system is used to calculate the cross sections. The coupling-matrix elements are determined both from a study of the pseudocrossings observed in the relevant system of the adiabatic potential curves and by direct calculation using the appropriate asymptotic parabolic wave functions. The resulting cross sections are large, in the ${10}^{-14\mathrm{}}$-${\mathrm{cm}}^2$ range for both ${\mathrm{C}}^{+6\mathrm{}}$ and ${\mathrm{N}}^{+7\mathrm{}}$, and show the relatively flat energy dependence characteristic of systems with a number of contributing curve crossings.

Cross sections for the inner-shell ionization of argon ions by high-energy electron impact are estimated. An improved form of the single-particle model with varying degrees of ionization is used in the calculation of the excitation amplitudes. Partial sums over the allowed final states are carried out using the semiclassical projection operator. This operator depends on a spectral cutoff parameter $e_b$, and a method for its determination is examined for the case of hydrogenic transitions. The ionization cross section incorporates both the direct excitation to the continuum and the Auger emission following the inner-shell excitations. For electron energies in the KeV range and for atomic targets with the core charges $Z_C$ less than 20, the direct ionization dominates, with the excitation Auger-emission mode making a small but appreciable contribution. The ionization cross sections for the neutral neon, and oxygen targets are also estimated.

High-resolution measurements have been made of Ti $K\alpha$ x rays and satellites ($K{L}^n,n=0\mathrm{}-4$) following bombardment of thick Ti targets by ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{n+}$, ${\mathrm{Li}}^{n+}$, ${\mathrm{C}}^{n+}$, and ${\mathrm{O}}^{n+}$ ions at energies of 1-5 MeV/amu. A systematic study was made of the effect of projectile atomic number $Z_1$ and energy $E_1$ upon the relative intensities, centroid energies, and widths of the various x-ray peaks. The intensity of the satellite structure relative to the diagram lines ($K{\alpha }_1,{\alpha }_2$) increases with increasing $Z_1$ for the same-velocity projectile up to $Z_1=8\mathrm{}$. Both the $Z_1$ and $E_1$ dependence of these intensities agree reasonably well with a theoretical model described elsewhere. Deviations of peak intensities from theory are discussed. Centroid energies of the peaks increase approximately linearly with $Z_1$ at a rate of ∼1 eV/Z. These energy shifts are compared with Hartree-Fock calculations of the x-ray energies for various members of $M$-shell ($3s \mathrm{and} 3p$) electronic vacancies. Peak widths range from 10 to 37 eV, increasing monotonically with $Z_1$ for most peaks and increasing monotonically with $n$ for all projectiles. No variation of centroid positions or peak widths was observed for different values of $E_1$ and fixed $Z_1$. The observed energy shifts and peak-width variations are discussed in terms of ionization of the $M$ shell, varying distributions of $L$-shell vacancies among the $2s$ and $2p$ subshells, and possible multiplet splittings.

$K$-shell x-ray production corss sections for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions on thin targets of Ni, Rb, Ag, and Sb were measured over the incident-ion energy range of 0.4-2.4 MeV/amu. Comparisons to theoretical predictions of the binary-encounter, semiclassical, and plane-wave Born approximations (PWBA) show that these theories overpredict the magnitude of the measured cross sections. The PWBA calculations with perturbation corrections for binding energy and Coulomb deflection effects included are in better agreement with the measured data for $\frac{E}{M}<1.2\mathrm{}$ MeV/amu. Comparison of the data to the perturbed PWBA calculations which also include corrections of electron polarization effects in the case of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ on Ni gives good agreement between these theoretical estimates and the measured $K$-shell x-ray production cross sections.

We measured total relative differential cross sections for electron collisions with molecular nitrogen. Results are presented between 6°-80° with 500-eV electrons and 2°-90° with 1-keV electrons. Theoretical calculations were also done utilizing partial waves for elastic channel and the Born approximation for the total inelastic cross section. In both cases use was made of Hartree-Fock-Clementi wave functions. The agreement between our theoretical and experimental results is analyzed, demonstrating the possibility of determining molecular-structure parameters at 1 keV.

We have measured the Ne $K$-shell electron spectra from a Ne gas target bombarded by 0.5-10 MeV ${\mathrm{H}}^{+}$ and 14-21 MeV N, 24-35 MeV O, 3-35 MeV F, and 40 and 50 MeV Cl in various incident ionic charge states. The F $K$-shell Auger-electron spectra have been measured for F-ion collisions with Ne gas from 3 to 15 MeV. Auger-electron production cross sections are deduced. ${\mathrm{H}}^{+}$ induced Ne $K$-shell Auger-electron production cross sections are compared to various theoretical Coulomb ionization predictions. The heavy-ion-induced Ne $K$-shell Auger-electron production cross sections increase with increasing projectile charge state at constant projectile energy. The F and Ne $K$-shell Auger-electron production cross sections from 3 to 15 MeV are favorably compared to calculations based on the molecular-orbital model.

Reported measurements by Broude et al. of the lifetime of the 3.34-MeV nuclear state in ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$, determined by Doppler-shift measurements on the $\gamma$ decay of the excited nucleus as it is slowed down by various absorbers, show an oscillatory structure that can be attributed to oscillations in the electronic stopping cross section ($S_e$) of the absorbers. Unlike previously observed oscillations in $S_e$, which were for channeled or forward-scattered particles, these are oscillations in the average value of $S_e$. We have considered the problem in terms of an extension of the Lindhard-Scharff-Winther (LSW) theory to low-velocity heavy ions. We find that in the LSW formalism the appropriate effective charge for the projectile is not simply related to conventional equilibrium charge distributions, for velocities corresponding to those in the nuclear lifetime measurements. Despite this, it is possible to obtain relative stopping powers, at a given velocity, which are strongly correlated with the apparent oscillations in the value of the nuclear lifetime.

The positron-hydrogen collision problem has been investigated using an integral form of the close-coupling approximation for a wider range of energies. The present formalism takes care of the rearrangement channel. The effects of the excited states of both the hydrogen and positronium atoms have been neglected. The elastic and the positronium-formation cross sections have been obtained explicitly in the energy region 0-200 eV. Because the integral form was used, the two-state results are reliable. The present results differ from the first Born results even at 200 eV.

Many-body perturbation theory is used to calculate the photoionization cross sections of the $2p$ and $2s$ subshells of the ${}_{}{}^3{}_{}{}^{}P$ ground state of neutral carbon. Resonances due to the $1s^{2}2s2\mathrm{}{p}^{2}np$ autoionizing configurations and two-electron resonances from the $1s^{2}2s^{2}3s3\mathrm{}p$ and $1s^{2}2s^{2}3p3\mathrm{}d$ configurations were calculated. Detailed agreement is obtained with the experimental data of Esteva, Mehlman-Balloffet, and Romand.

Collision-broadening theory is used to obtain a general expression for the steady-state rate of two-photon simultaneous absorption as a function of their sum energies and momenta in gases, under conditions where both homogeneous (collision) and inhomogeneous (Doppler) broadening take place. Effects of molecular motion on the line-broadening parameters are discussed, as well as extensions to bands of overlapping lines, inclusion of radiative damping, saturation effects, effect of intermediate resonating levels (consecutive absorption), and time-resolved experiments.

It is shown that the angular distribution of photoelectrons ejected on absorption of left or right circularly polarized light by a mixture of randomly oriented dextrorotatory and levorotatory optical isomers behaves as $A\pm Bcos\theta +C{cos}^2\theta$, where $\theta$ is the angle between the photoelectron momentum and photon direction of incidence and $\pm Bcos\theta$ is introduced by the presence of unequal numbers of each isomer. All coefficients of ${cos}^n\theta$ are of order $\alpha$, and analysis shows that $B$ can be as large as $A$ and $C$.

We report the first absolute measurement of the cross section for photoionization from a selectively excited short-lived atomic singlet state. Employing two simultaneous tunable laser pulses, the $3s3\mathrm{}p{}_{}{}^1{}_{}{}^{}P_1^o{}_{}{}^{}-3p^2{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ autoionization resonance in MgI was found to have a peak cross section of (8±4)×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at $\lambda 300.9$ nm and a half-width of 2.5 nm. The measured ratio of the cross sections to the $3p^2{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ states was 14:1. The effect of polarization of the lasers has been investigated and shown to provide a means of identifying the angular momentum states of autoionizing levels.

Precision measurements of the refractivities of ${\mathrm{H}}_2$, He, ${\mathrm{O}}_2$, CO, and Kr were made in the wavelength range 168-288 nm. By using a 1.2-m-long test cell and by keeping the test gas at accurately determined conditions near atmospheric pressure and room temperature, we were able to achieve accuracies (90% confidence limit) for the absolute refractivities that ranged from ±0.1% to ±1.0% depending upon the gas and wavelength range. For a given gas, the ratio of refractivities at any two wavelengths has a smaller uncertainty. For ${\mathrm{H}}_2$, CO, and ${\mathrm{O}}_2$, our results are for wavelengths shorter than those of previous measurements and, for He and Kr, our uncertainties are less than those of other measurements. For He our refractivities agree with the theoretical ones, but in the case of ${\mathrm{H}}_2$ our results are about 1% larger than the theoretical values. At the upper end of the wavelength range studied, our data are in agreement with previous measurements on ${\mathrm{H}}_2$, CO, and Kr. For ${\mathrm{O}}_2$ our results indicate that the hitherto available data are too large by amounts ranging from 0.8% to 10%.

X-ray photoelectron and Auger spectra involving $N_1$, $N_2$, and $N_3$ vacancy states of Pd, Ag, Cd, In, and Sn were measured and compared with results of free-atom calculations. As previously observed in Cu and Zn Auger spectra that involve $3d$-band electrons, we now also find free-atom characteristics, with regard to widths and structure, in the Ag and Cd $M_4-N_{4,5}{N}_{4,5}$ and $M_5-N_{4,5}{N}_{4,5}$ Auger spectra that arise from transitions of $4d$-band electrons. Theoretical $N_1$ widths computed with calculated free-atom Auger energies agree well with measurements. Theory, however, predicts wider $N_2$ than $N_3$ vacancy states (as observed for Xe), while the measured $N_2$ and $N_3$ widths are nearly equal to each other and to the average of the calculated $N_2$ and $N_3$ widths. The calculations are made difficult by the exceedingly short lifetime of some $4p$ vacancies and by the extreme sensitivity of super-Coster-Kronig rates, which dominate the deexcitation to the transition energy and to the fine details of the atomic potential.

When a small volume of atoms within a larger one is excited by a short pulse of electrons or light, the apparent lifetime of the decaying atoms is increased by the resonance trapping in the surrounding gas. In this paper the apparent lifetime is calculated for two different geometries and line shapes, and the result of having more than one lower level is presented.

Microwave transitions from the $d$ to the $f$ orbital levels have been observed in sodium with principal quantum number $n$ from 11 to 17 by detecting optical radiation from the $f$ levels, yielding precise values for the difference in the $d$ and $f$ quantum defects as well as the $d$ and $f$ fine-structure splittings. We found the $f$ doublets to be normal, reversed from the $d$ doublets, which are known to be inverted.

The Stark effect of the $N=1\mathrm{}$ rotational level in the metastable $c{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ electronic state of orthohydrogen has been measured using the molecular-beam magnetic-resonance method. The Stark-shift coefficients of orthohydrogen, unlike those of parahydrogen, are strongly dependent on static magnetic field strength. The measured magnetic field dependence of these coefficients agrees with a calculation in which we assume that the major contribution to this phenomenon is the mixing of hyperfine levels by the Zeeman-effect perturbation. The extrapolated zero-magnetic-field values of the Stark-shift coefficients are in reasonable agreement with the corresponding theoretical values. The Stark effect of the $N=2\mathrm{}$ rotational level of parahydrogen has been remeasured with considerable reduction in the experimental uncertainties. This allows a more meaningful comparison with theory. At large magnetic field strengths (100-150 G) the Stark effect of para-${\mathrm{H}}_2$ exhibits a small dependence on magnetic field which is due to mixing of the fine-structure levels by the Zeeman-effect perturbation.

It is shown that over an appreciable energy range $K$-, $L$-, and $M$-shell photoeffect total cross sections are proportional to $E1\mathrm{}$ internal-conversion coefficients from the same subshell. In the nonrelativistic dipole approximation the ratio $\frac{{\beta }^{E1\mathrm{}}}{\sigma }=\left(\frac{3}{8\pi }\right){\left(Z\alpha \right)}^{-2\mathrm{}}$, independent of shell and subshell; numerically, for $s$ waves, this ratio holds to 1 MeV. Screening effects enter only at low energies, reaching several percent at the $K$-shell threshold.

The photoionization cross sections and the oscillator strengths for helium, lithium, and beryllium atoms are calculated in the framework of the random-phase approximation with exchange. The energy-level shift for discrete transitions is taken into account consistently in this approximation. The results are compared with other many-body calculations and with the experimental data. The comparison shows that the random-phase approximation with exchange can even be used for systems with a small number of particles.

The correlation-state spectrum accompanying $1s$ photoemission in atomic neon was calculated by several methods, using the sudden approximation and focusing on states that are approximately described by single-electron excitation of the form $2p\to np$. All the calculations gave satisfactory energy values, but the predicted intensities differed widely. Multiconfiguration Hartree-Fock (MCHF) orbitals and orthogonalized MCHF orbitals gave intensities in poor agreement with experiment. A final-state configuration-interaction calculation gave accurate energies for seven $2p\to np$ correlation states, but when combined with a single-determinant initial state, yielded intensities low by about a factor of 2. Initial-state configuration interaction (ISCI), including double-electron excitation of the form $2p^6\to 2p^{4}n{p}^2$, etc., brought the intensities of the $2p^5\mathrm{np}$-type states into agreement with experiment. It was thus shown that ISCI is of equal importance to final-state CI in determining correlation-peak intensities. Correlation-state (or "shakeup") spectra therefore contain unique information about electron correlation in the ground state.