We have investigated the spin-rotation interaction in the van der Waals molecule RbKr using molecular-beam magnetic-resonance techniques. The bound ${}_{}{}^2{}_{}{}^{}\Sigma$ molecules were produced in an expansion-cooled molecular beam and the interaction between the electronic spin angular momentum ($\hslash \overrightarrow{\mathrm{S}}$) of the rubidium valence electron and the rotational angular momentum ($\hslash \overrightarrow{\mathrm{N}}$) of the molecule was probed by magnetic resonance. A value for the strength of the interaction and a model of its dependence upon the internuclear separation were obtained. Results of numerical calculations of all bound and quasibound vibrational-rotational states of the RbKr ground-state potential are presented. These wave functions permit a detailed comparison of the results obtained by this technique and those obtained by M. Bouchiat et al. using optical-pumping techniques in a high-temperature gas cell. Excellent agreement is obtained when all of the relevant molecular states are considered.

The dominant formation and quenching processes in $E$-beam pumped ArF* and KrF* lasers are discussed. The quenching of ArF* by ${\mathrm{F}}_2$ and Ar has been measured by analyzing the ArF* ($B{}_{}{}^2{}_{}{}^{}\Sigma _{\frac{1}{2}}^{}{}_{}{}^{}\to X{}_{}{}^2{}_{}{}^{}\Sigma _{\frac{1}{2}}^{}{}_{}{}^{}$) fluorescence as a function of the ${\mathrm{F}}_2$ and Ar partial pressures. We have also measured the displacement of the Ar in ArF* by Kr to form KrF*. The dominant quenching processes of KrF* were identified, and the rate constants were measured. The ArF* and KrF* are formed from the ionic states with high efficiency. Interception of the precursors can be made negligible by choosing the experimental conditions properly. The quenching of KrF* by Ar and Kr is mainly a three-body process resulting in the formation of ${\mathrm{Kr}}_2$F*. The emission from ${\mathrm{Kr}}_2$F* was observed in a broadband centered at 410 nm. We have verified that the ${\mathrm{Kr}}_2$F* is produced subsequent to the KrF* formation by performing a laser saturation experiment.

The charge-changing cross sections ${\sigma }_{-0\mathrm{}}$ and ${\sigma }_{-+}$ have been measured for ${\mathrm{H}}^{-}$ ions incident on a Cs vapor target with energies in the range 30-200 keV. When the incident ion has an energy of 100 keV, ${\sigma }_{-0\mathrm{}}=1.80\mathrm{}\times {10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ and ${\sigma }_{-+}=1.30\mathrm{}\times {10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$. The cross sections ${\sigma }_{g+}$ and ${\sigma }_{g-}$ have been measured for fast H(ls) atoms incident on a Cs target with energies in the range 30-200 keV. When the incident atom has an energy of 100 keV, ${\sigma }_{g+}=5.58\mathrm{}\times {10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ and ${\sigma }_{g-}=3.75\mathrm{}\times {10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$. Also measured are the equilibrium fractions and the maximum neutral fraction when ${\mathrm{H}}^{-}$ is incident on a Cs vapor target with energy in the range 30-200 keV. The maximum neutral fraction when ${\mathrm{H}}^{-}$ is incident on Cs is 0.58 for energies in the range 100-200 keV.

I present a general treatment for evaluating the angular distribution of ejected electrons from doublet resonant states and their interference with direct ionization. The formulation is applied to sodium, and the results are found to agree very well with two sets of experimental data. It is also found that the direct ionization cross section for sodium is unusually low for secondaries of ∼25 eV, with a sharp peak at the angle predicted by the binary encounter approximation. The dependence of the incident and the secondary energies and other features of the process are discussed in detail.

We have measured the ratio of the cross section for $K$-electron capture to that for total $K$-vacancy production for 0.75-5-MeV protons on targets of ${\mathrm{O}}_2$, ${\mathrm{N}}_2$, and Ne. This was done by detecting Auger electrons from the target $K$-shell relaxation in coincidence with charge-neutralized projectiles. The fraction of $K$-shell vacancy production due to electron capture ranges from 0.028% to 3.3%, and the $K$-shell fraction of total electron capture from 2.5% to over 80%. By combining these data with previously measured (or calculated) cross sections for total $K$-vacancy production, we deduce cross sections for $K$-shell capture alone. The cross sections follow Oppenheimer-Brinkman-Kramers scaling laws for higher velocities, and are in fair absolute agreement with more complete charge-transfer calculations.

Cross sections for the production of excited hydrogen in the $3d$, $3s$, $4s$, and $5s$ states have been measured for 1- to 5-keV ${\mathrm{H}}^{-}$ ions incident upon He, Ar, Xe, and ${\mathrm{N}}_2$. The results show nominally flat cross sections which scale as a function of principal quantum number faster than $n^{-3\mathrm{}}$. Comparison is made with similar results for $\mathrm{np}$ states, and the implication that these results may have on some recently proposed collision models is discussed.

We construct a quantum ensemble to describe nonrelativistic three-particle scattering, and derive expressions for the observable scattering rates. These expressions are seen to reduce to the familiar expressions involving the modulus squared of the $T$ matrix, provided the final momenta are chosen to avoid the disconnected and double-scattering singularities. We show that our expressions remain finite in the neighborhood of the disconnected singularities, and that the predicted rates are consistent with the physical interpretation of the disconnected processes.

We evaluate the contributions of double-scattering singularities to three-particle scattering rates. It is shown that these contributions are finite and consistent with the physical interpretation of double-scattering processes. The "double-scattering regions" of momentum space where these processes contribute are calculated, and it is shown that in these regions the double-scattering contributions dominate and the regular part of the $T$ matrix can be neglected.

The $2s-2p$ transition in the lithiumlike ion ${\mathrm{C}}^{3+}$ is studied in the resonance region below the $n=3\mathrm{}$ threshold. A five-state close-coupling expansion is used. Cross sections are calculated using the $R$-matrix method for $\mathrm{O}\le L\le 4$ and the noniterative integral-equation method for $L>\mathrm{}4\mathrm{}$. A complicated structure of numerous, generally narrow, resonances is obtained for impact energies in the range 1.4-2.6 Ry. The resonances lead to a small overall enhancement of the average cross section.

$K$-shell ionization cross sections for Ho, Au, and U by proton impact have been measured over the incident energy range 1-4 MeV. The measured cross sections are larger than those predicted from the plane-wave Born, semiclassical, and binary-encounter approximations including Coulomb-deflection and binding-energy effects by factors from 2 to 20. However, it is shown that these large disagreements can be well explained by the semiclassical theory using relativistic wave functions for the $K$-shell electrons. The validity of various approximate estimations of electronic relativistic effects is discussed. Some results on ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-ion impact are also discussed. Ratios of x-ray production cross sections for $K{\alpha }_2$, $K{\beta }_1$, and $K{\beta }_2$ lines to that of $K{\alpha }_1$ line are shown as a function of proton energy and the results indicate little simultaneous ionization probability in the $L$, $M$, and $N$ shells of heavy atoms.

The conditions necessary to sustain rotational resonances in very low-energy electron scattering by molecular hydrogen are examined. Semiempirical interaction potentials are used in close-coupling calculations to obtain resonance energies, as eigenvalues of a projected Hamiltonian, and phase shifts and resonance widths from solutions for the total Hamiltonian. An unrealistic electron-molecule interaction potential is required in order to sustain a rotational resonance under single collision conditions. However, at high densities where average molecular separations are of the order of $15a_0$ to $30a_0$, resonance structure can be generated through a model potential which includes a modification due to neighboring molecules. Effects due to the presence of molecular dimers are also investigated.

Two approximations, motivated by heavy-particle scattering theory, are tested for weak-coupling electron-atom (ion) inelastic scattering theory. They consist of replacing the one-electron scattering orbitals by their Langer uniform approximations and the use of an average trajectory approximation which entirely avoids the necessity for generating continuum orbitals. Numerical tests for a dipole-allowed and a dipole-forbidden event, based on Coulomb-Born theory with exchange neglected, reveal the error trends. It is concluded that the uniform approximation gives a satisfactory prediction for traditional weak-coupling theories while the average approximation should be limited to collision energies exceeding at least twice the threshold energy. The accuracy for both approximations is higher for positive ions than for neutral targets. Partial-wave collision-strength data indicate that greater care should be exercised in using these approximations to predict quantities differential in the scattering angle. An application to the $2s{}_{}{}^2{}_{}{}^{}S-2p{}_{}{}^2{}_{}{}^{}P$ transition in Ne viii is presented.

We have investigated nonequilibrated neutral fractions in hydrogen beams transmitted through carbon foils bombarded with ${\mathrm{H}}^0$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$ projectiles having energies from 0.5 to 2.4 MeV/amu. Measurements with neutral projectiles provide a direct determination of the charge-exchange cross sections for fast protons in solids. The fact that the solid cross sections have been found close to the corresponding gas cross sections is discussed and confronted with existing theories. For very short dwell times the role played by projectile electrons in neutral-atom production is demonstrated, and it is shown that the approach to equilibrium follows essentially the same law for ${\mathrm{H}}^0$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$ projectiles. An overproduction of neutrals has also been observed with molecular ion projectiles for longer dwell times. An explanation of this effect is suggested in terms of a multistep process in which a target electron gets correlated with one proton before being captured by another proton of the cluster. Angular distributions of neutrals produced from incident molecular beams indicate the possible formation of a repulsive molecular state on emergence from the foil.

The destruction rates of the xenon $6s^{\prime }{\left[\frac{1}{2}\right]}_0$ metastable and $6s^{\prime }{\left[\frac{1}{2}\right]}_1$ resonance atoms by collisions with ground-state xenon atoms have been measured by studying the temporal dependence of the number densities of the $6s^{\prime }$ and $6p$ atoms. The studies have been made both during the earlier afterglow of a xenon pulsed discharge and after the selective production of the $6s^{\prime }{\left[\frac{1}{2}\right]}_{0,1}$ atoms by a laser excitation in the late afterglow. An original optical pumping technique, using a tunable pulsed dye laser, was employed to populate the $6s^{\prime }{\left[\frac{1}{2}\right]}_{0,1}$ levels by excitation of the $6s{\left[\frac{3}{2}\right]}_2$ long-lived metastable atoms to $6p^{\prime }$ levels. The pressure dependence of the decay frequencies of these $6s^{\prime }{\left[\frac{1}{2}\right]}_{0,1}$ atoms was analyzed in the xenon pressure range of 0.04 to 1 torr and a kinetic model describing the evolution of the densities of these atoms after their production was established. The rate coefficients for the relaxation of the $6s^{\prime }{\left[\frac{1}{2}\right]}_0$ metastable and $6s^{\prime }{\left[\frac{1}{2}\right]}_1$ resonance atoms by two-body collisions involving a ground-state xenon atom are (8.45±0.85) × ${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$ and (6.65 ± 1.00) × ${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$, respectively. Results show that, in fact, at least 75% of this relaxation is a transfer of population to the $6p{\left[\frac{1}{2}\right]}_1$ level following ${\mathrm{Xe}}^{*}\left(6\mathrm{}{s}^{\prime }{\left[\frac{1}{2}\right]}_{0,1}\right)+\mathrm{Xe}\rightleftarrows {\mathrm{Xe}}^{*}\left(6p{\left[\frac{1}{2}\right]}_1\right)+\mathrm{Xe}-\Delta E$. These collisional transfer processes have been explained by means of Mulliken's xenon molecular potential curves.

A significant perturbation in the energy distribution of electrons has been observed for collisions of ${\mathrm{H}}^{-}$ on ${\mathrm{N}}_2$. The spacings between the large oscillations in the 1- to 4-eV region of the ejected electron spectra have been measured at observation angles between 30° and 150° for impact of 35- to 10000-eV ${\mathrm{H}}^{-}$ on ${\mathrm{N}}_2$. A model is proposed which interprets these results in terms of the formation and decay of a series of vibrational autodetaching states of ${\mathrm{N}}_2^{-}$. Electron distributions calculated using a molecular model based on the Franck-Condon principle for the excitation of the ${\mathrm{N}}_2^{-}$ states and various possibilities for the decay are compared with the experimental results.

Cross sections for production of target-atom carbon $K$ x rays in thin evaporated carbon films are determined from spectra obtained using a double-focusing soft-x-ray spectrometer with calibrated transmission. A maximum value of 2.3 × ${10}^{-19\mathrm{}}$ ${\mathrm{cm}}^2$ is found for 18-MeV oxygen ions. A maximum ionization cross section of 4.8 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ is estimated from the data. Cross sections for x rays on both sides of the carbon $K$ edge are determined. Nitrogen ions produce more $L$-shell ionization at low energies than carbon or oxygen ions, both of which create very few $K{L}^2$ satellite x rays below about 9 MeV.

Charge exchange in ${\mathrm{He}}^{+}$ and ${\mathrm{Ar}}^{+}$ collisions with ${\mathrm{H}}_2$ (${\mathrm{D}}_2$) and ${\mathrm{N}}_2$ is studied at small angles. This work extends our earlier studies which primarily emphasized the direct inelastic scattering at low keV energies. Using time-of-flight techniques for energy analysis of the scattered atoms, it is directly shown, for the first time, that in ${\mathrm{Ar}}^{+}$ + ${\mathrm{H}}_2$, ${\mathrm{Ar}}^{+}$ + ${\mathrm{N}}_2$, and ${\mathrm{He}}^{+}$ + ${\mathrm{N}}_2$ the dominant small-angle charge-exchange process is quasiresonant ($Q\approx 0$). In ${\mathrm{He}}^{+}$ + ${\mathrm{H}}_2$ there is no available quasiresonant channel, and here the dominant final channels are associated with energy losses from 13 to 18 eV. A simple model is proposed.

Configuration interaction (CI) effects are examined for both initial and final states in the $L$- and $M$-shell Auger spectra of Cu and Zn. CI accounts for the anomalous energy splitting of ${}_{}{}^1{}_{}{}^{}D$ and ${}_{}{}^3{}_{}{}^{}P$ terms in the $L_{2,3}-M_{2,3}{M}_{2,3}$ Auger transition. At the same time CI increases the $L_{2,3}-M_1{M}_{4,5}$ ${}_{}{}^1{}_{}{}^{}D$ transition rate, so that the ${}_{}{}^1{}_{}{}^{}D$ intensity is comparable to the ${}_{}{}^3{}_{}{}^{}D$ intensity. CI effects on the ${}_{}{}^1{}_{}{}^{}D$ double-vacancy lifetimes, while in the right direction, are not sufficient to account for the observed difference in $L_3-M_1, M_{4,5}$ ${}_{}{}^1{}_{}{}^{}D$ and ${}_{}{}^3{}_{}{}^{}D$ linewidths. CI effects cannot account for the discrepancy between calculated and measured $M_1$ and $M_{2,3}$ linewidths. It is hypothesized that the discrepancy arises from the use of Herman-Skillman rather than Hartree-Fock wave functions in the calculation of low-energy super Coster-Kronig matrix elements. With matrix elements adjusted via this hypothesis the $M_1-VV$ and $M_{2,3}-VV$ Auger line shapes are calculated for Cu. Further the $L_3-M_{2,3}{M}_{2,3}$ and $L_3-M_{2,3}{M}_{4,5}$ line shapes, including final-state lifetime effects, are calculated. The latter calculations indicate that a discrepancy between calculated and measured $L_{2,3}-MM$ configuration intensities is an experimental artifact.

We have calculated the photoionization cross section for the $\left(1\mathrm{}{s}^{2}2s^{2}2p^{5}3s\right){}_{}{}^3{}_{}{}^{}P$ metastable state of neon using ab initio, many-electron wave functions in the $\mathrm{LS}$-coupling scheme. We have considered all the channels which arise from the $\left(1\mathrm{}{s}^{2}2s^{2}2p^5\right){}_{}{}^2{}_{}{}^{}P$ state of ${\mathrm{Ne}}^{+}$ and an ejected $p$ electron. The continuum was made discrete by approximating the final states as superpositions of square-integrable configurations. The Stieltjes moment-theory technique was used to construct the continuum oscillator strength distribution. Both the dipole-length and the dipole-velocity forms of the cross section were evaluated. We have examined systematically the effects of orbital relaxation, core polarization, and electron correlation and found them to be important within 5 eV of threshold. The peak value of the photoionization cross section for metastable Ne is 1.9 × ${10}^{-19\mathrm{}}$ ${\mathrm{cm}}^2$, which is much smaller than the corresponding value for the ground state. We have also calculated the line strengths for a few bound-bound transitions as well as the static polarizability of the ${}_{}{}^3{}_{}{}^{}P$ metastable state.

Theoretical considerations led to the prediction that the transition radiation following inner-shell photoionization has an angular dependence $I\left(\theta \right)\sim 1+\beta P_2\left(cos\theta \right)$. The asymmetry parameter $\beta$ was determined experimentally for the $L$-III transitions ($\mathrm{Ll}$ and $L\alpha$) of uranium. A comparison with the calculations of Scofield indicates that the measured asymmetry ($Ll=0.062\mathrm{}$) is 40% greater than predicted. Our experiment was not sensitive enough to detect asymmetry in the $L\alpha$ radiation.