The theory of molecular-orbital x-ray emission occurring during the primary vacancy-producing collision (the "one-collision spectrum") is developed. Calculations are presented for an illustrative excitation process (direct impact ionization in a symmetric collision system). It is shown that because of coherence of the excitation and radiative processes the resulting emission profile is very different from that expected if the events were incoherent (quasistatic model). In particular, the profile undergoes a strong red shift relative to the incoherent component and is relatively velocity independent in shape.

An extension of the Bethe theory for the total inelastic cross section in the Born approximation is presented and used to evaluate the total electron-loss cross section for ${\mathrm{H}}^{-}$ collisions on H and He targets at high energies. Sum rules are used to derive expressions for both the leading and the next leading order contributions to the asymptotic cross section. A comparison with the available experimental data for He targets shows good agreement with the theoretical calculation. In the case of hydrogen the calculated cross section for atomic H targets shows a clear preference for the larger values of the cross section obtained by several groups and disagrees with the conflicting lower experimental data from two other measurements. When corrections for ${\mathrm{H}}_2$ are included, this conclusion remains true for the conflicting experimental data near 10 MeV, but the calculated cross section in this case favors the lower experimental data near 1 MeV. Results are also presented for the total elastic cross section and the total nondetachment inelastic cross section. The latter is smaller than the total electron-loss cross section at intermediate energies, but exceeds it at sufficiently high energies. However, the convergence of the series generated in the Bethe theory approach for the nonloss cross section appears to be much slower than that of the electron-loss cross section.

Energy spectra of electrons ejected from autoionization states in helium by electron impact have been extensively measured for primary energies from 65 to 1000 eV and for ejection angles from 13° to 142°. The line shape in energy spectra undergoes a noticeable change with ejection angle as well as impact energy, reflecting the characteristics of the corresponding autoionization state. The single differential cross sections (differential in angle) for emissions of autoionized electrons have been obtained by integrating the energy spectra in the vicinity of each isolated resonance with respect to the energy after subtraction of the continuum background, for the $\left(2\mathrm{}{s}^2\right){}_{}{}^1{}_{}{}^{}S$, $\mathrm{}\left(2s2p\right)\mathrm{}{}_{}{}^3{}_{}{}^{}P$, $\left(2\mathrm{}{p}^2\right){}_{}{}^1{}_{}{}^{}D$, and $\mathrm{}\left(2s2p\right)\mathrm{}{}_{}{}^1{}_{}{}^{}P$ states as a function of primary energy at 33°, 127°, and 142°. Profiles of the spectra due to the $\left(2\mathrm{}{s}^2\right){}_{}{}^1{}_{}{}^{}S$ state have been analyzed using Fano's formula, and the shape parameter $q$ is given as a function of ejection angle for 250-eV impact. A number of the autoionization states lying above ∼62 eV have also been measured and identified as members of the $\mathrm{}\left(2sns\right)\mathrm{}{}_{}{}^1{}_{}{}^{}S$, $\mathrm{}\left(2pnp\right)\mathrm{}{}_{}{}^1{}_{}{}^{}S$, $\mathrm{}(\mathrm{sp}2n-)\mathrm{}{}_{}{}^3{}_{}{}^{}P$, $\mathrm{}\left(2pnp\right)\mathrm{}{}_{}{}^1{}_{}{}^{}D$, and $\mathrm{}(\mathrm{sp}2n+)\mathrm{}{}_{}{}^1{}_{}{}^{}P$ ($n=2-5\mathrm{}$) series, and our results are compared with previous results of theory and experiment.

Measurements of $K$ vacancies of F, S, and Cl ions penetrating various solids at MeV/amu energies indicate that the formation of those vacancies is well described by a simple model of competing $K$-shell rearrangement processes. Specifically, the progression at increasing penetration depth toward equilibrium vacancy fractions and the magnitudes of the fractions themselves find quantitative agreement in the model. The observation of substantial residual excitation in Cl and S at 2 MeV/amu implies that $K$ relaxation via Auger transitions is a significant post-foil charge-changing mechanism for those ions. Equilibrium effects previously taken to be due to dynamic screening by target electrons are herein attributed to the $K$ equilibrium process.

An electron-impact spectrometer is described which, by means of a modification, is able to observe energy and angular distributions of ion fragments produced by molecular dissociation processes with a good precision and sensitivity. ${\mathrm{O}}^{-}$ ion formation through dissociative electron capture in CO has been studied. An analysis of the observed ${\mathrm{O}}^{-}$ differential cross sections using the theory of O'Malley and Taylor and two partial waves indicates that the two reactions leading to ${\mathrm{O}}^{-}$ both proceed through a ${}_{}{}^2{}_{}{}^{}\Pi$ resonant state. Both resonances appear to have a ${\sigma }^2{\pi }^3{\pi }^2$ configuration by analogy with isoelectronic NO, and their parents would be the $a^{\prime }{}_{}{}^3{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$, for the process with a 9.62-eV threshold, and possibly the $d{}_{}{}^3{}_{}{}^{}\Delta$ state, for the process with an onset at 10.88 eV.

Electron impact excitation functions for the $\mathrm{Hg}\left(6\mathrm{}{}_{}{}^3{}_{}{}^{}P_{0,2}^{}{}_{}{}^{}\right)$ metastable states were measured from threshold to 8.5 eV. The $6{}_{}{}^3{}_{}{}^{}P_{0,2}^{}{}_{}{}^{}$ states were detected by monitoring the forbidden photon emission. The $6{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ state was also selectively detected by monitoring the 2537-Å emission from collisional deexcitation to the $6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state followed by radiative decay to $6{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$. Structure observed in the excitation functions appears to be due to autoionization of short-lived excited states of ${\mathrm{Hg}}^{-}$. The ratio of cross sections for formation of the $6{}_{}{}^3{}_{}{}^{}P_{2,0}^{}{}_{}{}^{}$ states, $\frac{{\sigma }_2}{{\sigma }_0}$, determined at the peak of the $6{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ excitation function ($E\simeq 5.8$ eV), is 9.1. The ratio of cross sections at the peak of each excitation function ($6{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$, $E\simeq 5.8$ eV; $6{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$, $E\simeq 5.2$ eV) is 5.2.

$K$-shell charge-transfer cross sections are calculated for swift fully stripped ions impinging on target atoms in a post-interaction distorted-wave formalism. The projectile interaction with the residual target atom is part of the unperturbed Hamiltonian, and is approximated by its asymptotic form while the consequent projectile distortion is approximated by an eikonal wave function. The results are compared to experiment and to other theoretical calculations and are used to shed light on some aspects of the three-body Coulombic rearrangement process and in particular on the significance of asymptotic properties of interactions and wave functions on the results of simple approximation schemes.

A molecular approach employing quantum close-coupling calculations has been utilized to calculate the cross sections for the reactions $\mathrm{Na}\left(n{}_{}{}^2{}_{}{}^{}D\right)+\mathrm{H}\mathrm{e},\mathrm{N}\mathrm{e},\mathrm{A}\mathrm{r}\to \mathrm{Na}\left(n{}_{}{}^2{}_{}{}^{}F\right)+\mathrm{H}\mathrm{e},\mathrm{N}\mathrm{e},\mathrm{A}\mathrm{r}$ for $4\le n\le 20$ at a collision energy of 0.04 eV. The calculations employ exact asymptotic coupling matrix elements and the recently measured term splittings for the $\mathrm{Na}(n{}_{}{}^2{}_{}{}^{}D-n{}_{}{}^2{}_{}{}^{}F)$ sequence. The cross sections are found to rise rapidly with increasing $n$ to a maximum cross section of the order ${10}^{-13\mathrm{}}$ ${\mathrm{cm}}^2$ at $n$ values of 7-12. For larger values of $n$, the cross sections decrease with increasing $n$. The magnitude of the maximum cross section is found to roughly correlate to the electron scattering length of the noble-gas perturbing atom. The theoretical calculations compare well with recent experimental measurements of Gallagher, Edelstein, and Hill.

The collision processes $A^{*}+B\to A+B^{+}+e^{-}$ (Penning ionization) and $A^{*}+B\to A{B}^{+}+e^{-}$ (associative ionization), where $A$ and $B$ are atoms, are considered in terms of the molecular-orbital (MO) correlation diagrams associated with the reactant and product channels. MO correlation diagrams are calculated for ${\mathrm{He}}^{*}\mathrm{}\left(1s2s\right)+\mathrm{Ar}\left(3\mathrm{}{p}^6\right)$ within the multiple-scattering $X\alpha$ one-electron self-consistent-field scheme for both spin-polarized and non-spin-polarized orbitals. The ionization process is discussed in terms of an Auger-type mechanism. By inspecting the MO's involved in the Auger-type process in their united-atoms limit, an analysis is made of the angular momentum contributions needed in describing the emitted electron in the body-fixed frame. A procedure is proposed for constructing MO correlation diagrams based on atomic-orbital energies at the separated- and united-atoms limits, which are determined from readily available data on ground-state energies of neutral atoms. Estimated MO correlation diagrams are presented for the four collision pairs ${\mathrm{He}}^{*}\mathrm{}\left(1s2s\right)+\mathrm{Ar}\left(3\mathrm{}{p}^6\right)$, $+\mathrm{Kr}\left(4\mathrm{}{p}^6\right)$, $+\mathrm{Hg}\left(6\mathrm{}{s}^2\right)$, and ${\mathrm{Ne}}^{*}\left(2\mathrm{}{p}^{5}3s\right)+\mathrm{Ar}\left(3\mathrm{}{p}^6\right)$, and in each case an analysis is made of the angular momentum components of the emitted electron in the body-fixed frame. The results confirm that relatively few $l$ values need be included in describing the emitted electron. Our analyses show that it is important to use spin-polarized MO's to obtain detailed behaviors at pseudocrossings, and that the effect of Born-Oppenheimer rotational coupling must be considered, particularly between MO's that converge to the same united-atoms limit.

The $2s_{\frac{1}{2}}\to 2p_{\frac{1}{2}}+\mathrm{one}\mathrm{photon}$ transition rate is calculated and discussed for hydrogen and hydrogenlike ions. It is noted that the induced transition rather than the spontaneous transition is of primary importance since it is the basis of many of the precision Lamb-shift measurements. The lack of a calculation of the transition rate other than a heuristic nonrelativistic derivation which requires a nontrivial assumption motivates the calculation presented here based on the external field approximation to quantum electrodynamics. It is found that the heuristic answer is correct in lowest order. In this derivation we see that the $2s_{\frac{1}{2}}\to 2p_{\frac{1}{2}}+\mathrm{one}\mathrm{photon}$ transition gives an apparent contradiction to the often-stated remark that for the electric dipole matrix element there exist three equivalent representations, the "length," "velocity," and "acceleration" forms. The difficulties of an experimental determination of this transition rate using induced transitions in hydrogenlike ions are briefly noted as well as the somewhat different case of heavy muonic atoms where the spontaneous $2s_{\frac{1}{2}}\to 2p_{\frac{1}{2}}+\mathrm{one}\mathrm{photon}$ transition has been observed.

The shapes of the thallium (Tl) 535- and 377.6-nm resonance lines broadened by 500-1500 Torr of noble gases have been measured at 743 K. The reported normalized emission intensities yield absorption coefficients in absolute units for all portions of the line. The shift and broadening of the Lorentzian-shaped line cores, the wavelengths of the transition to non-Lorentzian wings, wing shapes, and satellite positions, shapes, and intensities are reported. As an example, a pair of excited and ground-state interaction potentials are given for the Xe case to explain the shift, width, and intensities in all portions of the line wings.

A multiconfiguration Hartree-Fock calculation is used to test the hypothesis that ground-state correlations involving excitation of a single of electrons from an outer $p$ shell into $d$ orbitals are the dominant ones in the photoionization cross sections of Ne, Ar, Kr, and Xe. Dramatic improvement in the agreement of dipole length and dipole velocity forms of the cross section is obtaining in going from a Hartree-Fock to a multiconfiguration Hartree-Fock calculation. Results are found to be comparable to recent values obtained using the random-phase approximation with exchange and the $R$ matrix.

Calculations have been performed for the photoionization of the Ne $2p$, Ar $3p$, Kr $4p$, and Xe $5p$ isoelectronic sequences using both multiconfiguration Hartree-Fock and Hartree-Slater wave functions. The results show that away from the vicinity of a Cooper minimum, which moves rapidly into the discrete in going along an isoelectronic sequence, agreement between the two calculations is quite good. Thus we conclude that for highly stripped ions, the Hartree-Slater results are an excellent approximation to the multiconfiguration Hartree-Fock photoionization cross sections.

Stark shift of Bii $\lambda 3451$ Å due to plasma microfields was measured in a luminous shock tube. Line profiles, photographically recorded in second order, were compared to closeby wavelength fiduciaries from lowpressure rare-gas lamps. Electron densities [(3-16)×${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$] for each exposure were found by fitting ${\mathrm{H}}_{\beta }$ profiles to theoretical line shapes. Results, estimated reliable to 25-30%, are compared with theoretical predictions.

We report further accurate measurements of fine structure in $D$, $F$, and $G$ Rydberg states of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ obtained using a microwave-optical resonance method and electron-bombardment excitation. Single-quantum electricdipole transitions $10{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-10\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}F_3^{}{}_{}{}^{}$, $11{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-11\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}F_3^{}{}_{}{}^{}$, $12{}_{}{}^3{}_{}{}^{}D_J^{}{}_{}{}^{}-12\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}F_{J^{\prime }}^{}{}_{}{}^{}$, and $6{}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}-6\mathrm{}{}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}$, and two-quantum transitions $7{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-7\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}G_4^{}{}_{}{}^{}$, $9{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-9\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}G_4^{}{}_{}{}^{}$, $10{}_{}{}^3{}_{}{}^{}D_J^{}{}_{}{}^{}-10\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}G_{J^{\prime }}^{}{}_{}{}^{}$, and $16{}_{}{}^1{}_{}{}^{}P-16\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}F_3^{}{}_{}{}^{}$ were observed. Both electrostatic and relativistic fine-structure intervals were determined with uncertainties less than 1 MHz and are compared with theoretical results. The data constitute the first measurements of $G$-state fine structure in helium. Series formulas incorporating all our measurements are given for serveral resonance series, and we show that the entire series $n{}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}-n{}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}$ can be predicted to within 75 ppm.

The problem of resonance fluorescence from a two-level atom that is driven near resonance by a laser beam of finite bandwidth is tackled via the Heisenberg equations of motion, by a simple generalization of our previous treatment. It is found that the two-time intensity correlation function is again factorizable into a product of the mean light intensities at the two times, each of which is slightly modified under broad-band excitation from its value under monochromatic excitation. The spectrum of the fluorescence is affected rather more drastically, and, in general, becomes asymmetric under broad-band excitation.

X-ray line spectra were collected from exploded (Al to U) wire plasmas produced by ${10}^{12}$-W pulse discharges of high-energy electrons in the Gamble II generator. High-ionization states were found in these spectra that provided new spectroscopic data. The Ne- and Ni-like isoelectronic sequences involving $L$- and $M$-shell transitions were extended to high-atomic-number elements, Ag and Au, respectively. The correlation of spectra and x-ray pinhole images revealed that the high-temperature emission emanates from small (< 75 μm), high-density pinched regions with plasma temperatures of 1-2 keV (based on the coronal model). Other x-ray emission arises from cool-plasma (50-200 eV) regions associated with the flaring structure as seen in x-ray-pinhole images. In addition to low-temperature thermal x-ray emission from the flare regions, energetic electrons produce nonthermal inner-shell spectral lines. As the atomic number increases, the relative intensity of the cool plasma to high-temperature thermal emission increases systematically for isoelectronic sequences involving $K$-, $L$-, and $M$-shell transitions. The plasma characteristics determined from the distribution of ionization states in the exploded-wire spectra correlate well with those from other high-energy-density generating devices, namely the vacuum spark and plasma focus.

We present a semiclassical solution for a Zeeman-split, optically pumped, spin-½ system interacting with a strong radio-frequency field. The method of solution presented here is based upon a matrix continued-fraction expansion, and can explain any resonance phenomena which occur for arbitrary geometrical configurations of the pumping beam or the rf field polarization axis. Theoretical predictions of line shapes for some cases are reported and discussed. The solution can also explain some deviations of the observed Bloch-Siegert shift at high rf power from the behavior predicted by a previous semiclassical theory, which can account for simple geometrical configurations only.

We present a theoretical analysis of an experiment on near-resonant three-photon ionization of Cs. We have calculated all parameters entering in the equations for the density matrix and have shown that previously invoked higher-order laser-induced Stark shifts are negligible. A complete solution of the equations suggests that the observed unusual dependence of the ion signal on laser intensity is the result of spatial beam effects.

The behavior of a ring laser rotating with nonuniform angular velocity has become of interest, both experimental and theoretical. Within a framework of modest idealizations, we present a classical, relativistically exact theoretical analysis. The beat frequency, we find, is given by an expression of the Sagnac form but with the instantaneous angular velocity in place of the usual constant velocity. One has an "instantaneous Sagnac effect."