Absolute cross sections for electron detachment and charge transfer (or dissociative charge transfer) have been measured for collisions of ${\mathrm{H}}^{-}$ and ${\mathrm{D}}^{-}$ ions with ${\mathrm{N}}_2$, CO, ${\mathrm{O}}_2$, C${\mathrm{O}}_2$, and C${\mathrm{H}}_4$. The relative collision energies investigated range from a few eV up to several hundred eV. Electron detachment is found to be the dominant process for all the molecular targets except ${\mathrm{O}}_2$ for which charge transfer dominates. Isotope effects are observed in all the cross sections. Isotopic substitution reveals that the detachment cross sections scale with relative collision energy at low collision energies and with relative collision velocity at high collision energies. The general features of the charge-transfer cross section for the ${\mathrm{O}}_2$ target are in agreement with the ideas of a simple two-state collision model. The cross sections for charge transfer (or dissociative charge transfer) are found to be small for all targets except ${\mathrm{O}}_2$.

The collisional angular-momentum mixing of the $\mathrm{Na}\mathrm{nd}$ Rydberg states into states of higher angular momentum with Xe as the collisional partner has been studied in zero field and in the presence of a small electric field. The collisional $l$-mixing cross section in zero field has been measured for $9\le n\le 23$ using a vapor-cell-fluorescence method and a crossed-beam technique with a selective-field-ionization (SFI) scheme as the state detector. Using the $\left|m_l\right|$ selectivity of the SFI, we have also investigated the final-$\left|m_l\right|$-state distribution of the collisionally populated states of $l>\mathrm{}2\mathrm{}$. Our measurements suggest that the collisionally populated states have predominantly low $\left|m_l\right|$ values ($\left|m_l\right|\le 2$). An application of a low electric field (∼ 50 V/cm) substantially reduces the collisional population of the low-$\left|m_l\right|$ states, thus reducing the total cross section as well.

Total (elastic and inelastic) differential scattering cross sections for 40-keV electrons incident on helium have been measured with a precision of 0.1%. Theoretical scattering intensities as given by an explicitly correlated wave function are compared with experimental results. It is shown that corrections to the Morse expression for kinematic effects, at small angles, are adequate to relate scattering intensities at constant angle to incoherent x-ray scattering factors.

The emergence-angle dependence of energy loss of 7-MeV protons in Cu foils, the thicknesses of which are 3.743 and 7.576 mg/${\mathrm{cm}}^2$, has been measured with very high angular resolution. It was found that in both cases the energy loss increases as the emergence angle increases. The amount of the increase of the energy loss depends strongly on the thickness of the sample foils. Computer simulation was performed in order to investigate the origin of this phenomenon. Individual collision which protons undergo within the target was found to be restricted by the determination of detection angles. Considering properly the dependence of energy loss on impact parameter, we have obtained a good reproduction of the experimental results.

Polarization fractions for the $3{}_{}{}^1{}_{}{}^{}P\to 2{}_{}{}^1{}_{}{}^{}S$, $3{}_{}{}^1{}_{}{}^{}D\to 2{}_{}{}^1{}_{}{}^{}P$, and $4{}_{}{}^1{}_{}{}^{}D\to 2{}_{}{}^1{}_{}{}^{}P$ transitions of He excited by 15-keV to 120-keV ${\mathrm{H}}^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$ projectiles have been measured. The prominent structure in the polarization fraction for the $3{}_{}{}^1{}_{}{}^{}P$ transition was verified and previous experimental discrepancies were resolved. It is suggested that backcoupling to the projectile ground state is the physical mechanism producing the structure—a suggestion which awaits theoretical verification.

Electron-capture cross sections are reported for the reaction ${\mathrm{O}}^{8+}+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}\to {\mathrm{O}}^{7+}\mathrm{}(n,l)+{\mathrm{H}}^{+}$, with $n=4,5,6\mathrm{}$ and $l=0\mathrm{}$ through $n-1\mathrm{}$. The cross section for $n=7\mathrm{}$ is also estimated. The energy range extends from 13 eV/amu to 34 keV/amu. A Landau-Zener formula is given for use at lower energies. The calculations are quite analogous to those carried out for ${\mathrm{C}}^{6+}-\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ collisions in Phys. Rev. A 25, 1364 (1982), The modified perturbed-stationary-state calculation features the use of a mixed representation of diabatic and adiabatic states and the use of translation factors determined by Euler-Lagrange optimization within the mixed representation of states. One internuclear separation-dependent factor is used for the initial state, which correlates to ${\mathrm{O}}^{8+}+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$. A second factor is used for all the ${\mathrm{O}}^{7+}$+${\mathrm{H}}^{+}$ correlating states. Riley's semiclassical average approximation is used at low energies and the straight-line impact-parameter method is used at high energies. For the purpose of comparison, some calculations are also carried out by the method of Bates and McCarroll and by that of Piacentini and Salin. The approximation of neglecting $\pi$-$\pi$ and $\Delta$-$\Delta$ couplings is tested. The results are compared with those of other researchers.

In order to enable the measurement of nuclear structure effects on the emission of x rays following ($\alpha ,xn$) reactions, thin samples of Pb isotopes have been irradiated with $\alpha$ particles in 2-MeV steps between 30 and 110 MeV. X-ray excitation-yield curves have been measured on ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, and ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Pb}$ and show large variations with energy and the presence of maxima and minima. For each separated target isotope it is observed that the cross-section maxima and minima are correlated with the formation of a residual nucleus with odd and even neutron numbers, respectively. This effect is attributed to the level density in the residual nucleus which affects the transition energies and the conversion coefficients. In the case of ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ the nuclear cross sections are available and it is then possible to calculate the average number ${\overline{n}}_K$ of $K$ ionizations per nuclear reaction; this parameter is found to increase with bombarding energy as it is also correlated with the neutron number. These results clearly show that the x-ray emission yield is strongly dependent on the neutron number of the residual nucleus.

With the use of reference and distorted transition operators, a time-correlation-function representation of the inelastic differential cross section has recently been used to obtain distorted eikonal cross sections. These cross sections involve straight-line and reference classical translational trajectories that are unaffected by any internal-state changes which have occurred during the collision. This distorted eikonal theory is now extended to include effects of internal-state changes on the translational motion. In particular, a different classical trajectory is associated with each pair of internal states. Expressions for these inelastic cross sections are obtained in terms of time-ordered cosine and sine memory functions using the Zwanzig-Feshbach projection-operator method. Explicit formulas are obtained in the time-disordered perturbation approximation.

The hyperfine structure of the singlet and triplet $\mathrm{nd}$ Rydberg states ($n=12-17\mathrm{}$) in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been studied by Doppler-free ultraviolet-infrared double-resonance laser spectroscopy. Using the frequency-doubled output of a cw dye ring laser we have populated the $1s5p{}_{}{}^3{}_{}{}^{}P$ state of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ by excitation from the metastable $1s2s{}_{}{}^3{}_{}{}^{}S$ state at 294.5 nm. In a second step, an infrared single-mode cw color center laser is used to excite $d$ Rydberg states. The experimental results for the $n{}_{}{}^{1,3}{}_{}{}^{}D$ hyperfine splittings ($n=12-17\mathrm{}$) are in excellent agreement with semiempirical calculations using hydrogenlike wave functions. Anomalous isotopic shifts in the electrostatic energy intervals of 5 to 20 MHz were found for the states $n=12-17\mathrm{}$. These shifts are smaller than the shifts of about 35 MHz found for the states $n=5-8\mathrm{}$ with the help of anticrossing spectroscopy. No satisfactory explanation of these shifts has yet been found.

The most precise determination of the magnetic moments of the electron and positron come from the University of Washington $g-2\mathrm{}$ experiments. A small distortion in the magnetic field is introduced in these experiments so as to provide a mechanism to flip and measure the spin. The experiments would be substantially improved if this inhomogeneous part of the magnetic field were removed. Driving the end caps produces an electric field at the frequency ${\omega }_d$ which is parallel to the magnetic field. The cyclotron motion of the electron at frequency ${\omega }_c$ transforms this electric field into a magnetic field which is perpendicular to the main magnetic field and which alternates at frequency ${\omega }_c+{\omega }_d$ in the particle's rest frame. One might think that such an alternating magnetic field would flip the spin, thereby removing the need for the field inhomogeneity. There are, however, subtle relativistic corrections to the spin motion. These nearly cancel the motional magnetic field effect and rule out this scheme of spin flipping.

In this paper, we present the theory of photoelectron angular distributions in resonant multiphoton ionization that rigorously takes into account the saturation, ac Stark-shift, and the laser-linewidth effects. The influence of these effects on the distribution is incorporated through the coupling equations between the angle-resolved ionization probabilities and the (time-dependent) bound-state density-matrix elements. General expressions for the angular distributions are derived and several properties of these distributions are arrived at from these expressions. Finally, numerical results are presented to illustrate the effects of saturation, of ac Stark shifts, and of the laser line shape.

Microwave-optical polarization spectroscopy allowed the study of transitions between low-lying rotational states in the ${}_{}{}^2{}_{}{}^{}\Sigma$ ground state of CaCl which conventional microwave absorption and microwave-optical double-resonance (MODR) techniques would have failed to detect. In the $N=1\mathrm{}\leftarrow 0$ transition the hyperfine structure could be completely resolved. Linewidths obtained with the new method were between 1 and 2 MHz, an improvement of an order of magnitude compared to MODR.

A theory is developed of the ionization of inner-shell electrons during $\beta$ decay. For allowed transitions it is shown that in the lowest order of the coupling constants the transition amplitude for the process is a sum of two terms, one of which attributes the ionization process to the sudden change in nuclear charge, and the other to a virtual scattering of an inner-shell electron by the emerging $\beta$ particle. For the $K$-shell specific calculations are carried out using nonrelativistic hydrogenic wave functions and a Coulomb Green's function due to Glauber and Martin. Results whose relative accuracy is of order $Z\alpha$ are obtained for energy spectra, angular correlation functions, and the total internal ionization probability; numerical results are presented for the nuclides ${}_{}{}^{63}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{107}{}_{}{}^{}\mathrm{Pd}$, and ${}_{}{}^{151}{}_{}{}^{}\mathrm{Sm}$. The role of the virtual-scattering mechanism is assessed and a comparison with other recent theoretical work is made.

Anticrossing induced by the motional Stark effect created by atoms moving perpendicular to a strong magnetic field have been observed in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. These anticrossings couple the $n{}_{}{}^1{}_{}{}^{}P$ state with the nominal $n{}_{}{}^1{}_{}{}^{}D$, $n{}_{}{}^1{}_{}{}^{}F$, $n{}_{}{}^3{}_{}{}^{}F$, and $n{}_{}{}^{1,3}{}_{}{}^{}\mathrm{H}$ states via first-order (for the ${}_{}{}^1{}_{}{}^{}D$) and second-order Stark effects. The theory is derived to explain the line shape in the second-order case. This theory, along with the previously existing first-order-effect line-shape theory, is used to obtain the zero-velocity crossing points. These values are used in a leastsquares fit to determine the zero-field intervals. The $n{}_{}{}^1{}_{}{}^{}P-{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ interval is determined precisely for $n=6, 7, \mathrm{and} 8$ and the $n{}_{}{}^1{}_{}{}^{}G-n{H}_{\mathrm{av}}$ interval is determined for $n=6\mathrm{} \mathrm{and} 7$. A power-series expansion establishes the $n{}_{}{}^1{}_{}{}^{}P$ energy levels with respect to the higher $\mathrm{nL}$ states with high precision.

Examining the dynamics of a degenerate two-level system excited by coherent resonant light, we exhibit a transformation of basis states which reduces the problem to a set of independent nondegenerate one- and two-state systems. More generally, reduction of multilevel Hamiltonians requires only that the states can be collected into two sets; within each set the states are degenerate, unlinked by Hamiltonian matrix elements. The remaining Hamiltonian linkages must share the same time dependence, but are otherwise arbitrary. We apply this method to reduction of the angular momentum degeneracy of a two-level atom excited by elliptically polarized light and to multiple-laser resonant excitation of multiple levels into a common level.

Resonant-saturation spectroscopy has been carried out in both the $V$ configuration and the inverted-$V$ configuration in fast, accelerated atom beams of Ne I* and Ca I*. Hole (peak) creation in the velocity distributions are shown to yield resonances Doppler free to first order in a collinear geometry, which allows high spectral stability and resolution. Wave numbers for three optical transitions in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ are reported.

Complete Raman spectra of transparent media are obtained with a single 10-nsec, 10-mJ, laser pulse by a new spectroscopic technique which exploits resonant behavior of nondegenerate four-wave mixing in the phase-conjugate geometry.

Threshold-region measurements are reported for the production of single-vacancy and multiple-vacancy configurations of atomic argon by monochromatic x-ray photons in the region of the $1s$ ionization threshold. The experiment used monochromatized synchrotron radiation produced in the six-pole wiggler at the Stanford Synchrotron Radiation Laboratory with 3.2-GeV electrons at circulating currents of 20-30 mA. Secondary radiation including elastically and inelastically scattered radiation as well as fluorescent spectra were analyzed in a focusing spectrometer with a linear position-sensitive detector. Fluorescent spectra in the $K\beta$ region were modeled by inclusion of spontaneous decay of double-vacancy configurations of the type $\mathrm{KM}\to M^2$. This multiplet model permitted extraction of partial cross sections for the production of ${\mathrm{KM}}_{\mathrm{I}}$ and ${\mathrm{KM}}_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ configurations. This report also contains new data on details of absorption fine structure in the region of the single-vacancy threshold and the principal double-vacancy thresholds.

In connection with a recent experiment of vacuum-ultraviolet generation in multiphoton resonant ionization of xenon at increasing pressure, a model is elaborated to account for the simultaneous effect of a laser excitation tuned near a three-photon resonance and a pressure-induced emission from the resonant state to the ground state. Under certain assumptions usual in various super-radiance treatments, a system of Bloch equations is derived and numerically solved. The dependence of the ionization probability and third-harmonic production versus the interaction time, gas pressure, dynamical detuning, and laser intensity is extensively studied. A transition between a high and low ionization rate is observed when the pressure increases simultaneously with the disappearance of Rabi oscillations and a saturation of third-harmonic generation. An order-of-magnitude calculation reveals that such phenomena are accessible to experiment and a qualitative comparison with the above-mentioned results in xenon is found to be satisfactory.

The newly observed $1s$ photoabsorption spectrum of sodium vapor is interpreted theoretically with the use of the conventional Racah-Slater model. The transitions $1s^{2}3s-1s3s3p$ are treated in detail. Only electrostatic interactions are significant. It is shown how the three Slater parameters $G_0\left(1s3s\right)$, $G_1\left(3s3p\right)$, and $G_1\left(1s3p\right)$ govern the line positions and their relative intensities to give good agreement with the observed spectrum.