The Sternheimer antishielding factor ${\gamma }_{\infty }$ has been calculated using nonrelativistic Hartree-Fock-Slater core-electron wave functions for several metallic elements in the third, fourth, and fifth rows of the Periodic Table assuming the ground-state electronic configuration for the transition-metal atoms to be $3d^{n}4s^1$, $4d^{n}5s^1$, and $5d^{n}6s^2$, respectively. These values have been compared with the available ${\gamma }_{\infty }$ values based on the free-ionic-core-electron wave functions. For the elements in the intermediate region of each row, the presently calculated ${\gamma }_{\infty }$ values are found to be significantly different from the frequently used free-ion values corresponding to the core-electron configuration.

In a measurement of emission of Balmer-$\alpha$ flux from atomic hydrogen or deuterium excited by electron impact in a crossed-beam experiment, a longitudinal electric field which enhances the Balmer-$\alpha$ flux by Stark-mixing components of like $M_J$ within the $n=3\mathrm{}$ shell, does so asymmetrically depending on whether the field is applied parallel or antiparallel to the electron beam. The effect is attributed to coherent excitation of states of opposite parity.

A modified Glauber amplitude proposed earlier by this author for electron-atom scatterings is applied to the analysis of elastic scattering of electrons by helium at various intermediate energies. The results are found to be in good agreement with experimental data acquired by various research groups with absolute measurements. Thus, the present work confirms reasonably clearly that the failure of the Glauber approximation for elastic scattering of electrons by helium stems mainly from the inadequacy of its second-order eikonal term. A comparison with results of other methods of approximation will also be made.

${\mathrm{H}}^{-}$ ions with energies of 0.5 and 1.0 MeV were passed through a crossed beam of Ar atoms. Secondary electron energy spectra in the energy region of $v_e\approx v_i$ were measured in the forward direction. These spectra seemed to manifest characteristics of two types of ionization processes. The results are discussed within the framework of theories of electron loss. A group of electrons was tentatively identified as being produced by the single-electron-loss process. Another group of electrons was interpreted as respresenting only a small portion of the electrons from double-electron-loss collisions.

We have measured the linear polarization of the 5016-Å, $2s{}_{}{}^1{}_{}{}^{}S-3p{}_{}{}^1{}_{}{}^{}P$ transition of Hei excited by a thin carbon foil perpendicular to the incident ${\mathrm{He}}^{+}$ beam at ion energies 50-500 keV. We find that the alignment of the $3p{}_{}{}^1{}_{}{}^{}P$ term depends upon the beam current density within the range (2-150 μA ${\mathrm{cm}}^{-2\mathrm{}}$) measured. Oscillations in the dependence of both $\frac{M}{I}$ (the linear polarization fraction) upon energy and the current density variation of $\frac{M}{I}$ with energy are observed. We discuss possible origins of these variations.

Total cross sections for charge transfer and impact ionization in ${\mathrm{C}}^{+6\mathrm{}}$-H collisions have been calculated for the range of relative velocities (0.1-10) × ${10}^8$ cm/sec. At the lower velocities [(0.1-2) × ${10}^8$ cm/sec] coupled-state calculations in an impact-parameter approximation were made of the charge-transfer cross sections using a basis set of exact one-electron two-center wave functions. An investigation of the origin dependence of these perturbed stationary-state calculations showed that differences of about 30% in the cross sections occur when the origin is shifted from the target to the ion center. At the higher velocities a classical-trajectory Monte Carlo approach was employed to determine both the charge-transfer and impact-ionization cross sections. The two sets of calculations are in reasonable agreement in the overlapping energy range, and give a comprehensive picture of the overall electron-removal cross section. They show that electron capture dominates in the region between 0.1 × ${10}^8$ and 3 × ${10}^8$ cm/sec with a peak cross section of ∼ 5 × ${10}^{15}$ ${\mathrm{cm}}^2$ at $v\approx 7\times {10}^7$ cm/sec. The capture is predominantly into the $n=4\mathrm{}$ levels of the product ${\mathrm{C}}^{+5\mathrm{}}$ ion. Impact ionization is found to be the most important electron removal process at velocities above 4 × ${10}^8$ cm/sec.

Microwave afterglow and grating spectrometric apparatus are used to study dissociative recombination in krypton. Over the electron temperature range $300\le T_e\le 8400$ K and with $T_{+}=T_{\mathrm{gas}}=300\mathrm{}$ K, the total rate coefficient may be represented by $\alpha \left[{{\mathrm{Kr}}_2}^{+}\right]=1.6\mathrm{}\times {10}^{-6\mathrm{}}{\left[\frac{300}{{\mathrm{T}}_e\left(\mathrm{K}\right)}\right]}^{0.55}$ ${\mathrm{cm}}^3$/sec, with an uncertainty of ± 10%. At thermal energy (300 K) excited states of Kr* having energies up to that of the ${\mathrm{Kr}}_2^{+}$ ion in its ground electronic and vibrational state are observed to result from the dissociative recombination. With microwave heating to $T_e\sim 7000$ K, additional, higher-lying Kr* states (up to ∼ 0.5 eV above the ${\mathrm{Kr}}_2^{+}$ ion ground state) are observed. In both cases the excited states most strongly populated by dissociative recombination appear to be the $5p$ states.

We present a vibrational-rotational close-coupling formulation of electron-diatomic-molecule scattering in a body-fixed frame, with the target molecular axis chosen to be the $z$ axis. The resulting coupled differential equation is solved in the moving body-fixed frame throughout the entire region of space. The coupled differential equation and asymptotic boundary conditions are given in terms of definite parity, which are necessary for reducing the number of coupled channels. Procedures for evaluating cross sections employing this body-fixed formulation are outlined, thus rendering the present formulation directly applicable to numerical calculations. We discuss the advantages of the body-fixed formulation over a space-fixed formulation for introducing approximation schemes, for studying resonance scattering of vibrational transition, and for electron-heavy-molecule collisions. Aside from the formal e$\stackrel{\mathrm{´}}{\mathrm{q}}$uivalence between the two formulations, conditions are also discussed for obtaining identical results from them when a (finite) truncated basic set is used.

The hybrid theory for low-energy electron-diatomic-molecule scattering, proposed by Chandra and Temkin, is systematically reformulated. It is shown that the hybrid theory can be equivalently derived from the vibrational-rotational (V-R) close-coupling theory when the dependences on the rotational quantum numbers are neglected in both the energy levels and the radial parts of V-R wave functions of target molecule. The expressions of scattering amplitude, differential, integral, and momentum-transfer cross sections of hybrid theory for the simultaneous V-R transition of target molecules obtained in our formulation are thus in the same form as those of V-R close-coupling theory. Distorted-wave Born approximation expressions for the cross sections of hybrid theory are also presented. It is pointed out that the neglect of rotational quantum number dependence in the radial part of wave functions is required to obtain fixed-nuclei approximation or hybrid theory, where the internuclear axis components of incident electron angular momentum $l_{z^{\prime }}$ are conserved. An $l_{z^{\prime }}$-conserving close-coupling approximation is proposed which is derived from the V-R close-coupling formulation in the moving body-fixed frame. This approach has a nature and simplicity similar to the original hybrid theory in that the $l_{z^{\prime }}$ conservation is satisfied, but the rotational motions of target molecule are partly taken into account.

Resonant angular distributions for low-energy electrons scattered by diatomic molecules are derived. For homonuclear molecules, our expression for vibrational excitation is equivalent to those of others. However, we are able to clarify the role of parity favoredness. For heteronuclear molecules, our expressions are new. In particular, they contain only one parameter and are necessarily symmetric about 90°. Furthermore, the individual rotational cross sections within the vibrational band can be determined in terms of the same parameter. Asymmetry about 90° is predicted for these. Finally, a theorem relating these integrated rotational cross sections is derived. Results for the angular distributions are given in tabular form for easy usage.

The experimental data for vibrational excitation of CO by electrons with incident energy of 1.8eV are analyzed using a recent theory. Though the theoretical expression for resonant angular distributions contains only one parameter, it fits the data very well allowing accurate determination of the parameter's value. Using this value, all rotational cross sections within the vibrational band are calculated.

Collisions of ground-state $\left(1\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ and metastable $\left(2\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ hydrogen atoms with rare gases and molecular hydrogen have been studied in the energy range 0.5-3.0 keV. For an acceptance angle of 55 mrad, the electron loss and the electron-capture cross sections of both $\mathrm{H}\left(1\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ and $\mathrm{H}\left(2\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ have been measured and compared with previous experimental values. The deexcitation cross section for $\mathrm{H}\left(2\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ has been deduced with the help of previously measured total-quenching cross sections for $\mathrm{H}\left(2\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$. The ratio of the electron-capture cross sections for $\mathrm{H}\left(2\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ relative to $\mathrm{H}\left(1\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ is found to be very large for argon at low energies. The effects of large-angle scattering and of highly excited states of H are discussed.

Total cross sections for single-electron capture by ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$ incident on atomic and molecular hydrogen have been measured in the velocity range (1-6)×${10}^8$ cm/sec. A classical-trajectory Monte Carlo method was also used to calculate the electron-capture and impact-ionization cross sections for ${\mathrm{He}}^{++}$ on H in this velocity range. The theoretical electron-capture cross sections are found to be in good agreement with the present experimental values at velocities above 2.5×${10}^8$ cm/sec, but tend to underestimate the experimental values by roughly 25% at the lowest velocities. The experimental ${\mathrm{He}}^{++}$ + H electron-capture cross sections are in excellent agreement with the measurements of Shah and Gilbody in the velocity region where the two experiments overlap. No significant isotope effect (${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$ versus ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$) could be discerned on the theoretical cross sections as a function of relative velocity.

Kinetic-energy spectra of the ${\mathrm{O}}^{+}$, ${\mathrm{O}}^{2+}$, and ${\mathrm{O}}^{3+}$ fragments produced by 1-MeV ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{+}$, and ${\mathrm{O}}^{+}$ projectiles have been obtained. The ${\mathrm{O}}^{+}$ spectrum resulting from ${\mathrm{H}}^{+}$ bombardment is similar to spectra obtained by electron bombardment and photoionization. In addition, an ${\mathrm{O}}^{2+}$ spectrum resulting from ${\mathrm{H}}^{+}$ bombardment has been obtained. The ${\mathrm{O}}^{+}$, ${\mathrm{O}}^{2+}$, and ${\mathrm{O}}^{3+}$ spectra obtained from ${\mathrm{He}}^{+}$ and ${\mathrm{O}}^{+}$ bombardment show energy groups for which approximate energy assignments have been made. The relative intensities of these energy groups are dependent on the projectile, with ${\mathrm{O}}^{+}$ projectile greatly enhancing the higher-energy groups relative to the ones of lower energy.

It was recently discovered that when there are sufficiently rapid spin-exchange collisions in an alkali-metal vapor, the rf magnetic-resonance frequency of the ground-state atoms becomes a constant fractional value (e.g., $\frac{4}{11}$ for Cs) of the Larmor frequency, and the linewidth becomes inversely proportional to the spin-exchange rate. These properties are in complete contrast to those in the slow spin-exchange limit. We present a theoretical analysis of these properties, and we predict some additional new effects for rapid spin exchange. Four theories are presented; an intuitive-vector model, a perturbation treatment, numerical solutions of complex non-Hermitian matrices, and a statistical analysis of the effect of rapid transfers between two Zeeman multiplets. These theories all provide, to varying degrees, consistent quantitative answers to the problem of how spin exchange affects magnetic resonance in an alkali vapor.

The deexcitation or quenching of the metastable $2S$ state of atomic hydrogen in collision with atoms and molecules has been studied using a beam-attenuation method in conjunction with a time-of-flight technique at velocities between 0.4 × ${10}^6$ and 4 × ${10}^6$ cm/sec (0.08 and 8 eV). In this regime, transfer of the metastable to the $2P$ state of hydrogen, followed by radiative decay to the ground state, is the dominant destruction mechanism. Absolute cross sections are reported for the quenching of $\mathrm{H}\mathrm{}\left(2S\right)\mathrm{}$ atoms in collision with the noble gases (helium-xenon), with molecules that have permanent electric-quadrupole moments (hydrogen and nitrogen), and with molecules that have permanent electric-dipole moments (ammonia, methanol, and acetone). For molecules with dipole moments, the cross sections are on the order of ${10}^{-13\mathrm{}}$ ${\mathrm{cm}}^2$ and vary approximately as $v^{-1\mathrm{}}$. For the noble gases and the quadrupole-moment molecules, the cross sections are on the order of ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ and vary approximately as $v^{-n}$ where $0.3<n<\mathrm{}0.7\mathrm{}$. Measurements of the relative cross section for the production of ultraviolet radiation in collision with nitrogen and argon are reported, and the cross sections for the quenching of $\mathrm{H}\mathrm{}\left(2S\right)\mathrm{}$ and $\mathrm{D}\mathrm{}\left(2S\right)\mathrm{}$ in argon are compared. Data for the noble gases indicate that large-angle elastic scattering is probably not responsible for the discrepancy between theory and experiment. The data for molecular hydrogen suggest that short-range forces are important in collisions with molecules possessing a quadrupole moment.

The development of projectile $K$ vacancies in heavy ions passing through solids has recently been studied using both target and projectile x-ray yields. The analysis of these results implies that the post-foil charge-state fractions will exhibit a target thickness dependence which is related to the vacancy production and quenching processes for the $K$ shell of the projectile as it moves in the solid. We report experimental results for the charge-state fractions of 54-MeV S ions on thin foils of C, Al, Ti, and Ni. We propose a model which accounts for both the target thickness and the target-atomic-number dependences of the individual charge-state fractions.

We have measured the alignment and orientation parameters of forward-scattered argon ions excited in grazing-incidence collisions with a Cu surface. The polarization of the light emitted from excited scattered ions has been measured simultaneously with a measurement of their spatial position relative to the interaction region. We have measured the dependence of the orientation with ion energy, incidence angle, scattering angle, and surface material. Total ion angular distributions are found to be independent of incident energies between 0.50 and 3.0 MeV. Possible excitation mechanisms for producing the observed charge states, excited states, alignment, and orientation are discussed. We compare this surface excitation with the excitation of ions passing through thin foils.

Stopping power of Al, Cu, Ag, and Au for 0.8-7.2-MeV/amu hydrogen, helium, and lithium ions has been measured by the calorimetric-compensation method to an accuracy of 0.5%. The data agree with most other published results and confirm the validity of earlier measurements by Andersen and co-workers. Higher-order $Z_1$ deviations from the Bethe formula have been examined. The experimental results agree with Lindhard's calculation of the $Z_1^3$ correction combined with a $Z_1^4$ term, which is slightly larger than Bloch's value. The experimental higher-order $Z_1$ contributions have a significant influence on the evaluation of empirical shell corrections, and the data are used to extract more realistic values. The deduced shell corrections show good agreement with Bonderup's calculations.

The standard time-independent formulation of nonrelativistic scattering theory is here extended to take into account the presence of an intense external radiation field. In the case of scattering by a static potential the extension is accomplished by the introduction of asymptotic states and intermediate-state propagators which account for the absorption and induced emission of photons by the projectile as it propagates through the field. Self-energy contributions to the propagator are included by a systematic summation of forward-scattering terms. The self-energy analysis is summarized in the form of a modified perturbation expansion of the type introduced by Watson some time ago in the context of nuclear-scattering theory. This expansion, which has a simple continued-fraction structure in the case of a single-mode field, provides a generally applicable successive approximation procedure for the propagator and the asymptotic states. The problem of scattering by a composite target is formulated using the effective-potential method. The modified perturbation expansion which accounts for self-energy effects is applicable here as well. A discussion of a coupled two-state model is included to summarize and clarify the calculational procedures.