A list is assembled of the emission lines produced by the charge transfer of doubly and trebly charged ions of carbon, nitrogen, oxygen, and neon in collision at low energies with atomic hydrogen. Rate coefficients of 2.0×${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$${\mathrm{s}}^{-1\mathrm{}}$ for the process ${\mathrm{O}}^{3+}$+H→${\mathrm{O}}^{2+}$ ($2p3p$, ${}_{}{}^1{}_{}{}^{}P$) +${\mathrm{H}}^{+}$ and of 2.1×${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$${\mathrm{s}}^{-1\mathrm{}}$ for the process ${\mathrm{O}}^{3+}$+H→${\mathrm{O}}^{2+}$ ($2p3p$, ${}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{}$) at 1 eV are obtained by comparing observations of planetary nebulae with detailed models.

Absolute emission cross sections for the (0,1), (1,2), and (2,3) band emission sequence of the ${\mathrm{N}}_2^{+}$ first-negative system have been measured for low-energy ${\mathrm{H}}^{+}$ and H collisions with room-temperature ${\mathrm{N}}_2$ molecules. The energy range covered for ${\mathrm{H}}^{+}$ impact was from 63 eV to 2.0 keV, and that for H impact was from 160 eV to 2.5 keV. For H+${\mathrm{N}}_2$ collisions, cross sections for ${\mathrm{N}}_2$ second-positive emissions for the (1,5) and (2,6) emission bands were also determined. The total cross sections for production of ${\mathrm{N}}_2^{+}$($B$) and ${\mathrm{N}}_2$($C$) were determined from these measured results. The techniques used to accomplish the measurements are described, and the cross sections obtained are compared with the results of other investigations.

A new iterative method for solving scattering integral equations for local as well as nonlocal potentials is proposed. The scattering matrix is expressed in the form of a continued fraction. This method converges extremely fast for compact potentials with arbitrary strength. A high precision of the result is expected with a relatively small amount of numerical work. Starting from the second iteration, all functions which are to be computed in the course of iterations are regular at the origin and are of finite range in configuration space. The method is applied to the elastic scattering of electrons from hydrogen atoms in the static, exchange approximation. Its efficiency is compared with some recently proposed methods.

The intensity of the pure rotational absorption spectrum of gaseous HD is measured as a function of density for pure HD and HD-He and HD-Ar mixtures. The decrease in the absorption coefficient with increasing density is consistent with a destructive intracollisional interference between the transitions involving the permanent and collision-induced dipole moments. The permanent dipole moment of the molecule in its ground vibrational state is found to be $J$ dependent and in the range (8-10)×${10}^{-4\mathrm{}}$ D.

Equilibrium charge-state distributions of Cu ions behind carbon foils have been measured in the energy region 35—146 MeV. The equilibration is obtained with about 30- and 50-μg/${\mathrm{cm}}^2$-thick carbon at energies of 65 and 120 MeV, respectively. Almost-constant values of distribution width have been observed in the 35—47-MeV and 96—146-MeV energy regions. The former corresponds to the Cu ions whose outermost electrons are mainly distributed in the $M$ shell, while the latter in the $L$ shell. The asymmetry of the charge distribution has been observed in the boundary charge state between the Cu $L$ and $M$ shells. Such an asymmetric distribution function has been well approximated with the connection of two Gaussian distributions with an equal centroid but with different standard deviations.

Relative populations of terms in Cii, Ciii, and Civ, excited after the passage of ${\mathrm{C}}^{+}$ ions through a carbon foil, have been measured as a function of the projectile energy ($0.3<E<\mathrm{}2.3\mathrm{}$ MeV). These excitation functions are shown to depend on the energy of the term and, in Cii, a dependence on the core configuration of the term is observed at low projectile energies ($E<\mathrm{}0.6\mathrm{}$ MeV). The excitation functions are also compared to the charge-state-fraction curves as a function of the ion energy and this comparison generally allows an unambiguous identification of the charge of the ion emitting an unclassified transition in Cii, Ciii, and Civ.

Energy dependence of the ${\mathrm{H}}^{+}$-He differential cross section is analyzed for a fixed scattering angle. The energy range is between 0.1 and 0.7 eV. Rather complex resonance structure is found in which it is difficult to isolate the contribution of a single resonance.

The positronium-formation cross sections in positron-helium scattering have been calculated with the use of a distorted-wave polarized-orbital method from the threshold to 100 eV. The results with and without the matrix elements involving the distorted target wave functions are found to differ appreciably. The results of the first Born approximation are not expected to be correct even at the incident-positron energy 100 eV. The measured values at 20 eV are found to be less than ½ of the present predicted values. The sharp rise of the formation cross section within the ore-gap region as observed by Charlton et al. has also been noticed by us. The minimum in the differential cross section has been found at all energies as in the case of hydrogen atom.

The atom-atom momentum-transfer cross section is analyzed for low-energy collisions in which resonances may be present. It is shown that their contribution to this cross section can be substantial, and this is confirmed in the calculation on ${\mathrm{H}}^{+}$-He system.

The differential cross section for photon scattering from relativistic polarized free electrons in motion is derived. The calculation extends early results from electrons at rest. It is argued that the present derivation is required for use in bound-state spin-dependent Compton scattering from polarized electrons. The results provide an alternative check on recent work carried out using a quasi-relativistic Hamiltonian.

The effective ionization rates of Ti ix, Ne vi, Ne vii, and O vi have been measured with the use of the plasma spectroscopy method in a $\theta$ pinch discharge at an electron temperature (50-60 eV) much below their ionization threshold and at an electron density of (≃ 2-3)×${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$. A theoretical analysis of the effective ionization rates showed that excitation ionization is a major contributing process. Theoretical values are in reasonable agreement with experiment.

The photoionization of hydrogen atoms in a strong magnetic field is formulated as a multichannel problem by representing the asymptotic electron wave function in cylindrical coordinates. Departures from cylindrical symmetry close to the nucleus are incorporated by an $R$-matrix treatment at short range, which then merges with standard quantum-defect procedures. The $R$-matrix calculation utilizes the eigenchannel approach, recast in noniterative form. At the field strength treated here, $B=4.7\mathrm{}\times {10}^9$ G, the photoionization cross section displays narrow "autoionizing" resonances near the excited Landau thresholds.

When a low-pressure (${10}^{-2\mathrm{}}$-Torr) sample of ${\mathrm{N}}_2$ or CO is exposed to a beam of linearly polarized synchrotron radiation (18-34 eV), electronically excited molecular ions are formed whose subsequent unresolved emission is found to be partially polarized. The degree of polarization of the ${\mathrm{N}}_2^{+}$ $B{}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}-X{}_{}{}^2{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ fluorescence (∼391 nm) and the C${\mathrm{O}}^{+}$ $B{}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}-X{}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ fluorescence (∼220 nm) is studied as a function of the energy of the ionizing radiation from threshold to higher energies. This information determines the alignment of the photoion, which in the case of ${\mathrm{N}}_2$ must be corrected for depolarization caused by spin-rotation and hyperfine interaction. From the polarization of the fluorescence we deduce $\gamma$, the ratio of parity-unfavored to the sum of parity-favored contributions for photoelectron ejection. Comparison of the dynamical channel ratio $\gamma$ with theoretical calculations for $\sigma$- and $\pi$-photoelectron ejection shows poor agreement for ${\mathrm{N}}_2$ and fair agreement for CO.

A recently proposed method of optogalvanic double-resonance (OGDR) spectroscopy, which employs two cw lasers modulated at different frequencies and a dc discharge, has been investigated theoretically as well as experimentally. The technique is demonstrated to provide a versatile, state-selective spectroscopic method. A detailed analysis has been carried out for different situations where two lasers pump transitions which have the lower and/or upper state, or no state, in common. It also shows that the OGDR signal detected at the sum or difference modulation frequency can be given as a linear combination of the perturbed population densities in a plasma which give rise to the single-resonance signal. In addition, the results show that the OGDR signal polarity is characteristic for each type of double resonance. This has been verified in an OGDR experiment using a hollow-cathode discharge in neon and two cw dye lasers. State-selective OGDR spectra have been compared with optical-optical double-resonance spectra. Useful applications and advantages of the OGDR spectroscopy are discussed.

The $K\alpha$ hypersatellites $K{\alpha }_1^h$ and $K{\alpha }_2^h$ of zirconium were observed in a conventional x-ray spectrum analysis. The energy separation between the hypersatellites and their corresponding diagram lines were measured, and the intensity ratio $\frac{I\left(K{\alpha }_1^h\right)}{I\left(K{\alpha }_2^h\right)}$ was computed. The experimental values are in good agreement with the results of the most advanced calculations, except for the energy of the $K{\alpha }_2^h$ where the measured value is some 15 eV higher than the theoretical prediction.

A method to obtain subnatural resolution in laser-induced fluorescence spectroscopy by phase switching is described. The subnatural linewidth is obtained by extracting a coherent transient response induced by the switching of the laser. The linewidth in this type of spectroscopy is determined by the time interval between the switching and observation, instead of the spontaneous lifetime. The result is compared with the experiment on the Na $D_1$ line.

The broadening of the Na resonance lines, due to collisions with Rb and with Cs, has been measured with the use of the normalized fluorescence-intensity method of Chatham, Lewis, and Gallagher. Several Na resonance-radiation diffusion and absorption corrections were necessary in the Rb case, due to an unavoidable excess of Na density in the Rb vapor. The line-broadening rate coefficients $k_1$ and $k_2$ for the $D_1$ and $D_2$ resonance lines are $k_1\left(\mathrm{Rb}\right)=(6.2\mathrm{}\pm 0.4)\times {10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{-1\mathrm{}}$, $k_2\left(\mathrm{Rb}\right)=(5.5\mathrm{}\pm 0.6)\times {10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{-1\mathrm{}}$, $k_1\left(\mathrm{Cs}\right)=(6.9\mathrm{}\pm 1.0)\times {10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{-1\mathrm{}}$, and $k_2\left(\mathrm{Cs}\right)=(5.5\mathrm{}\pm 0.9)\times {10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{-1\mathrm{}}$ at $T\simeq 300$° C. The leading ($C_6{R}^{-6\mathrm{}}$) dipole-dipole long-range dispersion forces for the Na-Rb and Na-Cs interactions are calculated, and are used in the impact-theory formula to obtain theoretical line-broadening rate coefficients. These are in poor agreement with the measurements, indicating that as suggested by Vadla, the higher-order ($C_8{R}^{-8\mathrm{}}$) dispersion terms are also important at the very long range responsible for this line broadening.

Stark widths and shifts of Si ii lines from five visible multiplets: (1) $3p^2{}_{}{}^2{}_{}{}^{}D-4p{}_{}{}^2{}_{}{}^{}P_{}^o{}_{}{}^{}$, (2) $4s{}_{}{}^2{}_{}{}^{}S-4p{}_{}{}^2{}_{}{}^{}P_{}^o{}_{}{}^{}$, (3) $3d{}_{}{}^2{}_{}{}^{}D-4f{}_{}{}^2{}_{}{}^{}F_{}^o{}_{}{}^{}$, (4) $4p{}_{}{}^2{}_{}{}^{}P_{}^o{}_{}{}^{}-5s{}_{}{}^2{}_{}{}^{}S$, and (5) $4p{}_{}{}^2{}_{}{}^{}P_{}^o{}_{}{}^{}-4d{}_{}{}^2{}_{}{}^{}D$, are measured in an electromagnetically driven $T$ tube. Electron density [(0.3-1.4)×${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$] is determined by laser interferometry, and from $\mathrm{H}\beta$ profiles. Temperature (16000-22000 K) is obtained from the intensity ratios of Si iii and Si ii lines, and from Boltzmann slopes of Ne i lines. Results are compared with other experimental and theoretical data.

A model for laser-induced autoionization is considered which includes two qualitatively different relaxation mechanisms: radiation damping to the ground state and phase fluctuations. Analytic solutions are presented for the first- and second-moment correlation functions of the atomic and photon operators in the Heisenberg picture. We present an explicit analysis of the spectrum of emitted photons at long times and investigate the effect of both relaxation mechanisms, as well as the influence of detuning and laser intensity, on this photoemission spectrum.

$N$ two-level "atoms" are considered in interaction with a single-mode resonant electromagnetic field. The exact solution is given nonrelativistically for all times for the case of spontaneous emission, when only one atom is initially excited. The solution is given for the general case of the $N$ atoms in inequivalent mode positions.