The generalized oscillator strengths for the 3s-3p and 2p-3s excitation processes have been obtained from the related differential cross sections, measured at 1-keV impact energy and normalized to the first-Born-approximation (FBA) result for the 3s-3p process at the scattering angle of 2°. Theoretical values for the 3s-3p excitation process were also determined using the Glauber approximation, both considering the interaction of the incident electron with the atomic electrons not directly involved in the excitation process and (N-1) nuclear charges and by neglecting this interaction. FBA results were determined for both the 3s-3p and 2p-3s processes. Theoretical values for the elastic differential cross section were also determined.

The complex-coordinates approach in scattering theory is extended to the time-dependent Schrödinger equation by using Simon’s exterior scaling contour, and it is shown to cause outgoing wave packets to vanish for large distances in collision problems. Numerical applications are given for one- and two-dimensional problems where the complex-coordinates method is shown to eliminate reflections of outgoing wave packets from the boundaries of the coordinate space grid used in the calculations. The extension of the exterior scaling approach to the time-dependent description of a charged particle in dc and ac electromagnetic fields is given, and numerical results on these problems are also presented.

Analytic expressions for 1s-nlm differential-capture cross sections in proton-hydrogen collisions are derived. We employ the partially peaked impulse approximation and retain terms up to first order in an expansion of the Fourier transform of the potential. The exact impulse approximation is also computed using numerical integration of a three-dimensional integral. The exact and analytic calculations are compared with each other and with experiment.

Using synchrotron-radiation-based angle-resolved photoelectron spectroscopy, the relative partial photoionization cross sections for the production of the ${}_{}{}^4{}_{}{}^{}$${\mathit{S}}^{\mathit{o}}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{o}}$ ionic states in atomic oxygen, as well as the corresponding asymmetry parameters, are measured from threshold at 13.62 to about 30 eV. The cross sections are placed on an absolute scale using previous data obtained with an electron spectroscopy modulation method. Attention is focused on the numerous autoionization resonances below the 2${\mathit{p}}^{\mathrm{-}1}$ ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{o}}$, 2${\mathit{p}}^{\mathrm{-}1}$ ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$, and 2${\mathit{s}}^{\mathrm{-}1}$ ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}^{\mathit{e}}$ limits. The behavior of the asymmetry parameters across these resonances is observed for the first time. The 2s2${\mathit{p}}^4$${(}^4$${\mathit{P}}^{\mathit{e}}$)3p${(}^3$${\mathit{S}}^{\mathit{o}}$${,}^3$${\mathit{P}}^{\mathit{o}}$${,}^3$${\mathit{D}}^{\mathit{o}}$) resonances are fitted by a Fano-type profile to obtain accurate values for the position, width, and q parameter.

Measurements of collision-induced emission in the fundamental vibration-rotation band of hydrogen are presented for argon, xenon, and neon collision partners. These absolute, spectrally resolved infrared measurements were performed at high densities behind reflected shock waves over the temperature range of 900–3400 K. The emission was found to be dominated by Q-branch transitions at high temperature due primarily to the dipole moment induced by the overlap between the electron clouds of the collision pair. The strength of this interaction was evaluated from the data and compared with similar evaluations determined from low-temperature absorption studies.

The Fock-Tani Hamiltonian is found for scattering processes involving up to two ions and two electrons. Possible bound-state species include one or two electrons bound on an ion fixed at the origin, and a one-electron projectile atom. A diagrammatic technique is illustrated that simplifies the algebra of the transformation. Coulomb- or plane-wave states are automatically generated by the same asymptotic Hamiltonian for all arrangement channels.

We calculate eigenenergies for bound states of electrons in the dynamical screening potential of a fast charged particle traversing a solid by diagonalization of Hamiltonian matrices in a truncated Hilbert space of 600 hydrogenic basis states. Application of classical scaling invariances yields a universal energy-level diagram. A simple approximate formula for projectile-centered one-electron bound states is obtained. We find velocity thresholds for the existence of excited states which are in surprisingly good agreement with recent data by Chevallier et al. [Phys. Rev. A 41, 1738 (1990)].

It is known that ultrarelativistic electrons, when moving nearly parallel to an axis in a single crystal, will emit very intense radiation containing high-energy quanta. The radiation spectra are connected to synchrotron spectra in excessively strong magnetic fields. The latter spectra have previously been calculated by quantum perturbation theory, and are much reduced compared to the corresponding classical spectra. By application of the correspondence principle, it is shown that, for spin-zero particles, the complete quantum spectrum is obtained exactly from the classical spectrum by a simple modification of the frequency variable. The result holds for arbitrary external fields and with respect to angular distribution, polarization, and frequency distribution. Agreement with previous calculations of the synchrotron case is verified. For spin-1/2 particles the quantum frequency spectrum can be expressed with satisfactory accuracy by the classical radiation of spin-zero particles. These results may be of assistance in our understanding of radiation by ultrarelativistic particles.

The stopping power of protons and antiprotons moving at low velocities through a uniform temperature-dependent electron gas is calculated by making use of the momentum-transfer cross section. The screened scattering potential required is determined with the aid of a parametric dielectric function obtained from the linearized Thomas–Fermi–von Weizsäcker treatment for screening in extended systems. A nonperturbative constraint, provided by the nuclear-cusp condition for the total electron density at the position of the probe charge, is used to fix the parameter value. The temperature-dependent higher-order effect on the stopping power is discussed for metallic densities of the system, showing that first-order approximations are valid only asymptotically.

We develop a model with ${\mathit{H}}_{\mathit{q}}$(4) and ${\mathrm{SU}}_{\mathit{q}}$(2) quantum group symmetries to describe the vibrational and rotational spectra of diatomic molecules. The representations of ${\mathit{H}}_{\mathit{q}}$(4) and ${\mathrm{SU}}_{\mathit{q}}$(2) and solutions to the quantum systems of q oscillators and q rotators are provided. We emphasize that the energy spectra of the q oscillator and q rotator exhibit remarkably the properties of the infrared, vibrational, and rotational Raman spectra as well as vibrational and rotational structures of electronic transitions of the diatomic molecule. When the parameters are properly selected, the spectra of this model coincide with the observed spectra of diatomic molecules. It is suggested that ${\mathit{H}}_{\mathit{q}}$(4) ⊗${\mathrm{SU}}_{\mathit{q}}$(2) is an essential symmetry of vibrations and rotations in diatomic molecules.

Experimental 1s linewidths for compounds containing carbon, nitrogen, and oxygen are much greater than those predicted for the free atoms. Using a one-center model, we have determined the effect of molecular composition on the linewidth. The predicted linewidth in methane is 1.7 times that for a carbon atom. Increasing the electronegativity of ligands decreases the predicted linewidth; this result is in contrast to the predictions of the multicenter model [E. Hartmann, J. Phys. B 21, 1173 (1988)]. Except for ${\mathrm{CO}}_2$, the theoretical linewidths are in good agreement with experiment.

Highly excited states of neutral CO lying in the 20–40-eV excitation energy range, i.e., up to the double-ionization threshold energy, are studied by means of synchrotron radiation. They are observed as resonances in the ion-yield curves, which measure the ${\mathrm{O}}^{\mathrm{-}}$ and ${\mathrm{C}}^{\mathrm{-}}$ negative-fragment-ion intensity as a function of the photon excitation energy. Narrow resonances are assigned to doubly excited Rydberg-state series converging to ${\mathrm{CO}}^{+}$ satellite states.

Measurements of the rotationally resolved absorption spectrum of the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}_{}^{20}{}_{}{}^{}$Ne and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}_{}^{20}{}_{}{}^{}$Ne 3${\mathit{s}}^2$${\mathrm{\Sigma }}^{+}$←2p ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }$ transition have been made. For each isotope, 13 vibrational transitions from the lower 2 ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }$ (v’’=0,1,2,3) to the upper 3${\mathit{s}}^2$${\mathrm{\Sigma }}^{+}$ (v’=0,1,2,3,4,5) electronic state have been observed and rotationally analyzed. For the 2 ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }$ state a well depth of 212(5) ${\mathrm{cm}}^{\mathrm{-}1}$ and an equilibrium separation of 4.36(2)${\mathit{a}}_0$ have been obtained. Analysis of the 3${\mathit{s}}^2$${\mathrm{\Sigma }}^{+}$ electronic state using an inverted perturbation analysis has revealed that the potential for this state displays, at large internuclear separations, a barrier greater than 60.6 ${\mathrm{cm}}^{\mathrm{-}1}$ above the atomic Li 3s asymptote. The well region has a minimum of 570(7) ${\mathrm{cm}}^{\mathrm{-}1}$ located at 4.11(1)${\mathit{a}}_0$. An anomalously large fine-structure constant of A=2.77(3) ${\mathrm{cm}}^{\mathrm{-}1}$ was determined for the 2${\mathit{p}}^2$Π (v’’=0) level.

High-resolution inverse Raman spectroscopy has been used to measure the self-broadening coefficients of the Raman Q-branch transitions in pure (natural) hydrogen. Measurements of six lines [Q(0)–Q(5)] were made at pressures from 2 to 50 atm and from 295 to 1000 K. The dependence of the derived broadening coefficients on temperature and rotational quantum number is analyzed using the energy-corrected sudden scaling law [A. E. DePristo, J. Chem. Phys. 73, 2145 (1980)]. We discuss three models for the J dependence of the pure-vibrational dephasing and find that models with little or no J dependence in the pure-vibrational dephasing are preferred.

The emission of the third excimer continuum of argon in the wavelength range between 175 and 250 nm has been studied by time-resolved optical spectroscopy. Argon gas at pressures between 5 and 100 kPa was excited with a pulsed beam of 100-MeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}_{}^{9+}{}_{}{}^{}$ ions from the Munich tandem van de Graaff accelerator. Wavelength spectra recorded in different time windows after the 2-ns beam pulses show that two different components contribute to the third continuum of argon. A radiative lifetime of 5.71±0.08 ns for the ${\mathrm{Ar}}_2^{2+}$ molecule and a rate coefficient ${\mathit{k}}_3$=(1.46±0.12)×${10}^{\mathrm{-}30}$ ${\mathrm{cm}}^{\mathrm{-}6}$/s for the reaction ${\mathrm{Ar}}^{2+}$+2Ar→${\mathrm{Ar}}_2^{2+}$+Ar were determined from the pressure dependence of time spectra at a wavelength of 190 nm. Additional time spectra were measured at 210 and 230 nm.

The ${\mathrm{H}}_{\mathrm{\beta }}$ line shifts were measured in dense ssT-shaped-tube plasmas for electron densities from 2.1×${10}^{17}$ to 7.8×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and temperatures between 19 000 and 35 000 K. Comparisons of these shifts with recent theories [H. R. Griem, Phys. Rev. A 28, 1596 (1983); 38, 2943 (1988)] that take the dynamical quadratic Stark effect for Δn=0 and n’=n+1 interactions and ion quadrupole effects into account are presented. Also, comparisons with some experimental results [H. L. Wiese, D. E. Kelleher, and D. R. Paquette, Phys. Rev. A 6, 1132 (1972)] were made. Our results are in agreement with an extrapolated experimental best fit to the experimental results of Wiese et al., but the measured shifts are larger than the theories predict.

The spectrum of triply ionized xenon (Xe iv) has been observed in the region 570–6900 Å. The configurations 5${\mathit{s}}^2$5${\mathit{p}}^2$5d and 5${\mathit{s}}^2$5${\mathit{p}}^2$6s have been studied and the energy levels reported for these configurations by Moore [Atomic Energy Levels, Natl. Bur. Stand. Ref. Data Ser., Natl. Bur. Stand. (U.S.) Circ. No. 467 (U.S. GPO, Washington, D.C., 1971)] were revised and extended to include seven new levels. The configuration 5s5${\mathit{p}}^4$ was included in the analysis to take into account the strong interaction between this configuration and 5${\mathit{s}}^2$5${\mathit{p}}^2$5d. Configuration-interaction Rydberg series have been also included in the calculations. This investigation was supported by Hartree-Fock calculations.

The electron affinities of atomic hydrogen and deuterium have been determined by tunable-laser threshold-photodetachment spectroscopy: the electron affinities of H (F=0) and D (F=1/2) are 6082.99±0.15 and 6086.2±0.6 ${\mathrm{cm}}^{\mathrm{-}1}$, respectively. The value for H is a 20-fold improvement over previous experimental determinations.

We give a simple semiclassical derivation of the radiative mean lifetime τ(${\mathit{n}}_{\mathit{r}}$) of an electron in a bound state in a uniform magnetic field B, that is, in a Landau state. The state is characterized by two quantum numbers ${\mathit{n}}_{\mathit{r}}$ and ${\mathit{n}}_{\mathit{l}}$ and by the velocity component ${\mathit{v}}_{\mathit{z}}$ of the electron parallel to B, but τ is independent of ${\mathit{n}}_{\mathit{l}}$ and ${\mathit{v}}_{\mathit{z}}$; ${\mathit{n}}_{\mathit{r}}$ and ${\mathit{n}}_{\mathit{l}}$ are the right and left circular Landau quantum numbers. The approach used is similar to that which has been applied in the semiclassical estimation of the radiative mean lifetime τ(n,l) of an electron in a hydrogenlike state with quantum numbers n and l. As in that case, the results become exact only in the limit in which the relevant quantum number(s)—in the present case ${\mathit{n}}_{\mathit{r}}$—approach infinity, but τ(${\mathit{n}}_{\mathit{r}}$) is reasonably accurate even for ${\mathit{n}}_{\mathit{r}}$ rather small. ${\mathit{L}}_{\mathit{z}}$, the z component of the orbital angular momentum of an electron in the field B=Be${\mathrm{^}}_{\mathit{z}}$, need not normally be considered, since the equation of motion is known. (The equation is gauge independent and only the rate of change of ${\mathit{L}}_{\mathit{z}}$ is necessary to estimate the mean lifetime.) However, since the change in ${\mathit{L}}_{\mathit{z}}$ accounts for the angular momentum given up to the photon which is radiated and since ${\mathit{L}}_{\mathit{z}}$ is formally gauge dependent, it is worth studying by itself. We evaluate ${\mathit{L}}_{\mathit{z}}$ in several ways; in one evaluation, the field B=Be${\mathrm{^}}_{\mathit{z}}$ is simulated by a magnetic monopole placed at a great distance from the circulating electron. We find that ${\mathit{L}}_{\mathit{z}}$ is half the mechanical orbital angular momentum and therefore that the field contribution to the total angular momentum cannot be omitted when applying angular momentum conservation.

Measurements of polarization of the Na 3${\mathit{p}}^2$${\mathit{P}}_{3/2}$ level produced in Na-Ar, Na-Kr, and Na-Xe optical collisions are reported. The measurements extend over a range of detunings from 150 ${\mathrm{cm}}^{\mathrm{-}1}$ red to 350 ${\mathrm{cm}}^{\mathrm{-}1}$ blue of resonant excitation of the Na 3p levels. The short-pulse, pump-probe technique employed in the experiments eliminates large systematic effects due to the hyperfine interaction, collisions, and radiative trapping. For far-blue-wing excitation, nearly constant polarizations of 21(2)%, 13(2)%, and 8(2)% are obtained for Na-Ar, Na-Kr, and Na-Xe, respectively.