The coupled-channel optical method solves a set of coupled momentum-space integral equations for a finite set of reaction channels. The remaining channels, including the target continuum, are described by the polarization potential operator, which formally depends on the full three-body state vectors for these channels. The distorted-wave optical potential makes the distorted-wave Born approximation for these state vectors, using exact target states. No other approximation is made. Calculations and comparison with experiment are reported for total ionization cross sections and asymmetries, total excitation cross sections, entrance-channel phenomena, and the coupled 1s,2s,2p channels, at a range of energies.

Absolute differential cross sections for charge-transfer scattering of ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ from molecules are reported over the laboratory angular range 0.02°–1.0°. Cross sections have been determined at 0.5, 1.5, and 5.0 keV for collisions of ${\mathrm{H}}^{+}$ with ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$, and at 1.5 keV for collisions of ${\mathrm{H}}^{+}$ with CO, ${\mathrm{CO}}_2$, NO, and ${\mathrm{CH}}_4$, and of ${\mathrm{He}}^{+}$ with ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, CO, and NO. The data exhibit considerable structure over the experimental angular range. Absolute integral cross sections from 0° to 1.0° have been obtained and are compared with the published total cross sections.

The dominant processes for producing near-zero-energy projectile-frame protons in ${\mathrm{H}}_2^{+}$-He collisions at 4-keV ion energy have been experimentally identified. The 1s${\mathrm{\sigma }}_{\mathit{u}}$ to 2p${\mathrm{\pi }}_{\mathit{u}}$ and 3d${\mathrm{\sigma }}_{\mathit{g}}$ transitions that produce these protons occur at internuclear separations of the ${\mathrm{H}}_2^{+}$ ion that are 2.5–3 times the equilibrium separation.

A semiclassical treatment based on a molecular orbital expansion is used to study ion-pair formation and Penning- and associative-ionization processes in ${\mathrm{He}}^{\mathrm{*}}$(2 ${}_{}{}^{1,3}{}_{}{}^{}$S)+Li collisions in the energy regime from 100 to 1000 eV. Although these processes are usually important in different energy ranges, here they are found to compete with each other to an appreciable degree and hence to provide a rare opportunity for investigating collision dynamics that require an equal-footing treatment between autoionization to the continuum and a discrete transition. The present cross sections for these processes compare favorably with the measurement of Wang, Tang, and Neynaber [J. Phys. B 20, 1527 (1987)].

Rate constants for the reaction ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}_{}^{+}{}_{}{}^{}$${+}^{20}$Ne${\to }^{20}$${\mathrm{Ne}}^{+}$${+}^{22}$Ne have been measured as a function of average center-of-mass kinetic energy (〈${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$〉) at each of three temperatures: 193, 296, and 464 K. The measurements were made in the range of 〈${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$〉 from 0.02 to 1 eV. The temperature dependence of the rate constant was determined for the first time and is of the form ${\mathit{T}}^{0.29}$. The rate constants measured as a function of 〈${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$〉 at the different temperatures depend only on 〈${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$〉 and not on experimental temperature for a given 〈${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$〉, as expected. Measured reduced mobilities are also reported for ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}_{}^{+}{}_{}{}^{}$ drifting in He. Classical trajectory calculations of the rate constants have been performed using the probability function of Rapp and Francis [J. Chem. Phys. 37, 2631 (1962)], and Dewangen [J. Phys. B 6, L20 (1973)] [as corrected by Gerlich (private communication)] as a function of internuclear separation. The theoretical rate constants are 10–30 % higher than the measured values.

Differential excitation cross sections have been measured for Kr 4${\mathit{p}}^6$${(}^1$${\mathit{S}}_0$)→4${\mathit{p}}^5$${(}^2$${\mathit{P}}_{1/2,3/2}$)5s transitions at 300- and 500-eV impact energies and for 1.5°–10° scattering angles by electron-energy-loss spectroscopy. The integrated cross sections for these impact energies are reported here. The generalized oscillator strengths have also been obtained to determine the optical oscillator strengths. The errors are estimated to be less than 15%.

Collision data in forms currently available from experimental sources are reduced by quadratures and algebraic transformations to dynamical parameters. The reduction hinges on suitable normalizations and utilization of sum rules and removes the influence of experimental geometries. The dynamical parameters, labeled by angular momenta restricted to a modest range, appear more suited to comparison with theory than the original experimental data. Our analytical developments are simplified by certain restrictions, whose removal is discussed in a final section.

The procedure of the preceding paper [Bohn and Fano, Phys. Rev. A 41, 5953 (1990)] has been applied to extract dynamical parameters of the collision process e(80 eV)+He(1 ${}_{}{}^1{}_{}{}^{}$S)→e+He(2 ${}_{}{}^1{}_{}{}^{}$P). These parameters, free of the experimental geometry, have been unraveled from the experimental polarization data available and their roles in the excitation and the alignment of the target have been analyzed.

The results are presented of further studies of the effects of electric fields on the photodetachment cross section of ${\mathrm{H}}^{\mathrm{-}}$, for both π and σ polarization. Data are fitted to the theory of Rau and Wong [Phys. Rev. A 37, 632 (1988)], which predicts a modulation about the zero-field cross section. Agreement is good for π polarization, but the predicted profile for σ polarization does not appear to match the data quite as well.

An annular-ring scattering geometry has been adopted to allow for scattering in the angular range 5°–15°. Measurements are made of differential coherent scattering cross sections of 279- and 662-keV γ-ray photons for Cu, Sn, and Pb. A critical dependence of photon attenuation upon transverse target thickness, demanding target thicknesses considerably less than one mean free path, is confirmed. Comparison of the results of experiment, with state-of-the-art theoretical predictions based upon a second-order perturbative approach, show comprehensive agreement to within the stated experimental-error limits.

Superelastic electron scattering from laser-excited ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$(. . .6s6p ${}_{}{}^1{}_{}{}^{}$P) is investigated both theoretically and experimentally. The theoretical framework is developed and incorporated into a model of a realistic scattering geometry of finite spatial extent. Model calculations predict that the dependence of the superelastic scattering intensity on the linear polarization direction of the laser beam can be severely distorted due to the existence of a finite scattering volume. Our measurements confirm the presence of this distortion and are well described by the model calculations. Conclusions are drawn concerning the influence of this effect on the extraction of electron-impact coherence parameters.

The HCl 2${\mathit{p}}_{\mathrm{Cl}}$→${\mathrm{\sigma }}^{\mathrm{*}}$ photoexcitation resonance has been studied using a tunable synchrotron radiation beam with a narrow bandwidth. Extensive ab initio molecular and atomic calculations have been carried out to analyze the details of the measured electron spectra. The interatomic potential-energy curves have been calculated for the ground and selected excited states of HCl using the complete-active-space self-consistent-field method. Multiconfiguration Dirac-Fock energies and line intensities of the atomic chlorine Auger spectrum have been used to identify the intense atomic spectral lines in the measured electron spectrum. Comparison between theory and experiment indicates fast neutral dissociation of the excited HCl molecules, followed by resonance Auger processes of the core-excited chlorine atoms. The atomic spectral lines are found to overlap with a strong background of broad structures, which sum up to 40% of the total intensity. This contribution has been addressed to the 2.9-eV potential well in our potential-energy curve of the excited HCl allowing for Franck-Condon transitions to bound vibrational states with a molecular nonradiative decay mode.

We extend our probabilistic model of quasielastic particle transport to include possible inelastic scatterings of the particles in the bulk of the studied media. We show that this extended model can be used to describe different types of experiments involving electrons that go through or are reflected by a plane-parallel layer deposited on a substrate. In particular, we reanalyze the experimental results of low-energy (≲10 eV) electron transmission through solid xenon and solid molecular nitrogen. This analysis shows that the extended model is consistent with the quasielastic one, but is more powerful since we can now determine both the elastic and inelastic electron mean free paths. The analysis allows one to study the threshold creation of excitons that can be observed at about 8.5 and 9.5 eV in solid xenon, and around 7.5 eV in solid molecular nitrogen.

An experiment was performed recently [Y. Zhu, A. Lezama, Q. Wu, and T. W. Mossberg (unpublished)] in which a two-level atom of transition frequency Ω was placed in a bichromatic laser field with frequencies Ω±δ, of sufficient intensity to produce dynamic Stark splitting. The observed fluorescence spectrum differed qualitatively in almost all its details from the well-known Mollow triplet [B. R. Mollow, Phys. Rev. 188, 1969 (1969)]. In this article, we use a dressed-atom model to explain the observed results.

We report results of an experimental study of Stark broadening and shift of analogous transitions of S ii, Cl iii, Ar iv, Cl ii, and Ar iii in plasma of a low-pressure pulsed arc. These results, together with other available experimental data, were used for investigation of Stark broadening and shift of analogous transition of isoelectronic ions. Results of modified semiempirical calculations are used for comparison.

Four even-parity atomic series corresponding to transitions from the 5s’[1/2${]}_1^0$ level to the ${(}^2$${\mathit{P}}_{3/2}^0$)np,nf levels of krypton have been observed, using a resonant multistep two-color photoionization method. The energies of 7p’[3/2${]}_1$, 7p’[1/2${]}_1$, 7p’[3/2${]}_2$, 7p’[1/2${]}_0$, np[1/2${]}_1$, np[3/2${]}_2$, np[1/2${]}_0$, and nf[3/2${]}_{1,2}$ levels are determined and the principal quantum numbers are calculated for n up to 45, 32, 49, and 44, respectively. Strong spectral irregularities in intensity and position are analyzed with the help of Lu-Fano diagrams and multichannel quantum defect theory in the case of the most intense 5s’[1/2${]}_1^0$→np[1/2${]}_0$ series. Density shift rates have the constant value of -7.4(2)×${10}^{\mathrm{-}19}$ ${\mathrm{cm}}^{\mathrm{-}1}$/${\mathrm{cm}}^{\mathrm{-}3}$ for the s’→p high-n series members, outside regions where irregularities are observed, in agreement with existing doped krypton data. A close agreement with the Fermi model is obtained for these high-n members of regular series. Departure from this agreement is found for members whose excited levels are mixed with 7p’ states. A clear relationship between the p∼p’ admixture and shift rate decrease, in regions of irregularities, is demonstrated.

Various characteristics of frequency-integrated intensities of secondary radiation components near the resonance excitation region have been calculated for a three-level system coupled with a reservoir using a stochastic model. It has been found that the spectral and temporal characteristics of the resonant second-order optical processes can be understood consistently by considering that Raman scattering results from the average value of the induced-dipole moment with respect to the energy fluctuation due to the system-reservoir interaction, while luminescence results from its deviation from the average value. A simple method to determine parameter values that characterize the excited-state dynamics in condensed phases from the secondary radiation data is also discussed.

Uniform semiclassical quantization conditions are obtained for a one-dimensional Hamiltonian possessing octahedral symmetry. The Hamiltonian describes the rotational dynamics of ${\mathrm{SF}}_6$, a system in which tunneling plays an important role. Quantization conditions are obtained for each symmetry class. These are shown to agree with previously obtained primitive quantization conditions in the small tunneling limit and to reproduce a characteristic periodicity in the symmetries labels. Quantum and semiclassical eigenvalues are computed numerically. Near the classical separatrix the uniform quantization provides orders of magnitude improvement in accuracy over primitive quantization. Our calculation is based on periodic orbit theory, modified here to include classically forbidden reflections and transmissions, and completes a study undertaken in a previous paper. The methods used may be generalized to other Hamiltonians and symmetry groups.

The spin-exchange rates due to binary collisions and due to the formation of van der Waals molecules between ${}_{}{}^{83}{}_{}{}^{}\mathrm{Kr}$ nuclei and optically pumped rubidium-metal vapor have been determined using a technique that relies on the simultaneous observation of frequency shifts of nuclear magnetic resonance lines of noble-gas atoms and corresponding frequency shifts of electron paramagnetic resonance lines of alkali-metal atoms. In contrast, earlier studies have relied on the observation of the spin-relaxation rate of either the alkali-metal atoms or the noble-gas atoms.

The Zeeman Hamiltonian for (spinless) hydrogen in a constant magnetic field is shown to be equivalent to a four-dimensional anisotropic anharmonic oscillator. Using this relation, Rayleigh-Schrödinger perturbation series expansions of both systems can be related to each other and analyzed in a unified way. Special emphasis is laid upon analytical estimates of their behavior in large orders of perturbation theory. Employing the path-integral approach, a new large-order formula is derived for the expansion of the ground-state energy of the oscillator system. With use of known Bender-Wu formulas for isotropic anharmonic oscillators, the major part of this calculation becomes straightforward. Combined with the new equivalence, this calculation represents the simplest path-integral derivation of large-order formulas for the Zeeman system.