Excitation of atomic hydrogen in initial quantum levels ${\mathit{n}}_{\mathit{i}}$=1,2,3 colliding with multiply charged ions with charge states q from 1 to 26 is investigated in the impact energy range 10 (keV/u)/${\mathit{n}}_{\mathit{i}}^2$–10 MeV/u, by means of the classical trajectory Monte Carlo, many-state atomic orbital close-coupling, and symmetric eikonal formalisms. This extensive compilation of theoretical calculations confirms the feasibility of an empirical scaling relation (σ/q vs E/q) proposed in previous works to reduce the excitation cross sections induced by multiply charged ions to a single universal curve. This scaling, together with the semiempirical formula derived by Lodge and co-workers [J. Phys. B 9, 239 (1976)] for proton projectiles, is found to provide reliable excitation cross sections for the one-electron collision system. Good agreement is obtained between theory and experiment for proton impact on H(1s) at impact energies above 10 keV.

The multiphoton excitation of an atom by a strong pulsed laser field creates a transient inversion of the pumped, excited level with respect to a lower-lying intermediate level. This results in a coupled time-and-distance traveling-wave situation appropriate for the growth of auxiliary radiation fields that are coupled to the excited, intermediate, and ground levels. Under certain circumstances these fields can suppress the multiphoton excitation process. The two-photon pumping of a ground ${}_{}{}^3{}_{}{}^{}$P level of O to the first excited ${}_{}{}^3{}_{}{}^{}$P level and ionization to the continuum by the same field are analyzed for the growth of amplified spontaneous emission and parametric four-wave mixing. A threshold growth condition is used to interpret the numerical solutions of the appropriate Maxwell-Bloch equations. A novel transition from exponential to linear growth of the parametric waves is observed in the calculations.

We propose new basis sets for linear algebraic variational calculations of transition amplitudes for quantum-mechanical scattering problems. These basis sets are hybrids of those that yield the Kohn variational principle (KVP) and those that yield the generalized Newton variational principle (GNVP) when substituted in Schlessinger’s stationary expression for the T operator. Trial calculations show that efficiencies almost as great as that of the GNVP and much greater than the KVP can be obtained even for basis sets with the majority of the members independent of energy.

The current best-fit tabulation of the optical absorption of aluminum is modified to include K-edge extended x-ray-absorption fine structure and other near-edge structures. The rationale used in choosing the most consistent K-edge data is discussed. Sum rules and comparisons with optical and electron-energy-loss experiments are used to check the consistency of the modifications to the absorption spectrum. The forward scattering factor is calculated from the modified spectrum and a significant difference in ${\mathit{f}}_1$(ω) is found between the original and the modified data sets near the K edge. This is largely due to resonant effects in the near-edge absorption structure of aluminum.

The widely used rigid-rotor approximation of low-energy electron-molecule scattering theory neglects completely the vibrational motion of the target. The errors this approximation introduces into calculated elastic and rotational-excitation cross sections are larger than other sources of imprecision in present state-of-the-art electron-molecule collision studies. We have applied an alternative to the rigid-rotor approximation: an extremely simple vibrational averaging of the interaction potential. This procedure reintroduces effects due to the zero-point vibrational motion without incurring in the solution of the Schrödinger equation computational demands beyond those of a rigid-rotor calculation. Tests on e-${\mathrm{H}}_2$ and e-${\mathrm{N}}_2$ scattering demonstrate the improved accuracy and computational efficiency that results from vibrational averaging.

Iodine atoms, produced by laser-induced dissociation of molecular iodine, have been photoexcited with synchrotron radiation in the region of the 4d-shell excitation. A strong resonance is observed below the 4d ionization threshold, which is assigned to the 4d→5p${(}^2$${\mathit{D}}_{5/2}$) transition. Photoelectron spectra reveal that the main decay of such an excited state is through direct autoionization into outer shells, especially into singlet states. Above the 5${\mathit{s}}^{\mathrm{-}1}$ threshold, numerous lines are observed, which cannot be understood in a single-particle framework. Indeed, ab initio calculations point out that the 5${\mathit{s}}^{\mathrm{-}1}$ configuration is strongly mixed with the 5${\mathit{p}}^3$${(}^2$P)5d and 5${\mathit{p}}^3$${(}^2$D)5d configurations, so that observed lines cannot be separated into main and satellite lines. Moreover, strong dynamic correlation effects are observed via a strong variation of the Auger decay rate with the kinetic energy of the Auger electron.

Based on the dielectric-function method, we have investigated the energy loss and straggling of heavy atoms with atomic number ${\mathit{Z}}_1$ passing through the degenerate electron gas at low velocities. The size parameter Λ of the electron cloud on the projectile is newly determined according to the statistical variational method by taking into account the static screening effect of conduction electrons. The analytical formulas obtained here have ${\mathit{Z}}_1$ dependences different from those of existing theories in spite of the same velocity dependence. It is found that the screening effect on Λ enlarges the electronic stopping of the media by a constant value regardless of ${\mathit{Z}}_1$. Numerical results show agreement with the trends of the available data.

A theoretical model is proposed to interpret the physical behavior of a thin oil film (∼1 μm) on a glass substrate initially used as an infrared holographic recording medium. It is found that this model is governed by a nonlinear differential equation involving a van der Waals retarded interaction, which was solved numerically. Experimental measurements show very good correlation with the solution of the theoretical model. The experimental technique together with the theoretical model are then proposed for the study of physicochemical properties of thin films.

The classical dynamics of an electron under the influence of a screened Coulomb potential around fast ions in solids is investigated. A transition from regular to chaotic motion as a function of the binding energy is observed. We discuss possible signatures of chaotic dynamics in the final-state distribution of foil-excited atoms.

An artificial-channels scattering method [M. Shapiro and G. G. Balint-Kurti, J. Chem. Phys. 71, 1461 (1979)] is used with a transformed Hamiltonian [R. E. Moss and I. A. Sadler, Molec. Phys. 66, 591 (1989)] to calculate the energies of vibration-rotation levels for the ground electronic state of ${\mathrm{HD}}^{+}$. All nonadiabatic effects, except for part of the coupling of rotational and electronic angular momenta, are accounted for. The results, which are for v=0–21, J=0,1, together with some other levels involved in observed transitions, are compared with previous calculations, particularly those of Wolniewicz and Poll [Molec. Phys. 59, 953 (1986)]. Inclusion of a correction to the energies of J≠0 levels to allow for the remaining contribution of Π electronic states permits comparison with experimental transition energies. The agreement is excellent.

We present the radiative lifetimes for series of bound excited states of neutral magnesium and beryllium derived from the transition probabilities calculated in a simple configuration-interaction procedure using a finite basis set constructed from B splines. Our calculated radiative lifetimes compare very well with the most accurate recent state-selected excitation measurements. In particular, our calculation has removed the discrepancy between earlier theoretical and experimental lifetimes for the first few Mg i 3snd ${}_{}{}^1{}_{}{}^{}$D states that are strongly affected by the configuration mixing from 3pp configuration series.

The formation of ${\mathrm{Xe}}^{2+}$ by decay of 4d hole states in xenon has been investigated by observing both the ${\mathit{N}}_{4,5}$OO normal Auger spectra and the resonantly excited spectra using synchrotron radiation and a new form of electron–electron coincidence spectroscopy involving a magnetic-bottle time-of-flight analyzer. Direct double Auger processes from the resonance populate all accessible states of ${\mathrm{Xe}}^{2+}$ while indirect processes via superexcited ${\mathrm{Xe}}^{+}$ levels populate ground and lower excited states of ${\mathrm{Xe}}^{2+}$ preferentially.

We investigate the interaction of molecular electronic states through nuclear motion in the presence of a homogeneous magnetic field. The different possibilities and effects of this interaction are classified according to the symmetries and the qualitative behavior of the diabatic energy curves. As a central result we show that conical intersections of electronic energy potential surfaces, which are in the field-free case common for polyatomic molecules, appear in the presence of a magnetic field already on the level of a diatomic molecule.

High-resolution laser spectroscopy is used to study the Stark effect in helium. The energies, widths, intensities, and shapes of resonances above the classical ionization threshold are measured for a wide range of electric field strengths. The high resolution of the lasers combined with careful design of the electric field plates allow accurate determination of the line-shape parameters, including linewidths and asymmetries accurate in the best cases to 6%. The WKB quantum-defect method is used to obtain detailed theoretical predictions for these Stark resonances with no adjustable parameters. Our study concentrates on the diabatic states of greatest slope arising from the zero-field n=32 and 40 manifolds in regions where these levels are fairly isolated and fit well to Fano profiles. In all cases, we obtain excellent agreement between experimental and theoretical line-shape parameters. A simpler autoionization model also reproduces the results, although less accurately.

A semiclassical theory of linear response, which can be regarded as a simplified version of the random-phase approximation, is applied to the study of photoabsorption in atoms. Analogous calculations performed long ago by Kirzhnitz and collaborators [Sov. Phys. Usp. 18, 649 (1975)] suggested the existence of collective plasmonlike states at very large energy in the excitation spectrum of heavy atoms. We find one solution of the semiclassical random-phase approximation equation that is similar to the collective solutions found by Kirzhnitz et al. However, our ‘‘collective’’ solution is qualitatively different from the plasma oscillation of a homogeneous electron gas. In fact, contrary to the plasma oscillation, which belongs to a strong coupling regime, our solution pertains to a regime of weak coupling. In our formulation of the semiclassical linear response theory, the electron angular momentum can be treated either as a continuous or discrete variable. When the angular momentum is treated as a discrete variable, the collective solution found here does not differ appreciably from other single-particle types of excitations. In the version in which the electron angular momentum is discretized, the present semiclassical theory of atomic response gives results that are in qualitative agreement with those of quantum theories.

A spectroscopic study on the nonresonant multiphoton ionization of magnesium atoms in a high-intensity laser field is reported. Both 0.532- and 1.06-μm radiation in the intensity regime of ${10}^{10}$–${10}^{13}$ W/${\mathrm{cm}}^2$ are used to produce both singly and doubly ionized magnesium ions. Mass and angularly resolved electron-energy analyses were used in an attempt to gain insight into the dominant mechanisms responsible for ionization. An analysis is presented for intensity- and frequency-dependent results, and electron angular distributions are reduced in terms of atomic parameters derivable from lowest-order perturbation theory. The results demonstrate the important influence that the details of the atomic structure have in describing the high-field nonresonant ionization of magnesium.

We have measured the linewidths of 35 different triplet Rydberg states of the ${\mathrm{H}}_2$ molecule with quantum numbers n=10–22, L=3, v=1, and R=0–4. An 18-eV electron beam excites a collimated ${\mathrm{H}}_2$ beam to the metastable c(2p${)}^3$${\mathrm{\Pi }}_{\mathit{u}}$ state. Stepwise excitation using two counterpropagating cw single-mode dye laser beams excites the metastable molecule first to an intermediate state [(3d${)}^3$Σ or (3d${)}^3$Π] and then to a triplet nf Rydberg state. The linewidths for the nf Rydberg states give the autoionization rates, which agree satisfactorily with the polarizability–quadrupole-moment long-range interaction model. We also have measured the transition frequencies between these states to an accuracy of 0.002 ${\mathrm{cm}}^{\mathrm{-}1}$. We use these measurements to derive the ionization potential of the metastable triplet state to an accuracy of 0.020 ${\mathrm{cm}}^{\mathrm{-}1}$ and the energy difference between the metastable and ground states of ${\mathrm{H}}_2$ to an accuracy of 0.025 ${\mathrm{cm}}^{\mathrm{-}1}$.

Two-laser optical pumping schemes show great promise for atom preparation since they can act as a nearly perfect state selector. This paper presents a new theoretical model to evaluate the pumping efficiency of two-laser pumping schemes, taking into account optical, ground and excited states hyperfine and Zeeman coherences, neighboring transitions, and fluctuating laser fields. The model is used to predict the optical pumping efficiency of two lasers with Lorentzian spectral profiles on a beam of cesium atoms. The particular laser intensities and linewidths that optimize the optical pumping efficiency and rate are calculated.

Propagation of optical pulses, both Gaussian and square in time, at an oblique angle to the interface separating two nonlinear self-focusing media, is studied numerically. The role of a finite-medium response in determining the reflection and transmission asymptotics of the pulse is established, and it is confirmed that, in the limit of a negligible Debye relaxation time, the equivalent particle theory for cw incident beams applies. Examples of spatially distributed multiplexing and demultiplexing of optical pulse trains illustrate the usefulness of the equivalent-particle picture in designing novel optical switching architectures.

The passage-time (PT) distribution associated with the switch on of a laser with an injected signal can be used to detect weak signals. We calculate the distribution function of such a distribution. Results for the mean PT interpolate between the limit of no injected signal and a simple logarithmic law for strong signals. It has a scaling form with a single important independent parameter. The variance of the distribution is more sensitive to the presence of the injected signal than the mean. Explicit formulas for the limit of sensitivity of the detection method and for the bandwidth resolution are given.