Many-body perturbation theory has been used to calculate photoionization cross sections with excitation of neutral argon leaving the ion in $3s^{2}3p^4\left({}_{}{}^1{}_{}{}^{}D\right)md\left({}_{}{}^2{}_{}{}^{}S\right)$ levels. Correlations both in the final state and ground state are included. Calculated cross sections for $3s^{2}3p^6\to 3s3p^6\epsilon p$ and $3s^{3}3p^6\to 3s^{2}3p^4\left({}_{}{}^1{}_{}{}^{}D\right)md\left({}_{}{}^2{}_{}{}^{}S\right)\epsilon p$ excitations were used to determine the satellite intensities, which are compared with photoelectron measurements and other calculations.

Rotationally selective photoionization dynamics for the transition $\left(\mathrm{N}{\mathrm{O}}^{+}\right)X{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}(v^{+}=0, N^{+})\leftarrow \left(\mathrm{NO}\right)A{}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}(v=0, N_A, J_A=N_A+\frac{1}{2})$ is studied by high-resolution zero-kinetic-energy photo-electron spectroscopy (ZEKE-PES). Two-photon, two-color photoionization via the NO $A$ state in a skimmed supersonic jet is employed in the experiments. The observed angular momentum transfer ion←molecule is found to depend strongly on the initial quantum number $N_A$. The ionization potential is determined to be 74719.0±0.5 ${\mathrm{cm}}^{-1\mathrm{}}$.

The long lifetime of photons in a high-$Q$ micromaser cavity is used to generate a $|n〉$-state maser field by injecting atoms, one at a time. Every atom is probed for its excitation after leaving the cavity so that the precise number of photons in the field is known. We calculate the probability of obtaining $n$ photons after $m$ atoms have passed the cavity.

We consider the formation of viscous fingers in porous media using the boundary-integral method with particular application to a recent experiment involving a Hele-Shaw cell filled with glass beads. When the less viscous fluid wets the beads we can account for the patterns as ordinary viscous fingers in the presence of large noise.

The phase diagram of growing crystal patterns for succinonitrile is obtained experimentally in a supercooling-anisotropy phase space. The anisotropy of the crystal growth is changed by roughening the upper surface of the bottom plate of the thin crystal-growth cell. Various growing modes are observed, and the relation between regular dendritic and random diffusion-limited-aggregation-like crystals is discussed.

We prove that the center of mass of a sine-Gordon kink in contact with a thermal reservoir approaches equilibrium by undergoing a Brownian motion in the limit that $k_{B}T\ll E_k$ where $E_k$ is the rest energy of the kink. Our method consists of introducing a collective variable Hamiltonian for the kink system in which the center of mass of the kink is a canonical variable. Next we use standard projection-operator techniques to derive the equation of motion of the distribution function of the center of mass of the kink. Then we show that in the limit $k_{B}T\ll E_k$ the distribution function satisfies the Fokker-Planck equation of Brownian motion.

It is predicted and confirmed numerically that the nonlinear stationary waves on the surface polariton branch of a thin-film dielectric waveguide are unstable to transverse spatial fluctuations in the dimension parallel to the confining layers. Bounded waves whose peaks are located within the linear thin-film guiding layer show behavior in qualitative agreement with that of earlier studies on the two-dimensional propagation problem.

A probabilistic model is used to determine the spectrum of scaling indices for the cross section of a strange attractor embedded in two-dimensional maps. The cross section is modeled by a probabilistic Cantor set. An ensemble of partitions is averaged to construct a mean partition function $\mathcal{G}$ called the genealogy. Solving the genealogical equation $\mathcal{G}=1\mathrm{}$ determines $f-\alpha$ pairs, and thus the $f\left(\alpha \right)$ spectrum. The Zaslavskii and Hénon maps are used as examples. The results of the calculation are smooth spectra.

We have identified a contribution to the ring current magnetic susceptibility of icosahedral ${\mathrm{C}}_{60}$ which diverges paramagnetically as the relative strengths of the two inequivalent bonds of this molecule are varied. This divergence is invoked to explain the near cancellation of the diamagnetism generally expected of aromatic hydrocarbons.

A nonvariational parameter-free molecularlike approach is developed for the three-body problem based on the Faddeev equations. Considering a system of two identical heavy particles (atomic nuclei) and a light one (electron), we study the adiabatic limit of the corresponding Faddeev equation in the absence of interaction between the heavy particles and using general heavy-light potentials that are represented in a separable form through the Hilbert-Schmidt method. The resulting rotationally invariant Faddeev two-center eigenfunctions are used to formulate an ansatz for the solution of the full Hamiltonian where all three particles interact. A set of coupled differential Born-Oppenheimer-like equations is obtained for the movement of the heavy particles. Numerical calculations are shown for the 1sσg, 2sσg, 3dσg, 2pσu, and 2pπu electronic states in ${\mathrm{H}}_2$${\mathrm{}}^{+}$. The resulting molecular energy curves appear to converge to the exact ones when up to fifteen terms are used in the Hilbert-Schmidt expansion of the Coulomb potential. The noncrossing rule for 2sσg and 3dσg curves is verified in our work.

The quantum traversal time $t_{\Omega }$ is obtained as a matrix element of the classical functional in Feynman path-integral technique. The properties of $t_{\Omega }$ and its relation to the observables in scattering experiments are investigated. The general expression for the tunneling time is found in the one-dimensional case. Various traversal times of previous works are shown to be simply related to $t_{\Omega }$ as Re$t_{\Omega }$, Im$t_{\Omega }$, or ‖$t_{\Omega }$‖. Other possible constructions of time parameters describing the motion of a quantum particle are discussed.

Symmetrized Trotter approximations to $e^{\mathrm{-}\beta H}$ are employed to compute the low-energy eigenstates of a two-level system linearly coupled to a harmonic oscillator. At high coupling strengths the ground state is nearly doubly degenerate and the projectors become very inefficient. It is demonstrated that the projection technique in combination with the variational principle yields a new efficient method to calculate simultaneously all nearly degenerate eigenvalues and eigenstates. The dynamic properties of the system in the ground state are studied by evaluating the time- and frequency-dependent correlation functions. Depending on the ratio of the tunneling frequency relative to the oscillator frequency, the system behaves differently under increasing coupling strength.

The behavior of projectile electron capture and ionization cross sections at ultrarelativistic energies (>10 GeV/amu) is discussed. Three mechanisms contribute to electron capture at these energies: radiative and nonradiative capture and the capture of the electron following electron-positron pair production. The radiative and nonradiative cross sections both fall off as ${\gamma }^{\mathrm{-}1}$ at high energies, (γ-1)${\mathrm{Mc}}^2$ being the ion energy. The vacuum capture cross sections increase as the lnγ. Projectile 1s ionization cross sections also increase as lnγ at high energies if target screening is negligible. However, when the projectile atomic number is smaller than the target atomic number, the transverse interaction giving the lnγ term is screened and reduced. Therefore, the total 1s ionization cross sections are dominated by Coulomb ionization, and are nearly constant with increasing projectile energy. Tables of reduced capture and ionization cross sections are given, and are applied to calculating the charge states of ions in matter and the lifetime of ions in storage rings.

Positron-${\mathrm{CH}}_4$ (and position-${\mathrm{SiH}}_4$) are studied at low collision energies (E<10 eV) by employing a parameter-free model potential constructed within the one-center-expansion formalism of the full interaction. The obtained potential is in turn employed in a close-coupling treatment of the quantum-mechanical scattering equations that are solved within the fixed-nuclei approximation to yield the full K matrix. The all-important polarization of the target plays here a fundamental role in generating the final elastic integral cross sections below the threshold of the positronium formation, where the present results can be compared with the available experimental data and with other theoretical predictions.

Alignment and orientation for H(2p) excitation in ${\mathrm{H}}^{+}$-He collisions have been measured for incident proton energies of 1–4 keV, and scattering angles between 0.5° and 3.5°. From the results the relative population of magnetic substates H(2$p_0$) and H(2$p_{\pm 1}$) (i.e., the differential alignment and orientation) is extracted. The results are in excellent agreement with recent theoretical calculations. The observed magnitude of H(2$p_0$) excitation demonstrates that, in addition to a 2pσ-2pπ rotational coupling, a 2pσ-2sσ radial coupling is effective at small impact parameters.

An equivalent operator Λ̃ removing the Coulomb degeneracy in the second order of perturbation theory for the two-center problem in the limit of separated atoms is found. Eigenvalues and eigenfunctions of the operator Λ̃ allow us to construct a complete classification of states of the two-center problem in appropriate coordinates, a compatible adiabatic basis (CAB). Averaging of the total Hamiltonian of a three-body problem over CAB results in a system of adiabatic equations in slow variable scrR, the hyperradius of the three-body problem. It is shown that asymptotics of that system of equations is compatible with physical boundary conditions of the scattering problem.

The Feshbach formalism is employed in investigations of the effects of interacting and/or overlapping resonances on dielectronic recombination. Model systems are considered, and the problem of singly charged target ions is discussed. Small reductions in dielectronic recombination cross sections are found to occur for these systems. Comparison is made with the results of multichannel quantum-defect theory calculations.

The energy loss for protons on Al, Cu, and Ag thin foils around the maximum of the stopping have been measured at two different exit angles. The bombardment energy $E_{\max }$ where such a maximum occurs is found to depend on the angle of observation, $E_{\max }$ being greater when the detector is positioned off beam than when measured downstream in the beam direction. These results are discussed in terms of a varying participation of different electrons in the target. The effect of foil inhomogeneities on $E_{\max }$ is also evaluated.

An analytical method is proposed to determine absolute total cross sections per scatterer and related mean free paths for low-energy electron scattering in disordered molecular solid films. The procedure is based on a two-stream multiple-scattering model of the thickness dependence of the film reflectivity for elastic electrons. The expected analytical behavior and accuracy are tested on a model sample whose scattering properties are generated by a Monte Carlo simulation from initially known parameters. The effects of multiple scattering inside the film and at its interfaces are taken into account and discussed. The thickness dependence of the elastic electron reflectivity of ${\mathrm{H}}_2$O film condensed at 14 K is reported between 1 and 20 eV incident energy with a spectrometer resolution of 10 meV. The proposed method is applied to extract from these measurements the energy dependence of the total effective and total inelastic cross sections for electron scattering in amorphous ice.

High-resolution vibrational electron-energy-loss spectra of amorphous ice films condensed at 14 K are reported for the incident-energy range 1–18 eV. Absolute electron scattering cross sections for elastic collisions, individual vibrational excitations, and the sum of electronic transitions are obtained by performing a two-stream multiple-scattering analysis of the spectra. The various features found in the energy-dependent cross sections are discussed, whenever possible, by comparison with data and mechanisms (e.g., transient anion formation) well established in the gas phase. Quantum-interference effects introduced implicitly in the cross sections by the classical analysis are discussed within the first Born approximation for electron–multiple-site scattering.