Using the theory of ideal quantum measurements as a basis, we show that the atomic state measurement has a great effect on squeezing of the field in the Jaynes-Cummings model.

We consider the Rayleigh-Taylor instability in exponential density profiles and derive two approximate expressions for the growth rate that are explicit and involve only the Atwood number A and the wave number k. Our results agree with the exact growth rate within 6–12 %. We also point out that a recently published expression deviates from the exact growth rate for practically all values of A and k [M. H. Emery, J. P. Dahlburg, and J. H. Gardner, Phys. Fluids 31, 1007 (1988)].

Intensive Monte Carlo simulations are performed to calculate the reaction kernel for diffusion-limited chain-chain aggregation in three dimensions. The numerical data are in agreement with the mean-field Smoluchowski theory and the conjectured overall form of the reaction kernel is confirmed.

The random sequential adsorption of ellipses on a uniform flat surface is studied using simulation methods. Contrary to expectations, the usual asymptotic law for the coverage versus time: Θ(∞)-Θ(t)=${\mathrm{kt}}^{\mathrm{-}p}$, with p=(1/2 is not obeyed. The long-time behavior is still well described by a power law. However, the effective parameter p is always less than (1/2 and decreases as the elongation of the ellipse increases: It is close to (1/3 for weakly elongated ellipses, while it approaches (1/4 for a system of ellipses with axial ratio 5.

The mean time taken for the degenerate parametric oscillator to quantum tunnel between its two above-threshold stable states is calculated in the large photon-number limit. The result is compared with an earlier approximate result using a truncated Fokker-Planck equation in the Wigner representation. This earlier theory is equivalent to stochastic electrodynamics. Our quantum theory results indicate orders of magnitude faster tunneling far above threshold, when compared to the truncated Wigner theory.

Stratified continuum percolation is a percolation model based upon self-similarity that can describe correlated transport and connectivity problems. It is demonstrated that this construction of correlated percolation retains some of the properties of random percolation. Most importantly, the critical threshold remains well defined, independent of changing correlations. These results introduce a new approach to understanding correlated flow systems.

A simple irreversible kinetic model recently introduced by Ziff, Gulari, and Barshad [Phys. Rev. Lett. 56, 2553 (1986)] to describe the catalysis of chemical reactions on regular surfaces has been shown to have a second-order phase transition from an absorbing state, wherein the surface is passivated (rendered catalytically inactive or ‘‘poisoned’’) by one of the chemical constituents, to an active steady state. We argue here that this transition belongs in the universality class of Reggeon field theory, i.e., of directed percolation.

Nuclear physics experiments being constructed will create narrow beams of particles repelling each other with Coulomb forces but effectively attracted to a central axis, and cooled to such temperatures that they are expected to crystallize. A numerical search for ground states finds that particles lie within narrow shells, and within each shell on paths that twist about the central axis like lines around a barber pole. The system possesses an infinite set of ordered local-energy minima, and is probably a glass.

Valence removal energies, hyperfine constants, and E1 transition amplitudes are calculated for the 2$s_{1/2}$, 2$p_{1/2}$, 2$p_{3/2}$, and 3$s_{1/2}$ states of Li and ${\mathrm{Be}}^{+}$. This calculation is an extension of earlier second- and third-order many-body perturbation theory (MBPT) calculations, in which now an infinite subset of MBPT terms is evaluated using all-order methods. Agreement with experiment at the 0.01% level for energies, and at the 0.1% level for matrix elements, is found. Issues involved with those higher-order terms omitted by the technique are discussed.

The O(4) supermultiplets of doubly excited states of atoms are analyzed and reexpressed in a generator-coordinate representation. It is explicitly shown that a complete separation of the collective and internal motions is realized in the high-excitation limit. A new explicit expression for the collective vibration in terms of quasispin operators is also derived. Particular emphasis is put on the close relation between the group-theoretical supermultiplet classification and the mean-field theoretical approach.

The unusual autodetachment spectrum of metastable ${\mathrm{He}}_2^{\mathrm{-}}$ is studied theoretically, using high-level coupled-cluster methods and hybrid numerical and Slater orbital basis sets. By obtaining accurate curves for the repulsive wall of the ground ${\mathrm{He}}_2$(X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$) state, the excited ${\mathrm{He}}_2$(a ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$) state, and the metastable ${\mathrm{He}}_2^{\mathrm{-}}$${(}^4$${\mathrm{\Pi }}_{\mathrm{g}}$) state, we are able to provide an alternative explanation for the experimental observations, which had cast doubt on the veracity of the accepted curve for the repulsive part of the ${\mathrm{He}}_2$(${\mathrm{X}}^1$${\mathrm{\Sigma }}_{\mathrm{g}}^{+}$) potential. We attribute the experimental peak at 15.78±0.13 eV to transitions of vibrationally excited states (ν=2 and higher) of ${\mathrm{He}}_2^{\mathrm{-}}$ to the ${\mathrm{He}}_2$(X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$) continuum, since the v=0 transition would have a value 1 eV less. An error of this size is considered to be far outside the error bars for highly accurate correlated ab initio calculations. The electron affinity of the ${}_{}{}^4{}_{}{}^{}\mathrm{\Pi }_{\mathrm{g}}^{}{}_{}{}^{}$ state of the anion (measured relative to a ${}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$) is computed to be 0.201 and 0.212 eV for different basis sets, compared to an experimental value of 0.175±0.032 eV.

A relativistic self-consistent-field self-interaction-corrected local-spin-density functional, with electronic correlation included, has been used to compute the electronegativities of monatomic systems with nonintegral nuclear charges. We focused specifically upon quark atoms related to the halogens, having nuclear charges of Z±1/3. Two different methods for calculating electronegativities were found to give results in good agreement with each other and with an earlier empirical approach. It was also shown that accurate energy and electronegativity differences for the isoelectronic quark-atom pairs Z+1/3,Z-1/3 and Z+2/3,Z-2/3 can be determined using only the electrostatic potentials at the nuclei of the isoelectronic atoms and ions with integral nuclear charges.

Using multiconfiguration linear-response theory, accurate predictions are given for the static and dynamic dipole polarizabilities of ${\mathrm{Li}}^{\mathrm{-}}$. Benchmark full configuration-interaction (CI) results are also presented. Virtually exact full CI results are obtained for a very compact wave function keeping 1s doubly occupied and describing the correlated movement of the remaining two electrons with three orbitals: 2s, 3s, and 2p. d functions are found to be crucial for the calculation of the dipole polarizability and for obtaining gauge invariance. The static polarizability is predicted to be 798±5 a.u.

A generalized Heitler formalism is used to unify the description of various subtraction schemes that have appeared in the literature for calculating two-body off-shell amplitudes in terms of the solution Γ of an auxiliary nonsingular integral equation. This leads to a universal representation of the off-shell transition matrix for both positive and negative energies in terms of any one of a very general class of Γ matrices.

The room-temperature, binary, collision-induced, translational, and rotational spectra of molecular hydrogen are reported. The translational pair spectrum is separated into completely depolarized and polarized components; both are analyzed with quantum line-shape calculations based on the isotropic potential approximation and the dipole-induced-dipole (DID) model for the pair polarizability. A small overlap correction to the DID anisotropy yields a computed line shape that agrees with the observed depolarized, collision-induced spectrum. A substantial overlap correction to the DID trace is needed to produce a line shape consistent with the measurement of the collision-induced trace spectrum. Additionally, this modified DID trace reproduces the experimental data on the second dielectric virial coefficient.

We propose a simple model to incorporate inelastic energy losses into molecular-dynamics simulations of high-energy radiation damage, which at the same time describes the metallic thermal conductivity by coupling the ions to a thermal reservoir. Both expressions are based on a local-density description of stopping power. We provide an empirical expression to describe the strength of the ion-electron coupling, which is a function of the local electronic density. The model is then adequate to those simulations where the ion-ion interactions are obtained from many-body potentials based on density-functional formalism.

Rate coefficients for electron-impact excitation have been calculated for transitions from the ground state to n=3 excited states of six neonlike ions with atomic numbers Z=15, 17, 26, 34, 42, and 54. The direct-excitation rate coefficients were calculated using relativistic multiconfiguration target wave functions and a relativistic distorted-wave approximation. The contributions from autoionizing resonances were evaluated using a multiconfiguration Dirac-Fock model. These resonances enhance the rate coefficients for transitions to the 2$p^5$3s states by as much as a factor of 3. The peak rate coefficient and the relative importance of resonance excitation diminish with increasing atomic number. However, we find that resonance enhancements are generally quite large for electron temperatures less than the temperature where peak excitation occurs. Our total rate coefficients for ${\mathrm{Se}}^{24+}$ are in good agreement with close-coupling results obtained with R-matrix calculations. The resonance contributions from the present work differ from the results by Smith et al. [Astrophys. J. 298, 898 (1985)] for the ${\mathrm{Fe}}^{16+}$ ion by as much as a factor of 3–5.

The energy transfer between a pair of excited Na(3p) atoms leading to Na(3s)+Na(5s) and Na(3s)+Na(4d) final states is studied in a semiclassical coupled-state theory. Classical trajectories are evaluated from the average adiabatic potentials of previously calculated excited molecular states of ${\mathrm{Na}}_2$. With this specification of average nuclear R(t) for atoms approaching in a given magnetic quantum number ($m_a$,$m_b$) substate, we solve the coupled equations for the time-dependent Schrödinger equation in the 21-state diabatic basis set (including 3p, 3s, 5s, and 4d) of atom pairs. The coupling terms arise from the dipole-dipole interaction. Excellent agreement is obtained with the data of the two most recent measurements of the 3s+4d and 3s+5s energy-transfer cross sections at T∼500–600 K. Extension to low temperature shows a rising 3s+5s cross section as a result of a net attractive adiabatic potential in the ($m_a$,$m_b$)=(1,0) incident channel, as also occurs for associative ionization.

We derive simple and exact expressions for the leading quantum corrections to the angular and energy distributions of an atom scattered inelastically from a solid crystalline surface. The quantum corrections are given in terms of classical trajectories and equilibrium correlation functions for the solid surface. Our results are useful when the incident atom has an energy of ∼1 eV and the surface has a temperature less than or comparable to the Debye temperature.