Molecular-structure calculations using the pseudopotential method have been performed on the (ArHe${)}^{8+}$ system. The cross section for single-electron capture in ${\mathrm{Ar}}^{8+}$+He collisions was calculated for energies from 20 eV to 10 keV/amu. The perturbed-stationary-state method [M. Kimura, H. Sato, and R. E. Olson, Phys. Rev. A 28, 2085 (1983)], modified to include electron translation factors appropriate to two-electron systems, was used. The total cross section is relatively energy independent with a value of approximately 2.5×${10}^{\mathrm{-}15}$ ${\mathrm{cm}}^2$. The n=4 level of ${\mathrm{Ar}}^{7+}$ is found to be preferentially populated, with the 4f level being dominant.

Cross sections for production of electrons and positive ions by proton impact on water vapor have been measured from 7–4000 keV by the transverse-field method.

A universal formula for the upper bound of the radiative lifetime of a hydrogenic level is found to be (3ħ ${}_{}{}^3{}_{}{}^{}$/2m${\alpha }^3$$Z^4$$e^4$)$n^3$(l${+(1/2))}^2$. When compared with the exact lifetimes, the expression is found to agree within 10%. For quasihydrogenic atoms and ions, experimental lifetimes are generally found to coincide with the upper bound values.

$M_4$,5${\mathrm{N}}_4$,5${\mathrm{N}}_4$,5 Auger transitions in open-shell atoms In and Sn are studied by comparing the calculated profiles with experimental free-atom spectra. In and Sn atoms have the ground-state electron configurations . . .4$d^{10}$5$s^2$5p and . . .4$d^{10}$5$s^2$5$p^2$, respectively. The usefulness of the applied theory to predict the fine structure, which is due to the coupling of the electrons in the 5p shell with the electrons involved in the Auger decay, is investigated in going from the closed-shell atom Cd to the open-shell atoms of In and Sn.

We report our final result on the Lamb-shift measurement in hydrogenlike phosphorous using the $2s_{\frac{1}{2}}-2\mathrm{}{p}_{\frac{3}{2}}$ laser-resonance method. From the measured value of the $2s_{\frac{1}{2}}-2\mathrm{}{p}_{\frac{3}{2}}$ energy splitting [539.60(20) THz, or 5555.8(2.0) Å] the Lamb shift $S$ is deduced in the framework of Erickson's and Mohr's calculations. $S_{\mathrm{expt}}^{\mathrm{E}}$ and $S_{\mathrm{expt}}^{\mathrm{M}}$ are the results of the subtraction of the measured $2s_{\frac{1}{2}}-2\mathrm{}{p}_{\frac{3}{2}}$ energy splitting and the fine structure calculated by the two authors, respectively. The results, $|S_{\mathrm{E}}-S_{\mathrm{expt}}^{\mathrm{E}}|=0.43\mathrm{}\pm 0.20$ THz and $|S_{\mathrm{M}}-S_{\mathrm{expt}}^{\mathrm{M}}|=0.12\mathrm{}\pm 0.20$ THz, indicate agreement with Mohr's theoretical approach ($S_{\mathrm{M}}$) and are more than two standard deviations from Erickson's calculations ($S_{\mathrm{E}}$). A general overview on the experimental techniques and results is given. The general trend of the presently available experimental results on Lamb-shift measurements are compared with Mohr's calculations.

K-shell binding energies in free atoms for B and C have been determined with high accuracy by recalibrating the projectile Auger spectra of Bisgaard, Bruch, Dahl, Fastrup, and Ro/dbro. These results are then compared with theoretical predictions based on the unrestricted Hartree-Fock self-consistent-field method and previous experimental data and theoretical results.

The production of ${\mathrm{Na}}^{+}$ and ${\mathrm{Na}}_2$${\mathrm{}}^{+}$ in sodium vapor irradiated by pulsed laser light in the D-line region of the spectrum has been studied by varying the laser power density and the wavelength. The data, which were acquired with an order-of-magnitude higher resolution than those in our previous experiments, support our earlier conclusion that ions formed at laser wavelengths close to, but not coincident with, the D lines result from three-photon resonance-enhanced ionization of ${\mathrm{Na}}_2$ molecules present in the vapor.

The intensities of hyper-Rayleigh and hyper-Raman scatterings are, already in the electric dipole approximation, shown to be different in right- and left-handed elliptically polarized incident light. The existence of this differential scattering requires the third-rank hyperpolarizability tensor $b_{\mathrm{ijk}}$ to be complex and j,k symmetric only.

It is proved that the imaginary part of the diagonal matrix element 〈Ψ‖(E-H-iΓ${)}^{\mathrm{-}1}$‖Ψ〉 of the Green’s function is the maximum of a variational functional. This provides convenient lower bounds. Upper bounds to the imaginary part are deduced with the aid of Padé approximants. Upper bounds of the real part of the transition amplitude are shown to follow from the unitarity relation. Finally, upper and lower bounds on nondiagonal matrix elements are derived and it is also shown that it is possible to obtain both upper and lower bounds on the real part of the transition amplitude. The negative consequence of employing these bounds is that we must deal with four-body operators.

We study the correlations and the isothermal compressibility of the Lennard-Jones fluid in the Percus-Yevick approximation in the critical region. The equation is solved numerically and the critical behavior is found similar to that for short-range forces: classical exponents but a nonclassical and nonuniversal scaling function that leads to an asymmetry between liquid and vapor with a true spinodal present only on the high-density side of the critical density.

Noninvertible one-dimensional maps with cycle periods undergoing multiplication by a factor N, as a result of (tangent) bifurcation, are governed by map-independent universal constants ${\alpha }_N$,${\delta }_N$ as the parameter λ of the map approaches the point of accumulation ${\lambda }_{N\infty }$. By explicit computation, we have determined the constants for all cycle structures and all values of N up to 7 (and in addition for many cycles up to N=11). We find that the relation between α and δ is roughly independent of the detailed cycle structure and follows quite well the Eckmann-Epstein-Wittwer asymptotic prediction that 3δ=2${\alpha }^2$. .AE

The most general low-frequency electrostatic plasma response to the high-frequency upper-hybrid oscillations is obtained. Accounting for the relativistic electron mass variation and the ponderomotive force nonlinearities, a pair of coupled nonlinear equations are derived. The latter describe the coupling of the high- and low-frequency potential oscillations in magnetized plasmas. Localized envelope wave packets are found in limiting cases. The importance of the relativistic mass variation nonlinearity is examined.

Periodic forcing provides a sensitive probe on the dynamics of the Lorenz system near the onset of chaos. The unstable limit cycle in the Lorenz system produced by Hopf bifurcation is found to stabilize beyond a critical amplitude of forcing. This extends the dynamical similarity of the Lorenz system to real hydrodynamics (unforced) up to the onset of turbulence. We study the routes to chaos in this forced system.

The solution of a general one-dimensional correlated random walk with arbitrary initial and boundary conditions is obtained, and used to derive the asymptotic return probability in the presence of a random distribution of traps. The effect of correlation is shown to be equivalent to scaling time in the ratio of the forward- and backward-scattering probabilities.

Multiphoton ionization of cesium atoms shows pronounced two-photon resonances at the nd states and, to a much smaller extent, at the ns states. A dc electric field augments the ns resonances and, for a complementary reason, induces resonances at the np and nf levels. A scaling law for field-induced signals, as a function of principal quantum number, is reported. Field ionization of high Rydberg states is also conveniently studied and quantified with our technique.

Three new progressions consisting of broad bands (full width at half maximum ≃130 meV) have been observed in the absorption spectrum of NO trapped in an argon matrix. A Wannier model fails to describe these transitions: they are identified as the molecular Rydberg transitions A ${}^2$${\Sigma }^{+}$, C ${}^2$Π, and D ${}^2$${\Sigma }^{+}$-X ${}^2$Π(v’,0), blue shifted with respect to their gas-phase positions by about 0.85 eV.

We report the first observation of electric-field-induced resonances in the multistep photoionization of hydrogen. Asymmetric profiles having blue wings are observed near the photoionization limit resulting from tunneling across the Stark-Coulomb combined potential (shape resonance). We measured the dependence of the spacing of the resonances on the electric field strength.

We derive general expressions for the efficiency of cw phase conjugation by degenerate four-wave mixing and for the power $P_{\mathrm{cr}}$ for cw self-trapping of coherent electromagnetic beams in fluids and glasses in which these effects arise predominantly from driven nuclear motions (molecular vibrations, molecular reorientation, elastic deformations, etc.). Apart from their dependence on beam frequency ω, medium temperature T, and refractive index n, these expressions are functions only of the integrated (polarized and depolarized) light scattering strengths versus scattering angle in the medium and the attenuation coefficient α. There is no other dependence on the scattering mechanism. When attenuation is entirely due to scattering, the expressions simplify and suggest that unprecedented low powers (in the microwatt regime for microwaves) can produce self-focusing and strong phase conjugation, as well as other beam mixing effects, when beam geometries are optimized in the scattering medium. In this case we find, for example, $P_{\mathrm{cr}}$∼${\mathrm{nk}}_B$T${\omega }^2$/cα (${\mathrm{k}}_{\mathrm{B}}$ is Boltzmann’s constant and c is the velocity of light) provided that there is significant beam diffraction in length ${\alpha }^{\mathrm{-}1}$. Our results also apply to some other media such as electron plasma.

The average molecular orientation of a monolayer of sodium-dodecylnaphthalene-sulfonate on a water-air interface has been determined by use of optical second-harmonic generation. The molecular orientation is shown to vary smoothly with increasing surface density of the molecules.

Exact solutions to the nonlinear Rayleigh-Taylor instability in nonuniform acceleration fields are discussed. They demonstrate the dependence on increasing as well as decreasing acceleration and give accurate theoretical estimates for uniform acceleration which confirm the results of previous vortex simulations and conformal mapping methods.