Theoretical studies are reported of total and partial-channel photoexcitation and ionization cross sections in carbon dioxide. As in previously reported studies of discrete and continuum dipole spectra in diatomic (${\mathrm{N}}_2$, CO, ${\mathrm{O}}_2$, ${\mathrm{F}}_2$) and polyatomic (${\mathrm{H}}_2$O, ${\mathrm{H}}_2$CO, ${\mathrm{O}}_3$) molecules in this series, separated-channel static-exchange calculations of vertical-electronic transition energies and oscillator strengths and Stieltjes-Tchebycheff moment methods are employed in the development. Detailed comparisons are made of the static-exchange excitation and ionization spectra with photoabsorption, electron-impact excitation, and quantum-defect estimates of discrete transition energies and intensities, and with partial-channel photoionization cross sections obtained from fluorescence measurements and from tunable-source and ($e$,$2e$) photoelectron spectroscopy. The spectral characteristics of the various discrete series and continua are interpreted in terms of contributions from compact $2{\pi }_u\left({\pi }^{*}\right)$, $5{\sigma }_g\left({\sigma }^{*}\right)$, and $4{\sigma }_u\left({\sigma }^{*}\right)$ virtual valence orbitals, and from more diffuse discrete and continuum Rydberg orbitals. The $2{\pi }_u\left({\pi }^{*}\right)$ orbital is found to contribute to discrete excitation series, whereas the $5{\sigma }_g\left({\sigma }^{*}\right)$ and $4{\sigma }_u\left({\sigma }^{*}\right)$ orbitals generally appear in the photoionization continua as resonancelike diabatic valence features. Good agreement obtains between the calculated discrete excitation series and the results of a recent analysis of the available spectroscopic data. The calculated outer-valence-shell $\left(1\mathrm{}{\pi }_g^{-1\mathrm{}}\right)X{}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$, $\left(1\mathrm{}{\pi }_u^{-1\mathrm{}}\right)A{}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$, $\left(3\mathrm{}{\sigma }_u^{-1\mathrm{}}\right)B{}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$, and $\left(4\mathrm{}{\sigma }_g^{-1\mathrm{}}\right)C{}_{}{}^2{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ partial-channel photoionization cross sections are in good accord with measured values, and clarify completely the origins of the various structures in the observed spectra. There is evidence, however, of coupling among scattering states associated with $1{\pi }_g^{-1\mathrm{}}$ and $1{\pi }_u^{-1\mathrm{}}$ ionic channels, giving rise to moderate disagreement with tunable-source photoelectron and fluorescence measurements over a portion of the spectrum. In the inner-valence-shell region, the calculated $2{\sigma }_u^{-1\mathrm{}}$ and $3{\sigma }_g^{-1\mathrm{}}$ cross sections are in qualitative accord with the observed many-electron spectral intensities, and provide a basis for quantitative interpretation when combined with appropriate intensity-borrowing calculations. The calculated carbon and oxygen $K$-edge cross sections are in good agreement with available cross sections obtained from electron-impact and photoabsorption measurements. It is of particular interest to find the oxygen $K$-edge ($1{\sigma }_g^{-1\mathrm{}}$, $1{\sigma }_u^{-1\mathrm{}}$) cross section exhibits both the expected $5{\sigma }_g\left({\sigma }^{*}\right)$ and $4{\sigma }_u\left({\sigma }^{*}\right)$ resonancelike features. Finally, comparisons are made throughout of the discrete and continuum spectra in carbon dioxide with the results of previously reported studies in CO and ${\mathrm{O}}_2$, and the origins of the similarities and differences in the cross sections in these cases are clarified.

We describe the temporal behavior of the dynamic elements of an exactly soluble quantum model. The model consists of a single two-level atom or spin interacting with a single mode of the quantized radiation field in the dipole approximation, the mode being initially in an arbitrary coherent state of excitation. We give new long-time numerical and closed-form approximate analytic solutions for the expectation values of the atomic dipole moment and the difference in population of the two atomic levels in the rotating wave approximation. The atomic dipole-dipole correlation function is calculated. All of the results are obtained without semiclassical or decorrelation approximations. Unusual features found in the temporal behavior of this lossless model problem are "collapse," i.e., episodic nonexponential damping of both the atomic inversion and dipole moment, and two kinds of "revival" or partial recorrelation, in the dynamic evolution, during which the initial state is nearly recovered. We give analytic formulas for the collapse function, for both of the revival times, and for the envelope of the revival maxima. Some remarks are made about the nature of irreversibility in this exactly soluble and loss-free model.

Continuum x rays from targets of Be, C, and Al bombarded with 6-40-MeV protons were observed with a Si(Li) detector. In addition to the secondary-electron bremsstrahlung (SEB), the spectra show another component, of which the high-energy limit is given by the relative kinetic energy between the projectile and orbital electrons of the target atom and by the Doppler effect. The component can well be explained in terms of the bremsstrahlung produced by the quasifree scattering of orbital electrons in the field of the projectile. The effect of the binding energy of the orbital electrons on this bremsstrahlung spectrum has been studied. From the comparison of the experimental results with theoretical predictions based on the plane-wave Born approximation and the binary-encounter approximation, the importance of the effect of secondary-electron escape from the target material on the SEB at high-projectile energies was pointed out.

Under some conditions many types of laser oscillators are known to produce their output in the form of an infinite periodic pulse train, even when the pump rate and cavity losses are independent of time. For some lasers the underlying cause of the instability is well understood, while for others the source of pulsations remains unknown. Emphasis here is on a coherent pulsation effect which previously has only been analyzed in relation to Doppler-broadened gas lasers. The same effect is shown to apply also to lasers with non-Doppler line broadening and the governing stability criteria are derived.

Excess electrons in dense ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ gas are known to become self-trapped if the gas density exceeds a certain temperature-dependent value ${\rho }_1\mathrm{}\left(T\right)\mathrm{}$. At this density, the electron mobility falls sharply, forming a first mobility edge. For the ranges of densities and temperatures over which this behavior has been observed, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ gas is an almost ideal easily deformable system; conditions which favor the formation of the self-trapped state. However, with isothermal increase in density beyond ${\rho }_1\mathrm{}\left(T\right)\mathrm{}$, the gas becomes stiffer as repulsive atom-atom interactions predominate. A lattice-gas model for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ predicts a second density ${\rho }_2>{\rho }_1$ at which the low-mobility localized state becomes unstable, decays into a nonlocalized electron state, and the mobility sharply rises forming a second mobility edge.

For a system in a nonequilibrium macrostate we may distinguish four classes of microstates: Microstates which evolve toward the equilibrium state in the forward-time direction but away from the equilibrium state in the backward-time direction, microstates which evolve away from the equilibrium state in the forward-time direction but toward the equilibrium state in the backward-time direction, microstates which evolve away from the equilibrium state in both time directions, and microstates which evolve toward the equilibrium state in both time directions. A simple system is examined, and the fraction of each of the four classes is determined. It is shown that in the thermodynamic limit all the states belong to the last of the four classes. It is also shown that a system evolving toward the equilibrium state will, with overwhelming probability, continue to evolve toward the equilibrium state.

Ultrasonic shear data along the critical isochore in xenon and in the binary mixture nitrobenzene-$n$-hexane are interpreted in terms of modified theoretical expressions derived within the framework of the decoupled-mode theory. The new expressions mainly arise from separating the real and imaginary parts from the complex dynamic shear viscosity near a critical point. Numerical analysis of the data shows rather satisfactory agreement between theory and experiments for ultrasonic shear data.

We consider light scattering from nonequilibrium steady states (NESS) where both density fluctuations (already studied by others) and orientational fluctuations are important scattering mechanisms. When orientational fluctuations are important, the possibilities for new NESS scattering experiments seem to multiply considerably. A theory is given for two promising new experiments: VH (vertical-horizontal) scattering in the presence of a sound wave and VH-VV (vertical-horizontal-vertical-vertical) interference, which vanishes identically in equilibrium.

Localized excess-electron states are investigated using the density-functional formalism previously developed by Ebner, Saam, and Stroud for nonuniform classical fluids. The electron-atom interactions used contain a short-range effective core repulsion and a long-range polarization attraction. The interatomic interaction is a 6-12 potential. Some results are in agreement with previous density-functional calculations by Ebner and Punyanitya, who use a contact potential for the electron-atom interaction, in that no localized states are found in dilute helium and neon gases, while localized states are found in dense helium gas and liquid neon close to the liquid-gas coexistence curve. However, our present calculations disagree with the earlier ones in that they predict the localized states in liquid neon to be stable even at pressures much larger than the saturated vapor pressure, a consequence, we believe, of our inclusion of the polarization potential in the electron-atom interaction. We also find that localized states in the form of short-lived droplets are possible in argon and xenon gases close to the critical point. This finding is consistent with recent observations by Freeman and Huang of electron mobilities in these gases.

We present a method for generalizing the traditional two-term Legendre expansion solution of the Boltzmann equation in the context of electron swarm experiment analysis. The method is applied to the calculation of the distribution function and transport coefficients in ${\mathrm{N}}_2$ and in two model cases. We find that the two-term approximation is of limited validity for the cases considered here, and that four to eight terms in the Legendre series are required for convergence of the transport coefficients to the accuracy required for the determination of cross sections from swarm experiments.

Using material parameters determined by bulk behavior, and the lattice model presented previously by us [Phys. Rev. A 21, 1687 (1980)], we study interfacial and thin-film phenomena in the mean-field approximation. The effects of free and solid surfaces on orientational ordering for the isotropic phase are found to depend on the details of the intermolecular interaction and, sufficiently far above the supercooling limit, the decay length is on the order of a molecular dimension. For some materials, we find smecticlike thin films at temperatures above the bulk nematicisotropic transition, enhanced orientational ordering, and the possibility of multiple smecticlike phases.

We describe the results of computer simulations on a model polymer chain with excluded volume interactions in the presence of an external stretching force. For weak and moderate forces the response is linear while for strong forces the behavior is nonlinear, consistent with the non-Gaussian nature of the end-to-end vector $\overrightarrow{R}$ distribution for large $R$. In the vicinity of the $\ominus$ temperature the onset of nonlinearity occurs at larger forces.

Parametric excitation of convective cells by drift waves is considered. Noting that the convective-cell fluctuation of the electrostatic potential is much larger than that of the density, we derive a set of coupled differential equations describing the interaction of the drift waves and the convective cells. For a weak pump, a general dispersion relation which describes three-wave decay and modulational instabilities is given. The growth rate of the latter is found to be generally smaller than that of the decay instability. Our analytical result agrees with computer simulation in which enhanced cells appear in the presence of drift-wave turbulence. The problem of anomalous cross-field diffusion is also discussed.

The time dependences of 35 Cu II energy levels between 15.96 and 24.62 eV were studied using light emission and absorption spectroscopy during the afterglow of a sputtered He-Cu hollow cathode discharge. By measuring the decay of the ${\mathrm{He}}^m\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ and $\mathrm{Cu}\left(4s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\right)$ densities, it was possible to determine the helium species [${\mathrm{He}}^{+}$, ${\mathrm{He}}_2^{+}$, ${\mathrm{He}}^m\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$, and ${\mathrm{He}}_2^m\left(a{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}\right)$] responsible for production of the Cu II states. The Cu II levels between 22.7 and 24.62 eV are produced, either directly or by cascading, by charge exchange between ${\mathrm{He}}^{+}$ and Cu. The Cu II levels between 15.96 and 21.41 eV are produced by charge exchange between ${\mathrm{He}}_2^{+}$ and Cu. No evidence was found for the production of Cu II states by the Penning ionization of Cu by ${\mathrm{He}}^m\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ or ${\mathrm{He}}_2^m\left(a{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}\right)$. A value of 430±10 ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ Torr was measured for the diffusion coefficient of $\mathrm{Cu}\left(4s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\right)$ in helium. The time dependence of the sputtered $\mathrm{Cu}\left(4s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\right)$ radial density profile was also investigated theoretically during the discharge sequence.

A variety of wave patterns bifurcating at a highly degenerate eigenvalue are constructed and sorted out by stability analysis. Depending on the character of nonlinear interaction between excited modes, the stable postcritical state may be a single propagating or standing wave, an ordered pattern of standing waves, or an incoherent pattern comprising a large number of randomly phased modes. In addition, oscillatory destabilization of wave patterns and runaway to large-amplitude solutions are possible. Both ordered and chaotic solutions are generated by one and the same mechanism, and turbulent states which may be numerous and markedly dissimilar, always retain some elements of order.

The spin-exchange cross section $\sigma$ for the collision of hydrogen atoms with ${\mathrm{O}}_2$ and NO have been measured by means of stored atomic-beam spectroscopy. Average values at room temperature are $\sigma (\mathrm{H}-{\mathrm{O}}_2)=(10\mathrm{}\pm 1)\times {10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ and $\sigma (\mathrm{H}-\mathrm{N}\mathrm{O})=(13\mathrm{}\pm 1)\times {10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$. A comparison between our data and pulsed-maser measurements is presented. The development of a passive hydrogen maser based on our bolometric detection technique is proposed.

Elliptically polarized intense electromagnetic waves, under certain conditions, undergo self-precession (frequency $\dot{\rho }$) and shift in wave frequency ($\delta \omega$) due to nonlinear interaction in the magnetized gaseous plasma background. Assuming a classical model of the neutral atom, embedded in the magnetized plasma, the nonlinear distortion of stationary electron orbit is calculated, and the resulting nonlinear polarization is shown to be dependent on intensity-induced nonlinear effects $\dot{\rho }$ and $\delta \omega$ of the strong radiation due to magnetized plasma background. The consequent nonlinear increment in kinetic energy, angular momentum of the bound electron, and consequent induced magnetization $〈M〉$ have been derived. For interaction of ruby laser (power flux ∼ 10 MW/${\mathrm{cm}}^2$, $\lambda =6943\mathrm{}$ Å) in the magnetized ($H_0\sim {10}^2$ gauss) hydrogen plasma ($N\sim \frac{{10}^{12}}{{\mathrm{cm}}^3}$) background, $\dot{\rho }$ and $\delta \omega$ are not very large in nonresonant interactions but are likely to be enhanced in some phase-matching and resonant interactions. The possibility of detection of $〈M〉$ depending on $\dot{\rho }$ and $\delta \omega$ has been discussed. A brief qualitative study is given for the multiphoton excitation of neutral atoms and Zeeman splitting of the spectral lines.

The inverse scattering method is used to investigate the resonant propagation of an optical pulse assumed to be initially unchirped and to have a hyperbolic-secant shape. An exact solution is found for the two-component initial eigenvalue problem. The discrete spectrum consists of a finite set of purely imaginary, equidistant values. The number of discrete eigenvalues (number of solitons) is determined by the initial pulse area $A$. The scattering amplitudes are expressed in terms of Euler gamma functions and hyperbolic functions. In addition to poles in the upper half-plane, the function $\frac{\overline{b}}{a}$ has a pole on the real axis for $A=(2n+1)\mathrm{}\pi$.

The Aharonov-Bohm effect has recently been questioned on theoretical and experimental grounds. Such discussions have suffered from ambiguities which resulted from their focusing on scattering states. It is noted here that the bound-state problem is much simpler. To avoid the Aharonov-Bohm effect in theory requires us to abandon the most fundamental ideas of quantum mechanics. The quantization of flux in superconducting rings and Josephson junctions is a powerful experimental confirmation.

Theoretical estimates for the quadrupole polarizability ${\alpha }_q$ and the dynamical correlation factor $\beta$ are presented for 66 ions in the Li, Na, and Cu isoelectronic sequences. Unlike the dipole polarizability, the theoretical values for these quantities do not agree with analogous empirical parameters deduced from spectroscopic data for the Be, Mg, and Zn isoelectronic sequences using an unpenetrated deformable core model. However, modifications to this model have been suggested which utilize these theoretical values in the prediction of transition wavelengths.