Radiative lifetimes for seven levels of the z ${}_{}{}^4{}_{}{}^{}\mathrm{°}$, ${}_{}{}^4{}_{}{}^{}$D°, and ${}_{}{}^4{}_{}{}^{}$F° terms of Fe ii have been measured by using laser excitation of a beam of fast ${\mathrm{Fe}}^{+}$ ions. The ratio of the measured lifetime to that calculated from Kurucz’s gf values appears to increase systematically with the energy of the levels involved.

Using the recently developed relativistic Wigner formulation for the density matrix of spin-1/2 particles, we study the ${}_{}{}^{\mathrm{\pi }}{}_{}{}^{}$=1/$2^{+}$ Coulomb-like and cavity relativistic states. One of our objectives is to understand the sharing of the total angular momentum of a quantum state between the spin and rotational degrees of freedom, arising due to the spin-orbit coupling. Another is to demonstrate that the 4×4-matrix Wigner function is the appropriate generalization from the 2×2 form of the nonrelativistic theory.

A method of calculating the one-loop self-energy contribution to the Lamb shift is presented. The technique relies on the division into the low- and the high-energy parts. The low-energy part is calculated using the multipole expansion and the high-energy part is calculated by expanding the Dirac Coulomb propagator in powers of the Coulomb field. This method is a generalization of the original Bethe derivation of the leading-order contribution.

Recent experimental studies of the spin dependence in electron-impact ionization of atomic hydrogen revealed the presence of deviations from the predictions of the conventional Wannier threshold theory of two-electron escape. We provide some insight into the possible origin of these deviations and reexamine the results of previous work that had claimed consistency with the Wannier theory but, with added statistical analysis, also seem to show deviations.

The effect of the Coulomb repulsion between the two ejected electrons on the angle-resolved cross section is examined; it is shown that in the general case the effective-charge approximation is not in agreement with solutions of the three-body Schrödinger equation with the appropriate asymptotic boundary conditions, and an approach is proposed in order to introduce the electron repulsion in the calculation of the sixfold differential cross section ${\mathit{d}}^6$${\mathrm{\sigma }}^{2+}$/${\mathit{d}}^3$k${\mathit{d}}^3$k’.

We have recalculated the dielectronic recombination rate coefficient for the special case of ${\mathrm{O}}^{+}$ using an improved atomic structure. This removes the discrepancy between the results of Terao et al. [J. Phys. B 24, L321 (1991)] and of Badnell and Pindzola [Phys. Rev. A 39, 1690 (1989)].

The effects of relaxation on the photodetachment of the iodine negative ion are calculated using the recently developed relativistic random-phase approximation with relaxation. In this method the outgoing electron is calculated in the field of the relaxed negative ion with one electron removed (i.e., in the field of the atom). Overlap integrals between orbitals of the initial and final states are included. It is found that the relaxation effects for the negative iodine atom are significantly larger than those for the corresponding neutral atom Xe. Comparison is made with results calculated by the relativistic random-phase approximation and with experiment near the 5p threshold.

The existence of the classical Thomas peak in the angular distribution of projectiles undergoing capture in collisions of 5-MeV protons with atomic hydrogen is explored using the three-body, three-dimensional classical-trajectory Monte Carlo technique. A method that selects only that portion of the initial phase space which yields capture at this energy was developed to make the calculation tractable due to the extremely small cross section. The spectrum obtained displays only a small shoulder near the angle predicted by Thomas on the basis of successive classical binary collisions and the total (integral) cross section is overestimated by a factor of 26 compared to recent experimental measurements. The overestimation originates from too large a contribution from velocity matching direct capture; the energy regime in which it is significant is discussed. In addition, the double-scattering events in this model which contribute significantly to the cross sections are found to differ substantially from the Thomas picture.

Distinctive optical emission bands have been observed during the etching of gold films in ${\mathrm{O}}_2$-${\mathrm{CF}}_4$ and ${\mathrm{O}}_2$-${\mathrm{SF}}_6$ rf glow-discharge plasmas. We suggest that the emission originates from gas-phase AuF, although AuO and the molecular ions ${\mathrm{AuF}}^{+}$ and ${\mathrm{AuO}}^{+}$ cannot be definitively ruled out as the emitting species. No optical spectra have previously been reported for any of these species in the gas phase. Conditions for producing the emission bands are outlined, and a representative spectrum is provided. Band positions for the tentatively identified (v′=v″,v″) and (v′=v″-1,v″) progressions could be reproduced with a (0,0) band origin ${\nu }_{00}$=17 757 ${\mathrm{cm}}^{\mathrm{-}1}$, vibration frequencies ${\mathrm{\omega }}_{\mathrm{e}}^{\prime }$=529.5 ${\mathrm{cm}}^{\mathrm{-}1}$ and ${\mathrm{\omega }}_{\mathrm{e}}^{\mathrm{″}}$=560 ${\mathrm{cm}}^{\mathrm{-}1}$, and vibrational anharmonicities ${\mathrm{\omega }}_{\mathrm{e}}^{\prime }$${\mathrm{x}}_{\mathrm{e}}^{\prime }$=2.5 ${\mathrm{cm}}^{\mathrm{-}1}$ and ${\mathrm{\omega }}_{\mathrm{e}}^{\mathrm{″}}$${\mathrm{x}}_{\mathrm{e}}^{\mathrm{″}}$=1.0 ${\mathrm{cm}}^{\mathrm{-}1}$, where the vibrational energies relative to the v=0 levels are given by ${\mathrm{G}}_0$(v)=(${\mathrm{\omega }}_{\mathrm{e}}$-${\mathrm{\omega }}_{\mathrm{e}}$${\mathrm{x}}_{\mathrm{e}}$)v-(${\mathrm{\omega }}_{\mathrm{e}}$${\mathrm{x}}_{\mathrm{e}}$)${\mathrm{v}}^2$. The band structure could be qualitatively accounted for by a ${\mathrm{\Pi }}^1$–${\mathrm{\Sigma }}^1$ band system with an assumed ${\mathrm{B}}_{\mathrm{e}}^{\mathrm{″}}$ of 0.24 ${\mathrm{cm}}^{\mathrm{-}1}$, ${\mathrm{B}}_{\mathrm{e}}^{\prime }$=${\mathrm{B}}_{\mathrm{e}}^{\mathrm{″}}$+2.75×${10}^{\mathrm{-}3}$ ${\mathrm{cm}}^{\mathrm{-}1}$, ${\mathrm{\alpha }}_{\mathrm{e}}^{\prime }$=4.5×${10}^{\mathrm{-}3}$ ${\mathrm{cm}}^{\mathrm{-}1}$, and ${\mathrm{\alpha }}_{\mathrm{e}}^{\mathrm{″}}$=1.0×${10}^{\mathrm{-}3}$ ${\mathrm{cm}}^{\mathrm{-}1}$, where the rotation constants are given by ${\mathrm{B}}_{\mathrm{v}}$=${\mathrm{B}}_{\mathrm{e}}$-${\mathrm{\alpha }}_{\mathrm{e}}$(v+12).

A useful criterion for atomic ionization in classical mechanics is the ‘‘compensated energy,’’ which temporally evolves from the negative initial binding energy to a stationary positive value as the electron is ejected. Herein we give the quantum-mechanical analog of this quantity.

We report the experimental observation of an intermittent route to chaos of a single-mode ring laser. We show that by analyzing the experimental data in a time-inverted manner, the observed intermittency can be well described by type-I intermittent dynamics.

Atomic resonance fluorescence, emitted near the surface of a four-wave-mixing phase conjugator, exhibits squeezing for certain values of the optical parameters of the incident laser field and for a certain range of the phase-conjugate reflectivity. A condition for the occurrence of squeezing is derived, and it is shown that the presence of the phase-conjugating medium tends to increase the quantum fluctuations, thereby diminishing the squeezing.

The phenomenon of photon antibunching in the micromaser is investigated. It is shown that for a wide range of the pump parameter the micromaser photons exhibit antibunching, although they need not obey sub-Poissonian statistics.

We show that the amplitude Nth-power squeezing can be produced in kth-harmonic generation. The amplitude Nth-power squeezing of the fundamental can exist if the kth harmonic is originally in a coherent state which includes the vacuum. It is also shown that the normal squeezing of the kth harmonic depends on the amplitude kth-power squeezing of the fundamental.

In view of a renewed interest in the theory of multiply excited resonances [M. Bylicki, Phys. Rev. A 39, 3316 (1989); 40, 1748 (1989); 41, 4093 (1990)] and the related comment by Chung [Phys. Rev. A 41, 4090 (1990)], I present a brief analysis of aspects of the theory for the identification and computation of resonances in many-electron systems. As examples, I use the ${\mathrm{He}}^{\mathrm{-}}$ 2s2${\mathit{p}}^2$ ${}_{}{}^4{}_{}{}^{}$P and ${}_{}{}^2{}_{}{}^{}$D triply excited resonances.

In the preceding Comment [C. A. Nicolaides, Phys. Rev. A 46, 690 (1992)], a few statements have been made in regard to the saddle-point method developed by Chung [Phys. Rev. A 20, 1743 (1979)]. In this Reply, statements made in the preceding Comment are further discussed to clarify any possible misconceptions.

Motivated by the existence of a fractal phase boundary for the occurrence of Kolmogorov-Arnold-Moser tori in two-parameter area-preserving maps, we study the two-parameter circle map with two inflection points. The critical surface of the mode-locked windows is found to obey additive rules for the bistability regimes caused by cusp catastrophe. This results in the double devil’s staircase for the mode-locked windows and a fractal curve for a critical set of parameter values for the breakup of the invariant circles.

We study the classical motion of a relativistic two-body system, in 1+1 dimensions, with interaction described by a relativistic generalization of the well-known Duffing potential. The equations of motion are separable in hyperbolic coordinates and are solved in quadrature. The radial equation (in the invariant variable corresponding to the spacelike distance between the particles) has an effective potential depending on the separation constant for the hyperbolic ‘‘angular momentum,’’ and analytic solutions are obtained for the separatrix motion. In the presence of weak driving and damping forces, the Melnikov criterion for the existence of homoclinic instability is applied, and it is shown that chaotic behavior is predicted for sufficiently strong driving forces (bounds are given).

Using deformed bosons, we construct generalized anharmonic oscillators suitable for the description of vibrational spectra of diatomic molecules. One of them gives the same spectrum as the modified Pöschl-Teller potential, i.e., the first two terms of the Dunham expansion, while the other is a q deformation of the first, corresponding to summing all terms of the Dunham expansion for vibrational molecular spectra.