Resonance Auger electron spectra of atomic Rb are studied both experimentally and theoretically. 3$d_{5/2}$ electrons were excited selectively by the monochromated synchrotron radiation to 5p orbitals, and the spectrum of the ejected electrons was measured in the kinetic energy range of 7–95 eV. The experimental spectrum is compared with the calculated theoretical profile. For comparison the normal 3d Auger spectrum was also measured using electron-impact excitation.

Stabilization of the resonantly formed muonic molecular ion (tdμ) depends on the transition from the excited J=1 state to some lower-lying state in competition with decay through the entrance channel. The most important process leading to this transition is internal conversion (Auger effect), in which the excitation energy of the muonic system is carried away by an orbital electron. Using variational wave functions similar to those previously reported [A. K. Bhatia and R. J. Drachman, Phys. Rev. A 30, 2138 (1984)], we have now computed the matrix elements responsible for the transitions. For simplicity, we have assumed that the muonic ion is the nucleus of a hydrogenic atom and have calculated lifetimes and branching ratios for various transitions among the J=0, 1, and 2 states. The J=2 binding energy ($E_2$=101.59 eV) is the first reported variational result for this state. We find that the excited J=0 state is populated several hundred times as often as the ground state.

Absolute values for the generalized oscillator strength (GOS) for the 3$p^6$→3$p^5$(4s,4s’) transitions in argon ${(}^1$${\mathrm{S}}_0$) have been determined by 1-keV electron scattering. The relative differential cross section, measured in the angular range of 1.0°–15°, has been made absolute by comparison with known absolute values for the elastic differential cross section, and the results converted to GOS. The GOS’s have also been calculated, using both the first Born and Glauber approximations, and the results are compared to the experimental values.

The transition rates of atoms inside spherical dielectric particles are computed and studied as functions of the transition frequency and of the physical properties of the host particle. The rates are found to range from about 0.2 to more than 1500 times the free-space value, depending on the location of the atom and other relevant physical parameters. The radiation from distributions of atoms inside liquid drops is also studied. Analytic and numerical results are given for the case of a uniform distribution of excited atoms. Large enhancements of the power output (some 100 times the value for the same distribution in bulk material) are found to occur under resonant conditions.

A detailed theoretical study has been made of the effects of core relaxation and electron-electron correlation on the near-threshold absorption cross section of argon, and the results are compared with previous calculations and experiment. The key results are the following: (1) Within the Hartree-Fock approximation, core relaxation must be included to obtain realistic cross sections; (2) final-state calculations are extremely sensitive to the way in which exchange effects are included in the calculations; (3) although electron-electron correlations produce only small changes in the single-electron cross section, they can account for the two-electron resonances which have been observed immediately above the ionization threshold. In particular, the main resonance above threshold appears to be 1s3$p^5$3$d^2$, which can be reached from the ground state via initial-state correlation.

The d Rydberg series of ${\mathrm{H}}_3$ converging to the lowest rotational level of ortho-${\mathrm{H}}_3^{+}$ has been detected for n values ranging from 27 to 100 using field ionization. The Rydberg molecules are prepared by photoexcitation from the long-lived species, ${\mathrm{H}}_3$ B̃(2${\mathit{p}}^2$${\mathit{A}}_2$’’, N=K=0), in its lowest vibrational level. Extrapolation of the Rydberg series yields an ionization potential of 29562.6±0.5 ${\mathrm{cm}}^{\mathrm{-}1}$. The amplitudes of the excitation spectra reveal the interaction between the ${\mathrm{H}}_3^{+}$ cores with $N^{+}$=1 and 3 via l uncoupling of the d electron, as well as window resonances from interlopers belonging to vibrationally excited ${\mathrm{H}}_3^{+}$ cores.

We study above-threshold ionization (ATI) of a one-dimensional model atom in a time-varying external laser field. The time-dependent Schrödinger equation is integrated in space and time using the Crank-Nicholson method, and the photoelectron energy spectrum is then computed by projecting the wave function onto the energy eigenstates of the time-independent zero-field Hamiltonian. We demonstrate an intensity-dependent ponderomotive shift of the ionization threshold, find a free-electron scaling of the number of ATI peaks with intensity and frequency of the field, and contrast the numerical simulations with two simple Keldysh-type models. For certain field parameters we encounter turn-on transients in the form of ‘‘energy-nonconserving’’ substructure within each ATI peak. Effects on the results of the physical parameters such as length and shape of the laser pulse on one hand, and of the iteration parameters on the other, are discussed in detail.

A photoionization-photodissociation double-resonance technique has been employed to excite transitions from selected rovibrational levels of the metastable c ${}_{}{}^3{}_{}{}^{}\Pi _u^{\mathrm{-}}{}_{}{}^{}$ state to the rapidly predissociated j ${}_{}{}^3{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ state of ${\mathrm{H}}_2$. The photodissociation resonances arise from the configuration interaction between the j ${}_{}{}^3{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ and i ${}_{}{}^3{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ states, and exhibit the asymmetry of Fano-Beutler profiles. These resonances have widths that decrease with increasing v’ from 29 to 10 ${\mathrm{cm}}^{\mathrm{-}1}$; calculated predissociation widths show the same vibrational trend but are consistently 30% smaller. Results have been obtained for the rovibrational energy spacings of high-v levels within each state, and are in good agreement with theory. Photon energies for the c-to-j state transitions are slightly larger than those predicted theoretically.

Time-resolved fluorescence studies of ${\mathrm{Ar}}_2$, ${\mathrm{Kr}}_2$, and ${\mathrm{Xe}}_2$ formed by supersonic jet expansion and excited by monochromatic, tunable, vacuum-ultraviolet radiation have been used to measure the radiative lifetimes of selected, high vibronic levels of the lowest excimer ($A_{1u}$) states. For ${\mathrm{Ar}}_2$, lifetimes of levels v’=24–30 were found to have an average value of 160±10 ns; for ${\mathrm{Kr}}_2$, levels v’=32–38 had average lifetimes of 56±5 ns; and for ${\mathrm{Xe}}_2$, levels v’=36–43 had average lifetimes of 45±6 ns. These lifetimes for ${\mathrm{Ar}}_2$, ${\mathrm{Kr}}_2$, and ${\mathrm{Xe}}_2$ differ by factors of approximately 20, 5, and 2, respectively, from values for the v’∼0 levels obtained earlier with high gas pressures and excitation by charged particles or synchrotron radiation. It is shown that these large variations in radiative lifetimes with vibrational level arise from increases in electronic transition moments as internuclear distances increase from equilibrium values to those corresponding to the high vibrational levels. The agreement between all measured lifetimes and calculated values (with spin-orbit coupling included) is well within the accuracy permitted by the presently known spectroscopic constants of ${\mathrm{Ar}}_2$, ${\mathrm{Kr}}_2$, and ${\mathrm{Xe}}_2$.

The supra-K${\alpha }_1$ satellite spectrum of Cu was measured using a high-resolution monolithic-double-crystal spectrometer. Its total intensity relative to that of the K${\alpha }_1$ line was found to be 6×${10}^{\mathrm{-}3}$, in good agreement with the only published measurement and the theoretical predictions. The spectrum includes fine structure. Relativistic Dirac-Fock (RDF) and nonrelativistic Hartree-Fock calculations were carried out and compared with the measured data in detail. The RDF calculations allow assignment of all seven structural features detected in the measured spectrum to 2p-spectator-hole transitions, with a possible small contribution from 2s-spectator-hole transitions. The new line assignments are discussed and compared to earlier work. Similar measurements were also done in the energy range between the K${\alpha }_1$ and K${\alpha }_2$ lines. Only one possible feature, on the limit of statistical significance, was found close to the energy predicted for a radiative Auger transition involving a 3d electron. Its relative intensity, 5×${10}^{\mathrm{-}4}$, is much lower than predicted theoretically but within a factor of 2 from recent measurements of equivalent electron-capture-excited transitions.

Using the Green’s-function method, the $M_5$-$N_{23}$$N_{45}$ Auger energy of the atomic Xe (Z=54) is calculated. In contrast to the Dirac-Hartree-Fock self-consistent-field (ΔSCF) method, which gives very poor agreement with the experiment both in absolute Auger energies and multiplet splitting energies, the present theory gives a good agreement with the experiment. The importance of the configuration interaction between the final double-hole level with the triple-hole one-electron continuum is pointed out as a cause of the large discrepancies between the ΔSCF results and experiment.

The L${\gamma }_2$,3(2${\mathrm{s}}^{\mathrm{-}1}$→4${\mathrm{p}}^{\mathrm{-}1}$) x-ray emission spectrum of gaseous xenon was measured in fluorescence with a high-resolution vacuum double-crystal spectrometer. The spectrum was also calculated by the Green’s-function method. The agreement is excellent. It is shown that the spectrum can be interpreted essentially in terms of the spectral function of the 4p hole. The effects of the initial 2s-hole state on the final 4p-hole state are small. The spectrum shows that the quasiparticle picture of a 4p hole in xenon breaks down because of strong 4$p^{\mathrm{-}1}$⇆4$d^{\mathrm{-}2}$4(n,ɛ)f super-Coster-Kronig processes.

This paper is devoted to the autoionization process of large-angular-momentum Rydberg states. After a brief account of autoionization formalism in nonrelativistic theory and single-configuration approximation, we apply it to atomic states with one electron of large angular momentum. The dominant contribution is the direct one and the exchange contribution is ignored. In this framework, the autoionization width varies with the principal quantum number as $n^{\mathrm{-}3}$ and exponentially with the angular momentum. When two excited electrons interact with a spherically symmetric core, it is demonstrated that the interaction between the Rydberg electron and the core polarized by the valence electron is proportional to the interaction between the two active electrons. Using newly derived radial matrix elements, we obtain a generally good agreement between our results and experiments on barium and strontium. Large-l Rydberg states are shown to be stable versus autoionization as soon as l is about 7. Possible refinements of our method are reviewed.

The multiphoton ionization spectra of several arene molybdenum tricarbonyls have been measured in the region 350–420 nm. These spectra exhibit allowed, two-photon resonant ns ${}_{}{}^7{}_{}{}^{}$${\mathit{S}}_3$ and nd ${}_{}{}^7{}_{}{}^{}$${\mathit{D}}_{\mathit{J}}$ Rydberg series of neutral bare molybdenum atoms. Furthermore, the electric field inherent to the multiphoton ionization experiment also permits observation of the nominally forbidden np ${}_{}{}^7{}_{}{}^{}$P${\mathrm{°}}_{\mathit{J}}$ Rydberg series. A nonlinear least-squares regression of the Rydberg equation was used to obtain an improved ionization potential of molybdenum and the quantum defects of the three series.

A novel effect, the magnetic analog of the transverse Pockels effect (MATPE), is calculated theoretically in a phenomenological approach for transparent crystals. The linearly polarized probe beam on traversal of the crystal under the action of a magnetic field ${\mathrm{B}}^0$ exhibits elliptical polarization, proportional to the first power of ${\mathrm{B}}^0$ and also to the axial third-rank tensor ${}_{\mathrm{e}}{}^{\mathrm{}\left(1\right)\mathrm{}}{}_{}{}^{}\mathrm{\alpha }_{\mathrm{e}\left(\mathrm{ij}\right)\mathrm{k}}^{\mathrm{}\left(1\right)\mathrm{}}{}_{}{}^{}$(ω) of linear magnetic variations in the electric permeability antisymmetric with respect to time inversion and symmetric in its first two indices. Applying group-theoretical methods involving time-inversion arguments, we show that the effect occurs only in magnetic-symmetry classes and is most easily observable in the Voigt setup ${(\mathrm{B}}^0$ at right angles to the propagation direction of the probe beam) in transparent centrosymmetric antiferromagnetic crystals. The most suitable setup for experimental observations of MATPE is that with the linearly polarized beam propagating along the optical axis of antiferromagnetic crystals with the symmetries 3¯m, 6/m, and 6/mmm.

We have investigated the interaction of a single atom with a single mode of the radiation field in an ideal cavity when the field is initially in a squeezed-vacuum state. In particular, we present results for the spectrum of the emitted light and for the time evolution of the squeezing inside the cavity. Our results contrast sharply with previous studies of single two-level atom interaction with a continuum of squeezed-vacuum modes. In particular, the results are shown to be insensitive to the initial phase of the atomic dipole relative to the squeezed field, and the squeezing is destroyed by the coherent interaction, in a time essentially independent of the initial degree of squeezing. Most features of the spectrum are very similar to those predicted for an initial thermal state, although the two-peaked structure associated with vacuum-field Rabi splitting is more apparent for a squeezed state with a small average number of photons than for a thermal state with the same number of photons.

We present a quantum theory of light pressure in external classical fields, consistently incorporating both the electric and the magnetic components of the radiation. We start with the equation of motion of the gauge-independent Wigner function governing the individual charged constituents of the atom, separate the center of mass and internal degrees of freedom in the presence of the external field with the aid of an expansion that goes one order beyond the dipole approximation, and finally specialize to a near-resonantly driven two-state atom. The ensuing light-pressure theory turns out to be equivalent to the standard approach, even though in our treatment it is imperative to retain the magnetic field which does not appear explicitly in the conventional theory.

We have calculated the spin-exchange shifts of the ground-state Δ$m_F$=0 transition of a gas of hydrogen atoms in zero magnetic field from zero temperature up to temperatures of 1000 K. Taking into account the hyperfine interaction during spin-exchange collisions we find shifts nonlinear in the atomic linewidth and not compensated for by the usual methods of tuning the microwave cavities of oscillating hydrogen-maser frequency standards. At room temperatures these shifts affect the H-maser stability at the level of δω/ω≃${10}^{\mathrm{-}15}$. At cryogenic temperatures these shifts are large compared to the potential thermal instabilities of liquid-helium-lined hydrogen masers. A detailed study of these nonlinear shifts reveals several ways to reduce these new sources of frequency instability.

For the Hamiltonian of a single mode of an electromagnetic field that preserves coherent states, the general form of the time-dependent Hermitian invariant, of which a given stable coherent state is an eigenstate, is obtained with an appropriate initial condition. The result may be generalized to give a similar invariant for a Hamiltonian that preserves any particular class of unitarily transformed coherent states such as squeezed states.

We consider how the finite transmission of the output mirror of a laser operating well above threshold affects laser phase diffusion in the quantum regime. In our traveling-wave analysis, the cavity loses field energy discretely only once every round trip. For a low-Q cavity, the linewidth that arises from phase diffusion can differ significantly from the Schawlow-Townes result derived using traditional theories based on a distributed-loss picture.