The relative photoionization cross sections of Kr 3d, 4s, and 4p levels have been determined from photoelectron measurements using synchrotron radiation in the photon energy range 37–160 eV. By using the total absorption cross sections from absorption measurements (Marr and West) the absolute partial cross sections have also been determined. The experimental results are compared with the theoretical calculations of Huang et al.

When ions of slightly different mass and the same charge are stored in a radio-frequency electric quadrupole trap, a collective oscillation is observed rather than the independent motions usually assumed. A high-temperature model of ion clouds, each characterized by ions of one mass, shows that the ions of each cloud move as a unit and exhibit a correlated motion with the other clouds when a strong coupling condition is satisfied. This phenomenon is expected to arise whenever more than one ion is trapped and might be observable in neutral atom traps as well.

The microwave-cavity mode pattern has been directly observed in an old-style compensated Penning trap by a simple bolometric technique which monitors changes in the temperature of the axial center-of-mass motion for a cloud of electrons. The method allows one to easily determine the position of individual modes to a precision better than 0.01%. Presently, over 60 modes have been observed for fields between 17 and 60 kG and an upper limit estimate of 2300 has been made for the cavity Q.

External bremsstrahlung spectra produced by the complete absorption of β particles from the decay of ${}_{}{}^{90}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Y}$, and ${}_{}{}^{204}{}_{}{}^{}\mathrm{Tl}$ in thick targets of Cu, Cd, Ta, and Pb are measured using a NaI(Tl) detector. The photon and energy yields and energy-yield constant are calculated using the unfolded bremsstrahlung spectra. The experimental data are compared with the numerical calculations based on the formulation of Pratt and his collaborators and the Born approximation theory of Bethe and Heitler. The experimental data agree with the Elwert-corrected Bethe-Heitler theory within experimental uncertainties for Cu and Cd, and a systematic positive deviation is found for Ta and Pb. The experimental data show good agreement with the numerical screened calculations of Pratt and his collaborators. The energy-yield constant is found to exhibit an energy dependence.

The rotational hyperpolarizability of a homonuclear diatomic molecule is calculated for all off-resonance third-order nonlinear optical processes. The treatment of rotations is fully quantum mechanical. The classical limit of the expression obtained for the dc Kerr effect agrees with the classical calculation in the static limit, but differs by a factor of (3/4 at optical frequencies.

It is shown that if one has access to only one mode of a two-mode squeezed-vacuum state, the photon statistics of this mode is indistinguishable from that of a thermal distribution. Parametric interactions that give rise to two-mode squeezing thus provide a mechanism for thermalization that is intrinsically quantum mechanical.

We have studied two simple model tunneling problems involving an electron in two spatial dimensions in the presence of a high magnetic field, both by numerical integration of Schrödinger’s equation, and by a semiclassical evaluation of the coherent-state path integral. We find that the semiclassical approach is analytically tractable and produces results in good agreement with the numerical results.

We have adopted the Lagrange-multiplier method, previously used to determine Lyapunov spectra, to the ‘‘subtraction technique’’ introduced by Ciccotti, Jacucci, and McDonald [J. Stat. Phys. 21, 1 (1979)]. By adopting this approach we had hoped to minimize the influence of statistical fluctuations at long times on the linear response to external fields. We used Lagrange multipliers to constrain the phase-space separation dr=(dq,dp) between two trajectories: an unperturbed equilibrium trajectory and a perturbed nonequilibrium trajectory. Although the Lagrange-multiplier constraint does eliminate much of the statistical noise, the correlations themselves are modified in an unacceptable way, artificially increasing the apparent diffusion coefficient while reducing the apparent heat conductivity.

Qualitative differences have been observed between two types of "quasi-one-electron" collision systems. We have studied valence-electron excitation at "high" energy (relative collision velocities up to 0.5 a.u.) in the ${\mathrm{Mg}}^{+}$+He and ${\mathrm{Na}}^{+}$+H collision systems, and find that while ${\mathrm{Mg}}^{+}$+He collisions are dominated by "direct" excitation, the ${\mathrm{Na}}^{+}$+H collisions exhibit significant "molecular" excitation, even at the highest velocities. This behavior can be understood in terms of the molecular structure of the respective collision complexes, and the energy separation between the ground and first excited states of the valence electron.

Berry, Simon, and Aharonov and Anandan have discovered, interpreted, and generalized a geometrical phase factor that occurs for a quantum state evolving around a closed path in the projective Hilbert space of rays. Here this phase is directly given in terms of the holonomies of several natural geometrical structures on the projective space.

We propose a new scheme for obtaining soft x-ray gains in neonlike ions. The scheme relies on inner-shell ionization of sodiumlike ions by suprathermal electrons. Since this amplifier will operate with, in principle, no population in the neonlike ground state, the power requirements for scaling to higher $Z$ may be reduced, and the problem of line trapping is eliminated. Model calculations for selenium are presented to verify measurable gain and the experimental feasibility of the scheme is briefly discussed.

We have precisely measured the vacuum ultraviolet intervals between several rotationally and vibrationally excited levels of ground-state ${\mathrm{H}}_2$ and the $E$, $F{{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}}^{+}$ state. An accuracy of 0.01 ${\mathrm{cm}}^{-1\mathrm{}}$, an order of magnitude better than previously available, is achieved using a pulsed discharge source in conjunction with a pulse amplified cw laser system. These measurements also serve as a calibration for numerous other excited states connected by optical intervals to the $E$, $F$ state.

An interference between electric quadrupole and Stark-induced dipole amplitudes is observed for the first time in calcium. From our measurement of the atomic polarization produced by this interference we obtain $A(4s4p{}_{}{}^1{}_{}{}^{}P-4s3d{}_{}{}^1{}_{}{}^{}D)=(3.68\mathrm{}\pm 0.89\pm 0.11)\times {10}^3$ ${\mathrm{s}}^{-1\mathrm{}}$. This result suggests that the laser cooling of atomic calcium is feasible.

Separated-oscillatory-field interference signals from the 14-GHz $2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-2\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ Lamb-shift transition in ${\mathrm{He}}^{+}$ have been observed using a new phase-variation technique. Instead of scanning the frequency over a broad range, the interference signal is measured as a function of the relative phase of the microwave field in the two interaction regions. The resonance frequency is determined from the frequency dependence of the phase at which the signal is a maximum.

Absolute bound-bound atomic two-photon cross sections have been measured using a single-frequency laser for the first time, eliminating the usual uncertainties about unresolved temporal fluctuations. For the $3p{}_{}{}^3{}_{}{}^{}P_{J^{\prime }}^{}{}_{}{}^{}\leftarrow 2p{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ transition in atomic oxygen at 226 nm the integrated cross section is $\Sigma {J^{\prime }}^{}{\sigma }_0^{\mathrm{}\left(2\right)\mathrm{}}(J^{\prime }\to 2)=1.87\mathrm{}\pm 0.60\times {10}^{-35\mathrm{}}$ ${\mathrm{cm}}^4$. Doppler-free spectra have been used to measure relative fine-structure cross sections and energy spacings. Absolute and relative two-photon cross sections agree well with perturbation theory, validating this approach.

We present theoretical and numerical results showing that the probability distribution on energy levels of highly excited hydrogen atoms produced by a monochromatic field should be exponentially localized in the number of absorbed photons. These results allow for a new interpretation of underthreshold ionization and also for an estimate of the ionization rate.

For a binary-fluid layer heated from below, we evaluate the effects of the temperature and concentration dependence of the thermodiffusion ratio $k_T$ as well as the influence of barodiffusion on the conductive state and its stability.

In this paper the so-called Feynman-Vernon influence functional theory has been generalized in order to include the possibility of dealing with initial conditions of the system plus environment other than the factorizable one. It has been shown that the new influence functional can now be written in terms of paths which represent the coupling of quantum-statistical to quantum-dynamical effects. Once the thermal paths are integrated out of this new influence functional, a generalization of the original Feynman-Vernon expression is obtained.