A comparative study of three recent theoretical formalisms by Anholt, Scofield, Becker, and co-workers for K-shell ionization by highly relativistic protons has been carried out. The importance of the spin-flip mechanism is emphasized. It is concluded that in the analysis of such inner-shell ionization processes, an accurate description of the projectile-target interaction is of much more significance than the accuracy of the wave functions of the atomic electrons.

The approach to equilibrium found recently by Georgallas [Phys. Rev. A 35, 3492 (1987)] is analyzed and compared with previous work on this problem.

Using the well-known solution for a two-level atom interacting with a single mode of radiation (Jaynes-Cummings model), we reanalyze the possibility of squeezing. We found that if only the initial coherent state has a mean photon number exceeding 10 (for a resonant case) significant squeezing can be achieved. Its strength can be arbitrarily large for increasing average photon number. Finally, we solve our model in the situation when the em field is damped and analyze the impact of damping on both squeezing and revival phenomena.

Experimental results establishing for the first time the electroclinic effect in smectic-B and -E phases of chiral molecules are reported, which were obtained on a compound showing the phase sequence isotropic-SmA-SmB-SmE. The induced tilt angle is found to be proportional to the applied field strength in all the three smectic phases indicating a linear tilt-polarization coupling. The ratio between induced polarization and induced tilt angle, determined by simultaneous measurement of both quantities, is nearly temperature independent within a phase and increases at the transitions SmA to SmB and SmB to SmE.

The amplitude of the parity-nonconserving (PNC) electric-dipole transition 6s→7s in cesium is calculated to third order in many-body perturbation theory. Inclusion of the corresponding corrections in calculations of parity-conserving transition amplitudes and atomic hyperfine constants leads to agreement with experiment at a level under 5%. We obtain a value of 0.951${\mathrm{iea}}_0$×${10}^{\mathrm{-}11}$$Q_W$/-N with an estimated error of 5% for the PNC amplitude. A determination of the Weinberg angle is made by combining the present calculation with recent measurements of the PNC amplitude: the result is ${\sin }^2$${\mathrm{\theta }}_{\mathrm{W}}$=0.229 ${\mathrm{}\left(24\right)\mathrm{}}_{\mathrm{expt}}$ ${\mathrm{}\left(16\right)\mathrm{}}_{\mathrm{theor}}$. Issues involved in improving the accuracy of the calculations of atomic properties of cesium are discussed.

Using a simple liquid-droplet model, we give a comprehensive description of the process by which doubly charged molecular clusters disintegrate into singly charged fragments. The minimum calculated sizes of stable clusters are in good agreement with experiment. The failure to observe the fragments of doubly charged clusters is also explained, while we claim that triply charged ${\mathrm{CO}}_2$ clusters fragment by a different thermal process.

Klauder’s continuous representation naturally allows a basic length scale. It is assumed to be fundamental for continuous dynamical variables Q and P in a general quantum theory. We explore new properties of a particle’s coordinates at short distances by constructing continuous base states in the coordinate space rather than in the phase space. The results show that the position operator Q has neither eigenvalues nor eigenvectors. There emerges a picture of ‘‘fuzzy point particles’’—point particles whose positions can never be measured with an accuracy smaller than Δ$q_{\min =\mathrm{R}}$, where R is a very small length scale for the coordinate variable. In the limit R→0, Klauder’s continuous representation reduces to Dirac’s eigenbras and kets. The property Δq≥R implies that waves with arbitrarily short wavelengths do not exist in the physical world.

The zero-momentum energy expression has been proposed as a sensitive criterion for assessing the accuracy of approximate wave functions. The original expression is shown to lead to an indeterminate 0/0 form for all states other than spatially symmetric one-electron doublets and two-electron singlets. This paper presents a modified version which extends its applicability to arbitrary N-electron states with no restriction on spatial symmetry or spin multiplicity. Since it is a linear functional of the wave function, it is more sensitive to wave-function error than is the usual expression for variational energy.

A new recently proposed dispersion relation (DR) [Temkin, Bhatia, and Kim, J. Phys. B 19, L707 (1986)] is tested for e-He scattering; the results show that the new DR is not satisfied. Therefore we start to investigate the analytic structure of the difference amplitude, previously assumed to be nonsingular, on the negative scattering energy axis. Even under severe approximations we find that the difference amplitude contains both poles and branch points. This suggests, however, a useful approximation of these contributions to the DR which gives very satisfactory agreement in both e-H and e-He scattering. We conclude with some brief general remarks on this problem.

The algebraic-eikonal approach to electron-molecule scattering is extended to triatomic molecules. In addition to the dipole interaction we include the polarization potential, adopting a distorted-wave eikonal approximation in which the dipole interaction is still treated in the eikonal approximation. We derive a simple expression for the dipole transition matrix elements which is numerically very effective. Finally, our method is applied to calculate the differential cross section for scattering electrons from HCN.

Pressures shifts and broadenings of 5snd ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ Rydberg levels of Sr i due to noble gases have been measured by means of Doppler-free two-photon excitation and thermionic detection for a wide range of principal quantum numbers (11<n<150). High accuracy was achieved by means of an active optical-frequency standard. Our results agree well with experimental data obtained by other groups for related systems and confirm existing theories for line shifts and broadenings. Scattering lengths for the various gases extracted from the spectroscopic results for high n show satisfactory agreement with corresponding data from low-energy electron-scattering experiments. With the exception of argon, the same is true for dipole polarizabilities when compared with known values. For neon we find evidence for nonlinear shifts at high principal quantum numbers (n≥100).

Positron creation in crossed-beam collisions of high-energy, fully stripped heavy ions is investigated within the coupled-channel formalism. In comparison with fixed-target collisions of highly stripped heavy-ion projectiles positron production probabilities are enhanced by more than one order of magnitude. The increase results from the possibility to excite electrons from the negative energy continuum into all bound states. The positron spectrum is shifted towards higher energies because of the absence of electron screening. Rutherford scattering as well as nuclear collisions with time delay are investigated. We also discuss the filling of empty bound states by electrons from pair-production processes.

We study the problem of laser-assisted electron–hydrogen-atom elastic scattering in the general case when the electromagnetic field is elliptically polarized, and obtain the results for plane-polarized and circularly polarized electromagnetic fields as special cases. We extend the work of F. W. Byron and C. J. Joachain [J. Phys. B 17, L295 (1984)] by considering all higher-order terms of the laser-modified atomic wave function, which have increasingly important effects on the scattering amplitude for small momentum transfer when the number of photons emitted or absorbed increases. We set up recurrence relations for determining all higher-order coefficients in the spectral expansion of the laser-dressed wave function and also determine all higher-order terms in the energy shift and the time-dependent phase. Our general expression for the laser-assisted first-Born-approximation scattering amplitude for l-photon transfer is cast into a form which gives the probability for the case in which $l^a$ photons are absorbed or emitted by the bound atomic electron and the remaining (l-$l^a$) photons by the free projectile electron. We discuss the dependence of the scattering amplitude on the polarization of the electromagnetic field. Exchange effects in the presence of the laser are also taken into account in a simple though approximate manner. We further discuss the problem of replacing the above-mentioned first-Born-approximation scattering amplitude by some higher-order scattering amplitude in the presence of the time-dependent laser field.

We calculate the cross sections associated with the electronic capture and loss of B, C, N, and O ions moving in a solid target with velocities v∼${\mathrm{Zv}}_0$ (where $v_0$ is the Bohr velocity). Three mechanisms are considered: Auger processes, whereby an electron is captured or lost creating an electronic excitation in the solid; resonant processes, coherently induced by the target crystal potential; and direct capture of electrons from the target inner shells. Atomiclike processes control the charge transfer for the velocities v≳${\mathrm{Zv}}_0$. The distribution of charge states has been calculated as a function of the ion velocity. Good agreement is found with the available experimental data.

An electron-photon coincidence technique has been used to measure an angular-correlation function for the excitation of the 3 ${}_{}{}^2{}_{}{}^{}P$ state in sodium at an incident electron energy of 54.4 eV; the scattered electrons are detected at 5°. It is shown that the depolarizing influence of the hyperfine structure in the excited state is such that the angular correlation is essentially isotropic. Thus severe limitations are imposed on the use of this technique for the study of scattering amplitudes in the electron-impact excitation of sodium atoms.

In the present research we have used a Fourier spectral analysis to study line profiles due to strong atom-atom interactions in the limit of high perturber density. The presence of multiple satellites in this case is well explained. Moreover, for decreasing interactions and densities we may extrapolate our results and explain the disappearance of the satellites. The use of ‘‘a crude potential shape’’—here a square-well—proves to be sufficient to explain the presence of multiple satellites and determine the necessary physical conditions for their appearance.

We introduce a new simulation technique which is based on the distribution of the times of collision between plasma particles and a radiating atom. This procedure generates a continuous flow of particles of random velocities and directions through a sphere of interaction around the radiator. It leads to correct statistics while traditional procedures with their reinjection prescriptions are shown to change the statistics. The new technique is applied to a detailed study of Ly-α. The influence of the shielding parameter and the temperature-density dependence are investigated. An asymptotic exponential falloff of the ion dipole autocorrelation function is exhibited, verifying analytic indications. The first joint ion-electron simulation of profiles is reported. They agree with the experimental profiles of Grützmacher and Wende.

The core-excited quartet spectrum of Na i produced by beam-foil excitation has been studied in the 3300–5500-Å region. Sixteen new lines, representing transitions between the 2$p^5$3s3p, 2$p^5$3s3d, and 2$p^5$3s4s configurations, are reported, together with the lifetimes for 12 of the levels belonging to the 2$p^5$3s3d and 2$p^5$3s4s configurations. Some of the lifetimes deviate considerably from recently published values [L. Engström, L. Young, L. P. Sommerville, and H. Berry, Phys. Rev. A 32, 1468 (1985)], including the lifetimes of the 2$p^5$3s3d ${}_{}{}^4{}_{}{}^{}\mathrm{D}_{3/2}^{}{}_{}{}^{}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{F}_{5/2}^{}{}_{}{}^{}$ levels, which have both been suggested for use in an extreme ultraviolet (xuv) laser. The experimental data for fine-structure splittings and lifetimes are in good agreement with multiconfiguration Hartree-Fock calculations.

Weak branching out of the 6${\mathrm{s}}^2$ ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$⇆6s6p ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ two-level system to the metastable 6s5d ${}_{}{}^1{}_{}{}^{}$,3D states has been measured for ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ using cw-resonance ionization mass spectrometry on an optically pumped atomic beam. A branching ratio (inverse branching fraction) of 440±40 was obtained.

X-ray and Auger transition rates from doubly excited 2${p^2}^1$${\mathrm{D}}_2$, 2${s^2}^1$${\mathrm{S}}_0$, 2p3p ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$, 2$p^2$ ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$, and 2p4d ${}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ states of heliumlike ions are presented for Z=10, 14, 18, 20, 22, 24, 26, and 28. Intensity factors of x-ray satellites originating from dielectronic recombination of ground-state hydrogenic ions via the above autoionizing states are also calculated. The calculations are performed in the intermediate-coupling scheme with the inclusion of configuration interaction using the Hartree-Fock-Slater atomic model.