Energies of 3s and 3p states of sodiumlike ions are calculated from Z=11 to Z=92 starting from a Dirac-Fock potential and including second- and third-order Coulomb correlation corrections, the lowest-order Breit interaction with retardation treated exactly, second- and third-order correlation corrections to the Breit interaction, and corrections for reduced mass and mass polarization. The calculated energies are compared to measured energies to determine the size of the omitted quantum electrodynamics corrections.

The electronic spectrum of the ${\mathrm{T}}_2$${\to }^3$${\mathrm{HeT}}^{+}$+ν¯+$e^{\mathrm{-}}$ β decay is obtained by a Stieltjes-imaging method using Slater and trigonometric basis functions. Except for one strong resonance structure at 68 eV the continuum lacks structure.

The paper examines the extension of the Heisenberg principle for a larger number of simultaneously discussed observables. The possibilities of the extended Heisenberg principle are discussed for evaluation of the average value of the square of the selected operator and for evaluation of the standard deviation of the selected operator.

A formalism recently developed to obtain a matrix representation of the second-order spin-adapted reduced Hamiltonian [J. Karwowski, W. Duch, and C. Valdemoro, Phys. Rev. A 33, 2254 (1986)] and derived from the symmetric-group approach to configuration-interaction methods has been generalized to the case of the third-order spin-adapted reduced Hamiltonian. As in the second-order case, the matrix elements are linear combinations of generalized two-electron integrals with coefficients explicitly related to traces of products of the orbital occupation-number operators. The third-order spin-adapted reduced Hamiltonian matrix has been block diagonalized according to the irreducible representations of the symmetric group $S_3$.

Ab initio Dirac-Fock (DF) and nonrelativistic-limit (NRL) wave functions and dipole moments are calculated to investigate the bonding characteristics and the relativistic effects in the systems ${\mathrm{HgH}}^{+}$, TlH, ${\mathrm{PbH}}^{+}$, and BiH. The dipole moment of AuH is evaluated using the DF self-consistent field and relativistic configuration-interaction wave functions obtained by G. L. Malli and N. C. Pyper [Proc. R. Soc. London, Ser. A 407, 377 (1986)]. Contour plots of relativistic molecular orbital densities and difference density maps are presented to illustrate the arrangement of electronic charge in these systems. It is found that the 5d orbitals are involved in the bonding of ${\mathrm{HgH}}^{+}$, whereas they do not play a significant role in TlH and ${\mathrm{PbH}}^{+}$. The relativistic calculations predict ${\mathrm{HgH}}^{+}$, TlH, and ${\mathrm{PbH}}^{+}$ to be bound. The nonrelativistic-limit wave functions predict ${\mathrm{HgH}}^{+}$ and BiH to be unbound but TlH and ${\mathrm{PbH}}^{+}$ to be bound. It is also found that the calculated dipole moments using the DF and the NRL wave functions for these heavy systems differ significantly in magnitude, and in some cases even in the sign.

First-order many-body theory (FOMBT) has been used to calculate differential cross sections (DCS’s) and electron-impact coherence parameters (EICP’s) associated with excitation of the $n^1$P (n=2,3) electronic states of helium for incident-electron energies in the range 22 eV ≤E≤500 eV. The DCS’s predicted by FOMBT agree reasonably well with the available experimental data and in the 50 eV ≤E≤500 eV energy range, as well as, or better than, those predicted by any other theory. The EICP’s predicted by R-matrix methods are found to agree better with the available experimental data in the threshold region (E≤30 eV) than those predicted by FOMBT. However, in the intermediate-energy region, 50 eV ≤E≤500 eV, FOMBT provides EICP results that are in semiquantitative agreement with the available data. Partial-wave decompositions of the 〈$L_{\perp }$〉 parameter at various incident-electron energies show that the structure observed in this parameter is caused by interference among the free-electron partial waves and that the small-angle characteristics of this parameter are determined principally by low-l partial waves, i.e., by incident electrons with small-impact parameters. Additional experimental measurements and results from more elaborate calculations at intermediate and large scattering angles and for intermediate and high incident-electron energies are needed to resolve a number of issues associated with the interpretation of the EICP’s.

The first measurements of dielectronic recombination rate coefficients associated with the 2s→2p excitation in the B-like ions (${\mathrm{N}}^{2+}$, ${\mathrm{O}}^{3+}$, and ${\mathrm{F}}^{4+}$) are reported. In this case, three levels ${(}^2$D, ${}_{}{}^2{}_{}{}^{}\mathrm{S}$, and ${}_{}{}^2{}_{}{}^{})$ of the excited state exist and are partially resolved. We observed the amount of electron capture attending the passage of MeV/nucleon ion beams through a collinear, magnetically confined, space-charged-limited electron beam as a function of relative energy. The experimental rate coefficients are consistent in magnitude with rates determined from distorted-wave calculations of the dielectronic recombination cross sections.

A distorted-wave Born-approximation method has been used to obtain various results for the electron- and positron-impact excitations of the helium atom initially from its ground (1 ${}_{}{}^1{}_{}{}^{})$ and excited metastable (2 ${}_{}{}^1{}_{}{}^{})$ states to 2 ${}_{}{}^1{}_{}{}^{}P$, 3 ${}_{}{}^1{}_{}{}^{}S$, and 3 ${}_{}{}^1{}_{}{}^{}P$ states. The results are obtained for differential and integrated cross sections. For the 2 ${}_{}{}^1{}_{}{}^{}P$ and 3 ${}_{}{}^1{}_{}{}^{}P$ excitations, coincidence parameters λ and χ as well as the circular polarization $P_3$ are also reported. The correlation effect of the target electrons for the 1 ${}_{}{}^1{}_{}{}^{}$S(2 ${}_{}{}^1{}_{}{}^{}$S)→$2^1$P transition is also considered. Our various results are compared with available previous theoretical and experimental results.

The shock-heated molecular-beam technique was used to obtain vibrationally excited oxygen molecules. The vibrational distributions of these diatomic molecules, in argon gas as the ‘‘carrier’’ gas of a shock-heated molecular beam, have been calculated by considering atomic recombination, collisional excitation, and deexcitation during the expansion. The vibrationally excited molecules, which correspond to vibrational temperatures $T_v$, in the range 1800–7000 K, are used to examine the role played by vibrational excitation in both direct and dissociative electron-impact ionization cross sections over a range of electron energies from 50 to 500 eV. The results show that the dissociative electron-impact ionization cross section increases only slightly with increasing vibrational temperatures, and results agree with the theory based on the modified reflection method.

This paper reports measurements of absolute differential cross sections for elastic and for charge-transfer scattering in ${\mathrm{He}}^{+}$-He collisions. Elastic-scattering cross sections have been determined at 1.5 keV over the laboratory angular range 0.04°–1.0° while charge-transfer cross sections have been determined at 1.5, 2.5, and 5.0 keV over the range 0.02°–1.0°, and at 0.25 and 0.50 keV over the range 0.02°–7.8°. The experimental data exhibit strong oscillations over the range of angles and energies studied and are in agreement with partial-wave theory calculations using phase shifts derived from proposed forms of the gerade and ungerade ${\mathrm{He}}_2^{+}$ interaction potentials. The experimental cross sections have also been integrated over angle to provide absolute integral cross sections.

Absolute differential cross sections for scattering of 0.5-, 1.5-, and 5.0-keV H and He atoms by ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$ over the laboratory angular range 0.05°–0.5° are reported. Charged collision products are not detected, and no determination is made of the energy loss experienced by the scattered projectile. The measured cross sections therefore include both inelastic and elastic processes. The data are in excellent accord with previous measurements of these processes at larger angles. The data have been integrated over angle to permit comparison with other experimental data.

In view of the fact that the mass of the muon is only one-ninth of the mass of the proton, we propose to use a chemical-reaction-theoretical approach to investigate muon (${\mu }^{\mathrm{-}}$) transfer between two nucleons such as d (deuteron), t (triton), and p (proton). In this paper we apply the recently proposed new implementation of the adiabatic approximation (with respect to hindered rotation) to the process dμ+t→d+tμ. Cross sections are calculated at collision energies E≃5–100 eV and are found to be in good agreement with the recent accurate quantum-mechanical calculations at E≲10 eV. This indicates the usefulness of the present approximation.

We have measured the energies ${\mathit{E}}_{\mathit{n}}$ of 6sns ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ (30≤n≤214), 6snp ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ (60≤n≤214), and 6snd ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ (30≤n≤285) Rydberg states of barium with an accuracy of ±60 MHz. For the ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$ series the energy separations $E_{n+1\mathrm{}}$-$E_n$ between neighboring Rydberg states have been deduced with an uncertainty of ±10 MHz. The singlet-triplet splitting between 6snd ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$ states is reported for principal quantum numbers ranging between n=30 and n=190. In addition, we have determined the energies of 6snf ${}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$, 6sng ${}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}$, 6sng ${}_{}{}^3{}_{}{}^{}G$, and 6snh ${}_{}{}^1{}_{}{}^{}H_5^{}{}_{}{}^{}$ Rydberg states at lower principal quantum numbers (47≤n≤78). From our measurements we have deduced quantum defects ${\delta }_l$ of the corresponding 6snl ${}_{}{}^1{}_{}{}^{}L_l^{}{}_{}{}^{}$ Rydberg series to be ${\delta }_0$(n≥50)=4.212(5), ${\delta }_1$(n≥100)=4.332(5), ${\delta }_2$(n≥78)=2.718(5), ${\delta }_3$(47≤n≤78)=0.047(5), ${\delta }_4$(47≤n≤78)=0.059(5), and ${\delta }_5$(47≤n≤78) =0.019(5). The first ionization limit of barium has been determined to be $I_{6s}$=42 034.902(3) ${\mathrm{cm}}^{\mathrm{-}1}$.

The absolute yield of singly and multiply charged ions of krypton and xenon and resulting photoelectron spectra produced by intense laser radiation in the range 285–310 nm are presented. Enhancement of the yield of ${\mathrm{Kr}}^{+}$ by two orders of magnitude in the vicinity of the 4$p^5$4d and 4$p^5$4d’ manifolds is observed at intensities exceeding ${10}^{13}$ W/${\mathrm{cm}}^2$. These observations extend the intensity at which strong resonant enhancement has been observed in multiphoton ionization by two orders of magnitude. A model incorporating line shifts and linewidths scaling linearly with intensity is in good agreement with the experimental results. Absolute cross sections for multiphoton ionization of xenon and krypton are presented and compared with recent theoretical calculations.

Multiconfiguration Hartree-Fock (MCHF) calculations are presented for singlet terms in neutral strontium (Sr i) belonging to (perturbed) sp, sd, and sf Rydberg series. We discuss briefly some particularly difficult MCHF calculations and the steps taken to overcome the difficulties. The ab initio wave functions are used to calculate radiative lifetimes as well as individual transition rates for electric dipole and quadrupole radiation. The calculated lifetimes are compared to recent experimental results. The observed trends are well reproduced by the calculations. We compare our wave functions with wave functions obtained from multichannel quantum-defect theory (MQDT) in either of two different ways. One is based on semiempirical fitting to the observed energy levels and the other on a recent ab initio R-matrix calculation of MQDT parameters. We find good agreement with the wave functions obtained in the latter calculation, confirming earlier conjectures about the degree of reliability of semiempirical MQDT fits to perturbed Rydberg series [C. Froese Fischer and J. E. Hansen, Phys. Rev. A 24, 631 (1981)].

The autoionization rates and energies of the Ba 6$p_{1/2}$nl states for n=11–13 have been measured using a multistep laser-excitation technique. The excitation is via the bound 6snl states which are populated using an electric-field switching method that allows the selective population of the high-angular-momentum states. The results of the measurements indicate an $n^{\mathrm{-}3}$ dependence and a rapid decrease of the autoionization rates with l. For the lowest-l states studied here, l=4, the rates are ≃${10}^{11}$ ${\mathrm{s}}^{\mathrm{-}1}$. At l≃8 the autoionization rates fall below the radiative decay rate of 2×${10}^8$ ${\mathrm{s}}^{\mathrm{-}1}$. Autoionization rates larger than ${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$ are obtained by direct measurements of spectral widths, while smaller rates are determined by a saturation-broadening technique. The autoionization rates are in agreement with calculations based on an nl electron in a hydrogenic orbit around a ${\mathrm{Ba}}^{+}$ core.

The reflection of short optical pulses from the boundary of a resonant medium is investigated theoretically by the coupled system of the Maxwell and optical Bloch equations. In order to describe the reflected wave, the slowly-varying-envelope approximation in space is not exploited. The coherent reflection is shown to be in connection with Dicke superradiance. It takes place if the relaxation time of the polarization is longer than the superradiation time of the atoms in an optically thin boundary layer of the medium. That is why much of the relevant information can be obtained already in the thin-medium limit, which is considered separately. The conditions of strong reflection from an extended medium are similar to the ones found for a thin sample. The transition into the incoherent and stationary regime is discussed.

Multiphoton ionization (MPI) and third-harmonic generation (THG) in xenon and krypton have been studied via three-photon resonance with the xenon 6s’${[1/2]}_1^0$ and krypton 5s${\left[\right(3/2\mathrm{}]}_1^0$ states. A second, tunable dye laser is used to couple these states to higher-lying even-parity states. Observations are reported regarding the third-harmonic related cancellation of the intermediate s-state population and the mechanisms of population of the final states. Effects of the four-photon resonance on THG are detailed. Changes induced by the second laser reduce THG in normally favorable regions and enable it in otherwise forbidden regions. Striking effects in the MPI spectra due to the changes induced in THG are reported.

Diffraction and dispersion effects in Raman scattering are investigated, with focused beams and pump depletion. Power broadening and Stark shifting of the molecular energy levels are included in the equations up to second order in intensity (an intermediate-power approximation). The steady-state paraxial wave equation is used to propagate the electric fields which are expanded in a series of rotationally symmetric Gauss-Laguerre functions. These functions allow diffraction and power-dependent effects to be included quite easily with the introduction of a recursive technique used to evaluate the nonlinear coupling coefficients. The resulting equations are solved analytically for a single transverse mode and numerically for the multimode case. Several examples are given for conversion in ${\mathrm{H}}_2$. In order for the intermediate-power approximation to remain valid, the pump power must be less than 0.015 MW for a beam confocal parameter of 10 cm. Under these conditions we show that power-dependent focusing reduces the Stokes conversion efficiency by a factor of 5 as compared to power-independent focusing.

The basic physics of a slow-wave electron cyclotron maser (ECM) operating in the Cherenkov regime is considered. This device has the advantage over fast-wave ECM’s in that it can be operated with direct axial injection of the electron beam, thus allowing for better control over beam quality and a potentially more compact design. The nonlinear evolution and saturation of the instability are studied using computer simulation. It is shown that high efficiency is attainable and, furthermore, that beam momentum spread is better tolerated in the Doppler-shift-dominated regime than is the case for a fast-wave ECM.