A theoretical study, at three levels of approximation [self-consistent field (SCF), multiconfiguration (MC)-SCF, and extensive configuration interaction CI of the valence electrons] is reported for the ${\mathrm{Cu}}_2$ system. In spite of the great improvement of the total energy for the system obtained with the MC-SCF and CI methods, the predicted bond length is too long. Some discussion on the possible causes of this disagreement with experimental equilibrium distance is given.

A recently proposed complex stabilization method is examined from the viewpoint of the necessity for an explicit construction of the coordinate-rotated Hamiltonian. It is demonstrated and proved that the argument for using unrotated Hamiltonians in resonance-structure determinations must be taken in a restricted sense. With the use of square-integrable basis functions, it is shown that complex rotation is necessary to directly calculate complex resonance poles. We illustrate our conclusion by a numerical model calculation.

It is observed in the Duffing oscillator that a bifurcation from a solution composed of only odd harmonics to one composed of both even and odd harmonics precedes the period-doubling bifurcations. Keeping all parameters fixed except for the amplitude of the driving force $F$, we determine the value of $F$ at which the bifurcation occurs. Results are compared with experiment. A mechanism for the period-doubling bifurcations is suggested.

Using a Fano-effect polarized electron source and a state-selected thermally dissociated hydrogen beam, we measured the interference between the direct and exchange scattering amplitudes for electron-impact ionization of atomic hydrogen between 14.1 and 30.3 eV. We report the data from these measurements and the results of corrections applied to previously published data.

Close-coupling charge-exchange calculations for ${\mathrm{C}}^{6+}$-H collisions have been carried out for impact velocities spanning 2.5×${10}^4$ to 5×${10}^5$ m/s (∼3-to-1300—eV H energy). Six appropriate molecular states were included, among which all radial and angular couplings were evaluated using the proton as an electronic origin following the approach of Piacentini and Salin. Four levels of semiclassical approximations for the nuclear motion were investigated and compared: (1) the usual straight-line impact-parameter approximation, (2) the use of a Coulomb trajectory on a effective $\frac{6}{R}$ potential, (3) the previously developed average approximation, which is a form of multitrajectory theory, and (4) a uniform semiclassical reference-function method of essentially full quantum accuracy. The results are presented and the validity of these various approximations for the nuclear motion is discussed, for the range of collision energies reported.

Semiempirical screening parametrizations are used to specify accurately the fine-structure separations of the ${}_{}{}^2{}_{}{}^{}P$ ground states in the boron and fluorine isoelectronic sequences.

More convenient formulas are given for the angular distribution and spin polarization of photoelectrons including all multipole transitions.

Using Lin's Microscopic theory for the isotropic-nematic transition, we propose a new explanation for earlier experimental results where deviations of the optical Kerr constant of nematogens from the mean-field behavior were observed several degrees above the transition.

Calculations of the spectrum of synchrotron emission parallel to a magnetic field are presented for relativistic loss-cone-type distribution functions in the tenuous-plasma limit. Substantial deviations from the result for an isotropic Maxwellian are obtained.

The long-time properties of biased diffusion in media with randomly distributed traps is discussed. For any bias the asymptotic decay is exponential, contrary to the unbiased case. We find a sharp transition between a small-bias behavior, for which particles are effectively localized, and a large-bias behavior, for which the particles drift with the bias.

The recent paper by Pitchford and Phelps raises a number of questions concerning the electron velocity distribution and transport and rate coefficients in (molecular) gases. In this paper we will present some of our related Monte Carlo simulation results as a contribution to the solution of the open problems.

Recent measurements of electron mobilities in hydrogen and nitrogen by Freeman and Wada [Bull. Am. Phys. Soc. 25, 1114 (1980); Phys. Rev. A 24, 1066 (1981)] have led these authors to propose Ramsauer-Townsend minima in the cross sections for $e$-${\mathrm{H}}_2$ and $e$-${\mathrm{N}}_2$ scattering. Examination of existing experimental and theoretical data for these systems strongly suggests that such structures are not present in these gases. It is argued that a temperature-dependent systematic error in the measurements of Freeman and Wada may be responsible for the appearance of minima in their cross sections.

$K$-shell vacancy fractions have been measured for 2.7- and 0.4-MeV nitrogen ions exiting from thin carbon foils as a function of foil thickness. The vacancy fractions per projectile ion were deduced from measuring the yields of $K$-Auger electrons emitted by the foil-excited nitrogen ions. It is found that the vacancy fractions for these ions reach equilibrium only for foils thicker than ∼20 μg/${\mathrm{cm}}^2$. The variation of vacancy fractions in foils with thicknesses below 20 μg/${\mathrm{cm}}^2$ is a strong function of the projectile energy.

The omission of a class of beam modes by Pattanayak and Agrawal is rectified, and the relationship of the representation of electromagnetic beams used by them to that used by the present authors is clarified.

The cross section for scattering by a Coulomb potential, cut off at large distance, in the presence of a low-frequency laser field, is obtained as a power series in the laser frequency. The long-range nature of the potential introduces a change in the leading term (${\omega }^0$) as well as a new term proportional to $\omega \ln \omega$. It is also found that the Coulomb cutoff parameter can, under some circumstances, become an observable.

Molecular-structure calculations have been performed to obtain the adiabatic potentials for ground-state and excited NaHe and CsHe systems. They use $l$-dependent pseudopotentials for $e$-He and $e$-${\mathrm{Na}}^{+}$ (or ${\mathrm{Cs}}^{+}$) interactions. The adiabatic potentials obtained for the low-lying states of NaHe and for some excited states of CsHe are in good agreement with recent experimental data, indicating a large improvement on all previous calculations for these systems.