The polarised orbital method for the adiabatic description of low-energy electron/positron-atom scattering is reformulated in terms of a polarised density. The polarised density is expanded into multipoles and the radial functions are treated variationally. This procedure is shown to provide an accurate dipole polarisation potential for e+/e--H scattering. For many-electron targets the quantum statistical Thomas-Fermi energy functional with gradient corrections is used to calculate dipole and quadrupole polarisation potentials. Total elastic cross sections for positron energies below excitation thresholds agree with experiment and with polarised orbital Hartree-Fock calculations for e+-Ne scattering, while the agreement is less satisfactory for e+-Ar scattering.
M Horbatsch et al 1983 J. Phys. B: Atom. Mol. Phys. 16 4451
L Zehnle et al 1978 J. Phys. B: Atom. Mol. Phys. 11 2133
Relative differential cross sections are presented for the collisional excitation of K(4 2P) by He, Ne, Ar, Kr and Xe. The inelastic process is identified by measuring the time correlation between the scattered alkali atom and the emitted photon in a particle-photon coincidence experiment. The measured cross sections are used to identify the curve crossings responsible for the excitation process and to derive the excitation probability as a function of impact parameter.
L Brandus 1969 J. Phys. B: Atom. Mol. Phys. 2 137
A new method for the determination of atomic screening parameters is considered. With the aid of this method the values of screening parameters are determined for the ground state and some excited states of He-Ne atoms.
D A Andrews and G Newton 1978 J. Phys. B: Atom. Mol. Phys. 11 603
A formal solution is presented for an atom which is simultaneously in static and oscillatory electric fields. This is used to calculate the amplitudes of m-quantum resonances in two- and three-level atoms. These results are compared with experiment for the n=2 manifold in atomic hydrogen.
C K Au 1984 J. Phys. B: Atom. Mol. Phys. 17 L59
The wavefunction of a quantum mechanical system can be evaluated in any gauge and can be expressed in terms of a complete set of eigenstates of a physical observable or of a mathematical operator. If the physical observable is expressed in the same gauge as the Hamiltonian from which the wavefunction is obtained, the expansion coefficients are gauge invariant and have definite experimental implications. This physical observable need not be the energy. If the basis set of vectors are eigenstates of a mathematical operator, the expansion coefficients are gauge dependent. This mathematical operator can be translated to a physical observable once the gauge under which the wavefunction is calculated is specified. The expansion coefficients can then be interpreted as probability amplitudes.
D Richards and M R C McDowell 1972 J. Phys. B: Atom. Mol. Phys. 5 1811
It is shown that the Coulomb T matrix satisfies a dispersion relation off-shell. In the half on shell case (k2=k12 not=k22 or k2=k22 not=k12) this provides an unambiguous definition for the imaginary part in terms of a generalized function. A subtractive procedure is introduced to extend these results to the real part.
R Francois et al 1972 J. Phys. B: Atom. Mol. Phys. 5 963
Elastic and inelastic differential measurements of the Li+-He system were undertaken with particular attention given to the charge exchange channels. The energy variation of the 'summed' differential cross sections (elastic, inelastic and change exchange) agrees quite well with the published ab initio ground state calculation, showing that most important channels are considered. All the inelastic and charge exchange processes are discussed in the frame of the diabatic correlation diagram.
G Wunner et al 1983 J. Phys. B: Atom. Mol. Phys. 16 2937
It is proved that in magnetic fields B>or approximately=107 T, which are characteristic of neutron stars, the lifetime of an electron in an excited Landau level (N>or=1) bound to a proton becomes identical to that of an electron moving freely along the magnetic field lines, viz. the lifetime with respect to cyclotron transitions. The associated widths are found to be larger than or at least comparable with the Coulomb binding energies (depending on the magnetic field strength) whence the nature of these states as discrete states is obliterated. The authors show that the anomalous magnetic moment of the electron and the finite mass of the proton cause additional level shifts comparable in magnitude with the Coulomb energies. Furthermore, they investigate thermal line broadening and find that, as a consequence of the pronounced anisotropy of the effective masses for motion parallel and perpendicular to the field, thermal broadening is strongly reduced for emission perpendicular to the field.
N Andersen et al 1978 J. Phys. B: Atom. Mol. Phys. 11 L493
Energy losses are measured for 1.5-3.5 keV Ne+ ions scattered by D2 through angles out to 5 degrees. The results show that the effective scattering mass of a molecule is a function only of the reduced scattering angle tau =E theta , in agreement with a recent scaling theorem by Sigmund (1978).
M Kimura and W R Thorson 1983 J. Phys. B: Atom. Mol. Phys. 16 1471
The authors have performed molecular-state close-coupling calculations of charge transfer cross sections for collisions of the fully-stripped ions Li3+, Be4+ and B5+ with H(1s) atoms at low to intermediate projectile energies (1 to 15 keV amu-1). Translation factor effects were included using molecular-state switching functions as in previous studies. Calculations with basis sets of different sizes were done for each system to provide a rough estimate of convergence. The results are compared with other theoretical calculations and with available experiments.
U Wille 1987 J. Phys. B: Atom. Mol. Phys. 20 6669
M Kimura et al 1987 J. Phys. B: Atom. Mol. Phys. 20 6670
N N Choi et al 1987 J. Phys. B: Atom. Mol. Phys. 20 L827
Non-relativistic rates for the decay of 2s hydrogen atoms to the ground state by single-photon and two-photon emission in the presence of a homogeneous magnetic field of arbitrary strength (0<or=B<or=4.7*106 T) are calculated by variational procedures. Over the whole range of B, two-photon emission is the dominant process. As the magnetic field grows, the two-photon decay rate increases. It is found that the Markov approximation can be applied to the two-photon decay for magnetic fields of strength B>or=4.7*103 T.
B Wallbank et al 1987 J. Phys. B: Atom. Mol. Phys. 20 L833
Differential cross sections for the one-photon emission free-free process are measured as a function of laser intensity when 10.55 eV electrons are scattered from argon atoms in the presence of a pulsed CO2 laser. The cross sections are reported for both single longitudinal-mode and multimode laser pulses up to an intensity of 2*107 W cm-2. For intensities less than 2*106 W cm-2, the cross sections for both laser pulses are found to be linear with intensity, in agreement with perturbation theory. At higher intensities comparisons are made with predictions based on the low-frequency approximation and two laser models. The linear parts of the cross sections are used to obtain estimates of the spatial inhomogeneities in the electron-laser interaction region. Reasonable agreement is found between the experimental cross sections and those predicted by the two laser models.
Y Vitel and M Skowronek 1987 J. Phys. B: Atom. Mol. Phys. 20 6477
Stark widths and shifts of the Ar I 696.5 nm and of the Ar II 480.6, 484.7 and 434.8 nm lines have been measured in the range of electron density and temperature 0.6-1.5*1018 cm-3, 16200-18700 K. These high-density plasmas are created in linear flash-tubes. The plasma parameters are principally determined by measurements of the continuum radiation, from the intensity of optically thick lines in their centre and by the condition of local thermodynamic equilibrium of the plasma. The electron density and temperature radial profiles so deduced are found to be practically flat over more than half of the tube radius. In this quasi-stationary stage of the plasma, the experimental line profiles are recorded by an optical multichannel analyser coupled with a high-dispersion spectrometer. The profiles are analysed and fitted to a Lorentzian function. The Stark parameters, width and shift, show a non-linear dependence against the electron density.
B E J Pagel 1971 J. Phys. B: Atom. Mol. Phys. 4 279
The following applications of spectral line broadening theory to astrophysics are briefly reviewed: (i) understanding qualitative effects visible on spectrograms; (ii) quantitative understanding of hydrogen-line profiles for the determination of stellar atmospheric parameters; (iii) effects of line broadening on the determination of stellar chemical composition.