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Aufsatz
State-dependent volume isotope shifts of low-lying states of group-IIa and -IIb elements
(1985)
Results of relativistic multiconfiguration Dirac-Fock calculations with an extended nucleus are used to analyze the volume isotope shifts of the resonance transitions in the group-IIa and -IIb elements
as well as in Yb. This is done together with a review of the isotope shift theory, including a critical evaluation and comparison of the semiempirical calculation of volume isotope shifts commonly
used today. Electronic factors F_i, proportional to differences of electronic densities over the nuclear volume, are ...
Aufsatz
Analysis of the electronic structure, hyperfine structure, and volume isotope shifts in the low lying states of BA I and BA II
(1988)
Relativistic multi-configuration Dirac Fock (MCDF) wavefunctions coupled to good angular momentum J have been calculated for low lying
states of Ba I and Ba II. These wavefunctions are compared with semiempirical
ones derived from experimental atomic energy levels. It is found that significantly better agreement is obtained when close configurations are included in the MCDF wavefunctions. Calculations of the electronic part of the field isotope shift lead to very good agreement with electronic factors
derived from ...
Aufsatz
Collision systems
(1984)
Various approximations which are possible for the theoretical description of colliding ion-atom systems are reviewed. With the emphasis on relativistic influences, a few comparisons of experimental results with relativistic calculations are made.
Aufsatz
Accurate Hartree-Fock-Slater calculations on small diatomic molecules with the finite-element method
(1988)
We report on the self-consistent field solution of the Hartree-Fock-Slater equations using the finite-element method for the three small diatomic molecules N_2, BH and CO as examples. The quality of the results is not only better by two orders of magnitude than the fully numerical finite difference method of Laaksonen et al. but the method also requires a smaller number of grid points.
Aufsatz
Study of 3d - 4f and 3d - 5f quartet and doublet transitions of doubly excited three-electron ions
(1989)
We present the first observation of optical transitions between doubly excited doublet states in the term systems N V, 0 VI and F VII. The spectra were produced by foil excitation of fast ion beams. The assignment of the spectral lines was made by comparison with the results of MCDP calculations along the isoelectronic sequence. The same method also led to the identification of two 3d - 4f quartet transitions in Mg X.
Aufsatz
Molecular effects on the cross section for pair production and their importance in the evaluation of the total photonuclear cross section of {^16}O in the {\delta-resonance} region
(1988)
The screening correction to the coherent pair-production cross section on the oxygen molecule has been calculated using self-consistent relativistic wave functions for the one-center and two-center
Coulomb potentials. It is shown that the modification of the wave function due to molecular binding and the interference between contributions from the two atoms have both sizeable effects on the screening correction. The so-obtained coherent pair-production cross section which makes up the largest part of the total atomic ...
Aufsatz
Theoretical study of the structural dependence of nuclear quadrupole frequencies in high-T_c superconductors
(American Physical Society, 1989)
The remarkable difference between the nuclear quadrupole frequencies v_Q of Cu(1) and Cu(2) in YBa_2Cu_3O_6 and YBa_2Cu_3O_7 is analyzed. We calculate the ionic contribution to the electric field gradients and estimate, by using experimental results for Cu_2O and La_2CuO_4, the contribution of the d valence electrons. Thus, we determine v_Q1, v_Q2, and the asymmetry parameter η for YBa_2Cu_3O_6 and YBa_2Cu_3O_7. The number of holes in dthe Cu-O planes and chains is found to be important for the different behavior of ...
Aufsatz
Theory for the Photoacoustic Response to X-Ray Absorption
(American Physical Society, 1988)
A microscopic theory is presented for the photoacoustic effect induced in solids by x-ray absorption. The photoacoustic effect results from the thermalization of the excited Auger electrons and photoelectrons. We explain the dependence of the photoacoustic signal S on photon energy and the proportionality to the x-ray absorption coefficient in agreement with recent experiments on Cu. Results are presented for the dependence of S on photon energy, sample thickness, and the electronic structure of the absorbing solid.
Aufsatz
Transport properties of one-dimensional, disordered two-band systems
(The Institute of Physics, London, 1986)
We have studied the transport properties of disordered one-dimensional two-band systems. The model includes a narrow d band hybridised with an s band. The Landauer formula was used in the case of a very narrow d band or in the case of short chains. The results were compared with the localisation length of the wavefunctions calculated by the transfer matrix method, which allows the use of very lang chains, and an excellent agreement was obtained.
Aufsatz
Autoionization and fragmentation of Na_2 studied by femtosecond laser pulses
(Ed. by Michael S. Feld u.a., 1989)