{2p_\pi}-{2p_\sigma} crossing in heavy symmetric ion-atom collisions: I. Level structure

Ab initio self-consistent DFS calculations are performed for five different symmetric atomic systems from Ar-Ar to Pb-Pb. The level structure for the {2p_\pi}-{2p_\sigma} crossing as function of the united atomic charge Z_u is studied and interpreted. Manybody effects, spin-orbit splitting, direct relativistic effects as well as indirect relativistic effects are differently important for different Z_u. For the I-I system a comparison with other calculations is given.

Electronic structure calculations of small AI_n (n = 2 - 8) clusters

The electronic states of small AI_n (n = 2 - 8) clusters have been calculated with a relativistic ab-initio MOLCAO Dirac-Fock-Slater method using numerical atomic DFS wave-functions. The excitation energies were obtained from a ground state calculation of neutral clusters, and in addition from negative clusters charged by half an electron in order to account for part of the relaxation. These energies are compared with experimental photoelectron spectra.

Influence of occupation number of single particle levels on K - K charge transfer in collisions of 90 keV - Ne{^9+} on Ne

The influence of the occupation of the single particle levels on the impact parameter dependent K - K charge transfer occuring in collisions of 90 keV Ne{^9+} on Ne was studied using coupled channel calculations. The energy eigenvalues and matrixelements for the single particle levels were taken from ab initio self consistent MO-LCAO-DIRAC-FOCK-SLATER calculations with occupation numbers corresponding to the single particle amplitudes given by the coupled channel calculations.

Inclusive probabilities for the scattering system 16 MeV-S{^16+} on Ar

We performed ab initio calculations of many particle inclusive probabilities for the scattering system 16 MeV-S{^16+} on Ar. The solution of the time-dependent DIRAC-FOCK-SLATER-equation is achieved via a set of coupled-channel equations with energy eigenvalues and matrix elements which are given by static SCF molecular many electron calculations.

Application of inclusive probability theory to heavy ion-atom collisions

Using the independent particle model as our basis we present a scheme to reduce the complexity and computational effort to calculate inclusive probabilities in many-electron collision system. As an example we present an application to K - K charge transfer in collisions of 2.6 MeV Ne{^9+} on Ne. We are able to give impact parameter-dependent probabilities for many-particle states which could lead to KLL-Auger electrons after collision and we compare with experimental values.

Study of 3d - 4f and 3d - 5f quartet and doublet transitions of doubly excited three-electron ions

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.

Influence of the interaction potential on simulated sputtering and reflection data

The TRIM.SP program which is based on the binary collision approximation was changed to handle not only repulsive interaction potentials, but also potentials with an attractive part. Sputtering yields, average depth and reflection coefficients calculated with four different potentials are compared. Three purely repulsive potentials (Meliere, Kr-C and ZBL) are used and an ab initio pair potential, which is especially calculated for silicon bombardment by silicon. The general trends in the calculated results are similar for all potentials applied, but differences between the repulsive potentials and the ab initio potential occur for the reflection coefficients and the sputtering yield at large angles of incidence.

Relativistic prediction of the ground state of atomic Lawrencium

In contradiction to the prediction of the Periodic Table but in agreement with earlier suggestions by Brewer and Mann, the ground state configuration of atomic Lawrencium (Z = 103) will not be 7s^2 6d^2 D_3/2 but 7s^2 7p ^2p_1/2. The reason for this deviation from normal trends across the Periodic Table are strong relativistic effects on the outermost 7P_l/2 orbital. Multicontiguration Dirac-Fock calculations are reported for Lawrencium and analogous lighter atoms. These calculations include contributions from magnetic and retardation interactions and an estimation of quantum electrodynamic corrections.

Relativistic atomic level calculations with nuclei carrying additional fractional charges

One-electron energy levels and wavelengths have been calculated for Na-like ions whose nuclei carry quarks with additional charges ±e/3, ±2e/3. The calculations are based on relativistic self-consistent field procedures. The deviations from experimental values exhibit regularities which allow an extrapolation for the wavelengths of 3s - 3p, 3s - 4p, 3p - 3d, and 3p - 4s transitions for the nuclear charge Z = 11± 1/3, ±2/3. A number of transitions are found in the region of visible light which could be used in an optical search for quark atoms.

Finite element method for the accurate solution of diatomic molecules

We present the Finite-Element-Method (FEM) in its application to quantum mechanical problems solving for diatomic molecules. Results for Hartree-Fock calculations of H_2 and Hartree-Fock-Slater calculations of molecules like N_2 and C0 have been obtained. The accuracy achieved with less then 5000 grid points for the total energies of these systems is 10_-8 a.u., which is demonstrated for N_2.

Atomic and ionic radii of superheavy elements

Atomic and ionic radii are presented for the elements E104-E120 and E156-E172. It is shown that a number of effects correlated with the large relativistic contraction of orbitals with low angular momentum leads to smaller atoms for higher atomic numbers. It is expected that Cs is the largest atom in nature.

Electronic configuration in the ground state of atomic lawrencium

Self-consistent relativistic Dirac-Hartree-Fock calculations have been made of some lowlying electronic energies for the atoms of all elements in ground-state ds^2 electron configurations. The results indicate that, contrary to some previous estimates, the ground electronic state of atomic Lr could be in either the 5f^14 6d7s^2 or the 5f^14 7p 7s^2 electron configuration. The separation between the lowest energy level of the 5f^14 6d7s^2 configuration and the lowest energy level of the 5f^14 7p7s^2 configuration is estimated to be (0 ± 3) x 10^3 cm^-1 for atomic Lr.

Observation of two-electron-one-photon transitions in silicon

We report on the observation of K\alpha\alpha X-rays of Si, produced in collisions of 15-28 MeV Si projectiles with various target atoms in the range Z =6 to 29. Energy shifts of X-rays were measured and are compared with theoretical predictions. Cross section ratios for emission of K\alpha\alpha and K\alpha radiation are given.

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

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 cross section was used to evaluate the total nuclear absorption cross section from photon attenuation measurements on liquid oxygen. The result agrees with cross sections for other nuclei if A-scaling is assumed. The molecular effect on the pair cross section amounts to 15 % of the nuclear cross section in the {\delta-resonance} region.

Time-resolved studies of neutral and ionized Na_n clusters with femtosecond light pulses

The real-time dynamics of Na_n (n=3-21) cluster multiphoton ionization and fragmentation has been studied in beam experiments applying femtosecond pump-probe techniques in combination with ion and electron spectroscopy. Three dimensional wave packet motions in the trimer Na_3 ground state X and excited state B have been observed. We report the first study of cluster properties (energy, bandwidth and lifetime of intermediate resonances Na_n^*) with femtosecond laser pulses. The observation of four absorption resonances for the cluster Na_8 with different energy widths and different decay patterns is more difficult to interpret by surface plasmon like resonances than by molecular structure and dynamics. Timeresolved fragmentation of cluster ions Na_n^+ indicates that direct photo-induced fragmentation processes are more important at short times than the statistical unimolecular decay.