Table of contents

The wavelengths and isotope shifts of the B III resonance lines and have been measured with a Fourier transform spectrometer and a Penning discharge source. The wavelength uncertainty is estimated as and for the and components, respectively. The isotope shift is found to be or for both lines.

The semiclassical molecular orbital approximation modified by a proper electron translation factor has been employed to investigate the dynamics of the low-energy charge transfer between molecular hydrogen and a few stripped ions having charges . Freezing the molecular details of the target the colliding system has been treated as a quasi-diatomic molecule using the pseudo-potential technique that accounts for the effective binding of the electron in the combined nuclear field. Close-coupled equations are solved to obtain both the total and partial capture cross sections. The calculated total cross sections show good agreement with the available experimental measurements; the reported -distributions for and are new. A relative comparison for single-electron transfer from by other ions considered reveals the possible role of the projectile core; in the low-energy region the increasing core size affects considerably both the -distribution and the shape of the total capture cross sections. The projectile exhibits a distinctive role due to its finite core; the calculated total cross sections show oscillations in complete agreement with the experimental findings. The presence of a finite core enhanced the contribution to the lower -value substate of the final channel in accordance with the role of the Stark effect; the state-selective capture cross sections depend strongly on the size of the projectile core.

We report measurements at relativistic electron energy (300 keV) on the K shells of silver and gold . Using coplanar asymmetric kinematics the angular distributions of the relative triply differential cross sections were measured. They are compared with results obtained using the relativistic distorted-wave Born approximation. For gold we find that the recoil peak is of the same order of magnitude as the binary peak. This is in good agreement with the theory which predicts a strong increase of projectile - nucleus interaction with increasing atomic number.

This work reports Stark shifts and widths of 15 Ar I lines measured in a pulsed arc. Plasma parameters, electron density and temperature, range in this experiment from 0.25 to and from 13 500 to 26 500 K, respectively. The former has been measured interferometrically at a single wavelength and spectroscopically from the -Stark broadening. The latter has been measured from the Boltzmann plot of Ar II lines and from the ratio of Ar II and Ar I line intensities. Comparisons with most of the data published to date about this topic in Ar I are also included.

The argon broadened profiles of two ytterbium lines which form a stepwise excitation route -- are reported. The red and blue far wing features are discussed and qualitative information on the argon-ytterbium potentials are obtained. It is shown that the system is suitable for a two-step redistribution experiment.

The VUV spectroscopic study of -particle-excited neon-krypton mixtures showed the occurrence of intense energy transfers from neon to krypton. The spectra of mixtures containing a few per cent krypton are similar to those of pure krypton. They are dominated by krypton's second continuum centred at 148 nm, its intensity increasing with the krypton concentration and the total pressure. Furthermore, a low-intensity emission due to the heteronuclear ion situated at 166.5 nm was also observed. The kinetic study of the second continuum of krypton revealed that heteronuclear reactions play an important role in the formation of at low krypton partial pressures. Their reaction constants were found to be for the state and for . Under high krypton pressures, homonuclear reactions were dominant, the reaction constant being for the state and for .

A theoretical analysis for doubly differential cross sections of the single ionization of helium by proton impact as a function of the scattering angle and projectile energy loss is presented. We have used two different theoretical methods. The first approach involved an approximate solution of Faddeev-Merkuriev equations for the three-body Coulomb problem. The second approach employed the expansion of the transition amplitude in the Born series over the projectile-target interaction up to second order. A relation between these two methods was established for the case of fast collisions. It has been demonstrated that, for small scattering angles, the post-collision interaction in the final state between the charged particles strongly influences the differential cross sections, whereas double-scattering mechanisms dominate for scattering angles mrad. The results of our calculations are in a good agreement with the measurements of Schulz et al for 50-150 keV collisions.

For single ionization of He atoms in collisions with fast protons we have measured and calculated, as a function of the scattering of the proton, differential reaction cross sections and mean values of the recoil momentum projected onto the transverse direction defined by the collision plane and the plane perpendicular to the proton impact velocity (the mean transverse momentum). The calculations were performed in the continuum distorted-wave eikonal initial-state (CDW-EIS) approximation. The partitioning, at a fixed scattering angle , of the total transverse recoil momentum into two mean transverse momenta, one carried by the free electron and the other by the remaining ion, is almost independent of the impact energy (250, 500 and 1000 keV). At the mean transverse electronic momentum goes to zero, but for the fraction rises smoothly and reaches 80% near 0.4 mrad. The present experimental cross sections and transverse recoil momenta are in good agreement with CDW-EIS results including the internuclear interaction.

Differential cross sections (DCS) for the elastic scattering of electrons have been measured by the crossed-beam technique for CO, , , H and H in the angular range - and at impact energies of 300, 500, 700, 900, 1100 and 1300 eV. The measurements were made with a view to test the validity of the independent atom model (IAM) for polyatomic molecules in this energy region. A comparison of experimental results with the IAM calculations indicates that the model is adequate for the linear molecules CO and in the energy region 900-1300 eV. The Born approximation for the evaluation of the atomic scattering amplitudes was found to be valid only at 1300 eV for all the molecules except for H. A survey of the previous experimental and theoretical data based on different models shows that proper molecular wavefunctions have to be used for the evaluation of short-range potentials and that valence-bond distortion, absorption and non-adiabatic effects in the polarization potential have to be considered.

Ab initio cross section calculations using the R-matrix approach have been performed for the inner-shell photoabsorption of atomic oxygen in the photon energy region 520-555 eV. The prominent (1s2(P)np ) resonance series, converging to the series limit of atomic oxygen, dominate the cross section in the vicinity of the K-edge. A comparison of the calculations with two recent sets of experimental measurements taken at the Advanced Light Source and at the Wisconsin synchrotron facility is made.

The R-matrix method is used to calculate electron scattering cross sections for the excitation of four low-lying electronically excited states of the water molecule. These states, of symmetry , , and , have vertical excitation energies in the range 7-10 eV and are known to be dissociative. Resonances, corresponding to dissociative states of the anion, are found in the , and symmetries at energies in excellent agreement with the results of dissociative attachment experiments. Integrated cross sections are given for scattering energies up to 20 eV

A frozen-core model of atomic silver is developed with the core consisting of the 1s to 4d shells. The model is validated by predictions of the electron affinity and binding energies of neutral Ag. The model predicts the existence of an electronically stable ground state of with a binding energy of and a spin-averaged annihilation rate of . The properties of a number of other positronic atoms are studied and it is seen that there is a general tendency for the annihilation rate to decrease as the ionization potential of the parent atom increases.

We present non-adiabatic simulations of the excitation and de-excitation of an sodium cluster irradiated by intense femtosecond lasers. Both electronic and ionic degrees of freedom are explicitly accounted for, whatever nonlinear regime is accessed. We find that the Coulomb fragmentation of the thus excited cluster depends sensitively on the laser frequency. We furthermore show that in the first 100 fs following the laser excitation, ionic degrees of freedom can safely be considered to be frozen. They then couple quickly to the electronic ones, within about another 100 fs, well before electronic excitation has fully levelled off.

An explanation is presented for the recently reported striking differences in the kilovolt Xe L-shell x-ray emission from Xe cluster targets excited by comparable terawatt ultraviolet (248 nm) and infrared (800 nm) femtosecond laser pulses under nearly identical experimental conditions (Kondo K et al 1997 J. Phys. B.: At. Mol. Opt. Phys. 30 2707-16). A classical analysis of these results, within the framework of the first Born approximation for electron-atom collisions producing inner-shell ionization, strongly suggests that both the times stronger Xe(L) emission under ultraviolet laser excitation and the observed differences in the x-ray spectra are caused primarily by the different ultraviolet and infrared pump laser wavelengths. The kinematics of photoionized electrons in the intense laser fields (-) and the Coulomb-driven expansion of the electron distribution photoionized from the atomic cluster both indicate that the strong pump-laser wavelength scaling in the production of kilovolt x-rays from Xe clusters results from the more localized and controlled electron-cluster interactions afforded by a shorter optical period.