Table of contents

Discrete variable representations (DVRs) with underlying trigonometric bases are discussed. A new cosine basis is introduced, and the corresponding DVR is derived. The polynomial origins of a sine basis DVR derived by Baye (1995 J. Phys. B: At. Mol. Opt. Phys. 28 4399) is presented.

A `masking' effect in the photoelectron angular asymmetry -parameter spectrum is discovered and exemplified by calculations of the and giant neighbouring autoionizing resonance structures in of the ) ion. The effect results in the fine-structure resonances, well developed for the for each of the three final j-states, being smoothed out, i.e. `masked' in a total spectrum of , where the individual j-states are unresolved. Also the ion turns out to be the first example showing `q-reversal' and `width narrowing' effects in the -parameter spectrum, which were recently predicted. The `spin-polarized' random-phase approximation with exchange was used in the present calculations.

We present first results for excitation - ionization of helium satellite lines above the double-ionization threshold using the hyperspherical close-coupling (HSCC) method. The ratio for excitation of the satellite line to the main line (i.e. n = 1) is calculated over a wide range of energies from near the double-ionization threshold to energies above which perturbation methods are expected to be more suitable. Comparison with very recent experiments of Wehlitz et al shows excellent agreement for all satellite lines of n = 2,3,4 as well as for the angular distribution asymmetry parameter .

A time-dependent numerical analysis is made of atomic wavefunctions evolving under the influence of laser pulses sufficiently intense that relativistic effects are important. The investigation utilizes the two-dimensional Dirac equation to identify relativistic effects such as the contribution of the magnetic field and spin dynamics.

Recent progress in experimental and computational methods for the study of negative atomic ions has greatly improved the knowledge about the structural and dynamic properties of the negative alkaline-earth ions. This review deals in particular with the stable ground states in , , and and with the metastable quartet states (, , and ) observed in , , , and . Future perspectives are discussed.

Results from systematic multiconfiguration Hartree - Fock studies of the - transitions in the Be-like sequence in the range of Z = 4 - 10 are reported for valence and core-valence models of correlation. The inclusion of core - valence correlation was essential for obtaining good agreement for the fine-structure splitting. The most accurate transition rates are in good agreement with the rates predicted from a semi-empirical analysis of experimental data.

A theory of electronic resonances based on spin-coupled wavefunctions is presented. The formulation is state selective and yields the best single-configurational minimax wavefunctions for resonance closed channels. The theory is demonstrated by calculations of positions, shifts and widths of resonances of a test system, s-wave helium.

The optical isotope shifts in the transition - of Nd II were measured by using collinear fast-ion-beam laser spectroscopy. The changes in mean-square nuclear charge radii among five even - even neodymium isotopes were deduced from the measured optical isotope shifts: (142,144) 0.269; (144,146) 0.259; (146,148) 0.278; (148,150) 0.403. The configuration admixtures of the previously unclassified level were quantitatively analysed to be , , and with mixing probabilities of 13%, 85%, 2%, respectively.

Stark width tables of the Paschen alpha line in hydrogen plasmas are presented, as an aid for plasma diagnosis. The calculations have been carried out by means of a computer simulation technique using particles and within the usual framework of a - ion model. With this technique, an adequate treatment of the ion dynamics effects can be achieved. The calculations cover a range of electron densities between - and temperatures that go from 5000 to 40 000 K. Four values of the reduced mass of the emitter - perturber pair have been considered, and 2.0.

As part of a systematic quantitative study of the angular dependence of valence-shell electron-impact excitation of molecules, we have determined, for the first time, the absolute inelastic differential cross section and the generalized oscillator strength (GOS) for the transition (5.2 eV) in anthracene . A minimum in the GOS has been observed at a value of around 0.2 au. The GOS values were determined from the relative inelastic differential cross section, measured with an electron-impact spectrometer, which uses a Wien-filter velocity analyser. The incident electron energy was 1 keV, the energy resolution was 1.0 eV and the energy-loss spectra were obtained in the range of - . The absolute elastic differential cross section was determined in the - angular range.

Calculations of the angular distribution of the photoelectron ejected from the 2p subshell of the state of , Li and have been performed using multi-configuration Hartree - Fock (MCHF) wavefunctions. The angular distribution asymmetry parameter for is in excellent agreement with previous theoretical calculations and experimental measurements. The corresponding results for Li and , which have not been explored previously, increase from threshold to maximum values first and then decrease monotonically as the photoelectron energy increases. The results are explained in terms of the dipole transition matrix elements and the phase shifts.

The interference phenomena which can take place at the negative ion photodecay in a bichromatic electromagnetic (EM) field of linear and circular polarization consisting of coherent superposition of commensurable th and th harmonics of the same fundamental field are studied within the confines of the theory of perturbation on EM interaction and a zero-range potential model for the negative ion. The case of both odd and and that of odd and even (or vice versa) have been considered. It has been shown that, in the first case, the angular distribution of the emitted photoelectrons is always completely polar symmetric (in respect of the replacement , here p is the photoelectron momentum) and that the total photodecay probability is a periodic function of phase shift between harmonics. However, in the second case of odd and even , the angular distribution has polar asymmetry the degree of which depends on the values of and ratio of the electric vector strengths of the harmonics. Unlike the first case however, the total photodecay probability does not depend on phase shift at all. Moreover, the importance of taking into account the intermediate intercontinuum EM transitions (accompanied with the photoelectron momentum and energy change) has been shown too.

A physically correct introduction of a cross section for the excitation of autoionization states into the theory of resonant ionization is considered and the relation of this quantity to measurable values is discussed. Excitation cross sections have been shown to differ from resonance yields even for isolated resonances without any post-collision interactions, so that this difference might be used to study the interplay of various atomic interactions in ionization processes. Numerical results for helium ionization by charged-particle impact in a broad range of velocities are presented in support of the conclusions made. It has been found that the resonance yield can provide a lower estimate for an excitation cross section for asymptotic collision velocities.

The non-dissociative single-ionization cross section for 40 - 1000 keV antiproton impact on molecules has been measured. Furthermore, the ratio between the production of and ions was obtained. The experimental results agree qualitatively with similar data obtained previously for other molecular targets, and support the `standard picture' of ionization that has emerged during the last decade after much experimental as well as theoretical work on ionization caused by particles and their antiparticles.

We present a method for evaluating arbitrary higher-order derivatives of the three-denominator Lewis integral frequently encountered in collisional and structural problems of atomic and molecular physics. The method has been applied successfully to obtain analytical expressions for the charge transfer amplitude in proton - hydrogen collisions and the results for total cross sections in Jackson - Schiff (JS) and distorted-wave approximations (DWB) are presented.

Elastic cross sections for electron scattering off cyclopropane are calculated employing the R-matrix formalism. Calculations are reported both within the static exchange approximation and when electron correlation is included at the static exchange plus polarization level. The experimentally observed resonance in symmetry at 5.5 eV is reproduced. The computed energy position of the resonance is found to be sensitive to the level on which electron correlation is taken into account. Differential cross sections are calculated and compared with experimental results.

In the perturbation series treatment of scattering, the effect of atomic polarizability first appears in the second-order term. Consequently, the atomic polarizability does not contribute to the scattering amplitudes in the usual first-order distorted-wave treatment without making approximations. However, it is known that this effect is important and including it in a first-order treatment is desirable. This paper investigates different methods for including the effect of polarizing the target atom in a first-order treatment for electron - hydrogen scattering. In particular, we examine approximations for including the effect of atomic polarizability on the projectile wavefunction as well as the effect of distortion of the atomic wavefunction. For the latter case, we approximate the polarized atomic states as Stark states, and have used these states for both the determination of the final-state potential and the evaluation of matrix elements. The accuracy of the various methods is ascertained by comparing their results with those obtained from a second-order distorted-wave Born approximation using the real part of the Green's function. The results also are compared with available experimental data for electron - hydrogen scattering.

Experimental and theoretical values of the Stokes parameters are reported for electron impact excitation of the state of helium at 30 eV. The theoretical results are from a 111-state convergent close-coupling (CCC) method. Excellent agreement is obtained between theory and experiment for the Stokes parameters and for the derived parameters describing the shape and dynamics of the excited state. By considering the excitation as the incoherent sum of two coherent processes, an ambiguity in constructing the excited state from the experimental dipole radiation pattern is removed. This provides an attractive way of providing a complete description of the excitation compared with a triple coincidence experiment involving the scattered electron and photons from the 3D - 2P - 1S transitions. This analysis is also carried out for the state at 30 eV and comparison is made between 111-state CCC calculations and the experimental data of Donnelly et al.

Superelastic scattering of electrons from excited atoms is the time-reverse of inelastic scattering and hence the scattering amplitudes for these two processes are directly related. However, present inelastic experiments are unable to resolve the hyperfine-structure states of the excited atom, whereas in superelastic experiments the atoms are usually prepared in a particular hyperfine state by optical pumping. Thus, care must be taken when comparing the results from one type of experiment with another and with theoretical calculations to ensure the comparison is valid in the given circumstances. In this paper we derive a theoretical mechanism by which inelastic scattering amplitudes can be used for the calculation of superelastic scattering parameters for alkali atoms which have been laser excited to specific hyperfine-structure states of the multiplet where the magnitude of is at its maximum value of (I is the nuclear spin). We have found that when using unpolarized electrons the Stokes parameters for this superelastic case are extremely similar to the analogous parameters for inelastic scattering even when relativistic effects are strong. We also introduce superelastic generalized Stokes parameters and give numerical values for these using a relativistic distorted-wave method.

Electron spectra from 20 and 50 keV - Ne and 25, 40, 50, and 60 keV - Ne collisions have been measured at ejection angles of 20 - , and at electron energies down to 1.6 eV. In both collision systems, a low-energy structure is observed at energies below 5 eV superimposed on a broad continuum. It is proposed that the low-energy structure may be due to electrons promoted to the continuum via the so-called T promotion associated with `saddle-point' electrons.

A theory of the post-collision interaction (PCI) is developed for the case when an electron - atom impact results in the creation of two low-energy Wannier electrons and an ion excited into an autoionizing state. The following autoionization decay exposes the Wannier pair to the influence of PCI resulting in the variation of the shape of the line in the autoionization spectrum. An explicit dependence of the autoionization profile on the wavefunction of the Wannier pair is found. PCI provides an opportunity to study this wavefunction for a wide range of distances.

We have studied dissociative electron attachment (DEA) to condensed by measuring the charge trapping (CT) cross section for submonolayer quantities of on Kr, and by monitoring the electron-stimulated desorption (ESD) of and metastable from and doped Kr and films. Several new channels for DEA are revealed. The largest CT cross section, of approximately , is observed over the incident energy range 0.15 - 1.5 eV and is attributed to DEA, although the possibility that is also stabilized at the lowest energies cannot be excluded. The magnitude of the CT cross section represents an enhancement of more than a factor of 35 relative to the peak gas phase DEA cross section at 2.3 eV. This increase can be attributed to the interaction of the anion state with its polarizable environment. Additional anion states, at , , and possibly , contribute to the DEA yield of . Of these, the 9 and 15.9 eV resonances have no experimentally observed analogues in the gas phase. The charge and energy transfer between the 9.0 eV feature and the state of multilayer Kr films indicates a Rydberg character for this state.

Electron-impact excitation for is studied using close-coupling R-matrix theory in LS coupling. Both 28-state and 40-state close-coupling approximations are employed and cross sections and effective collision strengths for selected excitation transitions are compared. In addition, ionization rate coefficients for are determined using distorted-wave theory and compared with experiment. Finally, these data, along with experimental and theoretical radiative rates, are entered into a collisional-radiative modelling program - (atomic data and analysis structure) to obtain SXB ratios for the radiative transitions and . These SXB ratios allow one to relate spectroscopic emissivity measurements to impurity influx from a localized source. In the present studies, we modelled the impurity influx when only the ground term contributes to the ionization of and showed that the SXB ratio corresponding to the radiative transition between the doublet terms is less sensitive to electron density and more reliable than the SXB ratio corresponding to the radiative transition between the quartet terms. Additional collisional - radiative modelling studies of impurity influx when the ground and metastable states contribute to the ionization of are also proposed.

The effect of dynamically coupling the motion of the impinging positron with that of the molecular nuclei during the scattering process is examined. At the collision energies below the threshold of positronium formation one finds that the effects are increasing the size of the total integral cross sections but are different at different energies. Comparison with experiments is carried out for the target and shows rather good agreement between calculations and the available measurements. The presence of a threshold peak in the inelastic channel is also discussed in analogy with the case of electron scattering from the same molecule.

We compare Kohn - Sham results (density, cohesive energy, size and effect of charging) of the spherically averaged pseudopotential model with the stabilized jellium model for clusters of sodium and aluminium with less than 20 atoms. We find that the stabilized jellium model, although conceptually and practically simpler, gives better results for the cohesive energy and the elastic stiffness. We use the local density approximation as well as the generalized gradient approximation for the exchange and correlation energies.