Table of contents

Accurate values for the dipole polarizability of the cyclic form of ozone have been obtained from finite-field many-body perturbation theory and coupled-cluster calculations. Our best effort yields near-Hartree - Fock values of 16.09 and for the mean value and the anisotropy of the dipole polarizability. Electron correlation increases by only a few per cent but has a stronger effect on . Our CCSD(T) values, obtained with a [9s6p5d1f] basis set, are and . Thus, the cyclic form is less polarizable than the open one which is characterized by a mean polarizability of (Maroulis G 1994 J. Chem. Phys. 101 4949).

We present the results of quantum mechanical calculations of the rate coefficients for vibrational relaxation of in H in the temperature range . The results were obtained using two recent and independent calculations of the H - potential, for comparison purposes. Although reactive scattering is excluded from the present study, the results of quasi-classical trajectory calculations which include this process are used to estimate its contribution. The total rate coefficient which is thus obtained is found to be an order of magnitude smaller than that measured by Heidner and Kasper, but it is two orders of magnitude larger than the corresponding values for vibrational relaxation in He or . The need for fresh experimental study is emphasized.

Differential cross sections, integrated cross sections and ionization cross sections for electron scattering on the metastable level of helium are calculated at intermediate energies and compared with experimental measurements and other theoretical calculations. The method used is the coupled-channels optical method with an ab initio complex polarization potential.

Using a transversely polarized electron beam of 300 keV, an (e,2e) experiment has been performed to measure the spin up - down asymmetry in the electron-impact ionization of the K-shells of copper, silver and gold. We found distinct spin asymmetries in the recoil region increasing with the nuclear charge of the target. This is in good agreement with calculations in relativistic distorted-wave Born approximation.

The first extended basis set configuration interaction and coupled cluster calculations have been performed on the lowest excited state of CP. A wide variety of molecular properties are reported, including: (i) spectroscopic constants; (ii) vibrational energies and vibrational excitation energies; (iii) - vibrational transition energies corresponding to several vibrational bands and related Franck-Condon factors; (iv) pure rotational transitions for several values; (v) one-electron properties; (vi) vibrational electric dipole moments and (vii) vibrational and rovibrational lifetimes. For several of the spectroscopic properties it was possible to estimate the complete basis set limit and to include limited core/valence correlation recovery. In general, good agreement was obtained with the limited amount of experimental data that was available. Whenever possible, comparison is made to the corresponding ground state properties and to ground and excited states of closely related diatomics. Finally, the accuracy of the present results are discussed.

Static and dynamic scalar and tensor dipole polarizabilities at real frequencies have been calculated for the two first excited states and of Be using the time-dependent gauge-invariant method (TDGI). The results are compared with the previous accurate theoretical data obtained by Themelis and Nicolaides at the static level. The dynamic results proposed here are new and complete our results published previously concerning the and states. In all cases dynamic components are calculated for dipole polarizability up to the first resonances ( and ) and ( and ) for the singlet and the triplet states, respectively.

The nondegenerate bimodal multiquanta Jaynes-Cummings model (JCM) governed by the Milburn equation is studied. An exact solution of this equation is obtained and applied to investigate the influence of the intrinsic decoherence on nonclassical effects (population inversion, oscillations of the number distribution, squeezing of the field modes), for the resonant and the off-resonant cases.

For the 53 neutral atoms He through Xe in their ground states, the electron repulsion energies between an electron in a subshell nl and another electron in a subshell are studied within the Hartree-Fock framework, where u is the relative (intracule) distance between two electrons, and n and l are the principal and azimuthal quantum numbers of an atomic subshell, respectively. Analysis of a total of 1700 subshell pairs shows that the electron repulsion energy has an empirical but very accurate linear correlation with the smaller of the average reciprocal electron-nucleus distances and of the two relevant subshells. The correlation coefficients are not smaller than 0.999 for all the 66 different combinations of two subshells appearing in the 53 atoms except for two cases. The subshell electron repulsion energy also satisfies a linear relation , where R is the centre-of-mass (extracule) radius of a pair of electrons in subshells nl and , and where the equality with holds exactly when .

We have observed X-ray spectra for 20-2720 keV Ar ions in charge states from 4 through 17 impacting on an surface at from normal incidence. Besides x-rays from the K-shell filling in the case of , we observe characteristic silicon K-shell radiation. The intensity of this radiation is analysed in terms of x-ray fluorescence and vacancy transfer in close atomic collisions.

A simple derivation of Lamb shift in the two-electron helium atom, in the spirit of nonrelativistic quantum electrodynamics, is presented. Moreover, a complete expression for the leading recoil correction is derived for the first time.

Absolute photoabsorption cross sections of strontium have been measured in the energy range extending from the threshold up to above the 6s threshold. The synchrotron radiation source of the Synchrotron Radiation Research Center at Hsin-Chu was used as the background continuum. Strontium vapour was confined in a heatpipe oven. The absolute column density was determined by simultaneously measuring the temperature distribution profiles and the total pressure in the heatpipe. Absolute cross sections were determined using the Beer-Lambert law. The observed spectrum was analysed using a combination of a recent extension of the jj-coupled eigenchannel R-matrix adapted to handle highly correlated levels and the phase-shifted multichannel quantum defect theory. The main features of the observed spectrum, dominated by the presence of many window-type resonances, are well reproduced and the structures are identified. The observed absorption windows result from the fact that only continua are directly excited from the ground state.

We have measured absolute triple differential cross sections for photo-double ionization of helium at 20 eV excess. The measurement covers the full ranges of energy sharing and emission angles of the two photoelectrons. We compare our data for selected geometries with the convergent close-coupling (CCC) calculations as well as 2SC calculations by Pont and Shakeshaft and 3C calculations by Maulbetsch and Briggs. In terms of the absolute magnitude and the trend in the shapes of the triple differential cross section for different geometries we find good agreement of the CCC and published 2SC calculations with our measurement, though differences with respect to the observed shape of individual patterns still exist.

Angle-resolved photoelectron spectroscopy measurements on the molecule are reported, from which -parameters and vibrational branching ratios have been calculated. The measurements were made with good optical resolution in the wavelength region 670-740Å, where several series converge to the state of . The application of the measurements to identifying resonant structure is discussed, and evidence presented for a new series converging to the b state.

The metastable atoms produced by the photodissociation of are detected by observing the enhanced fluorescence of the transition - in the buffer gas xenon. The photodissociation experiments are carried out under conditions of low-pressure (about 100 mtorr) in high-pressure Xe (20-200 torr). The fluorescence spectrum of ) in the wavelength region 510-560 nm is measured.

A strong production of is found at wavelengths between 120 and 140 nm in the state, and a small production observed in the range 105-120 nm. Both spectra seem continuous. The Rydberg states in this wavelength region produce very little O(1S).

The state-resolved isotope effect on the cross sections of 2p atom formation via precursor doubly excited states of and is obtained at 80 eV incident electron energy and scattering angle by means of coincident electron-energy-loss spectroscopy as well as theoretical fits based on the reflection approximation and the survival probability. It turns out that the degree of the isotope effect depends strongly on the precursor doubly excited states and hence is a significant character of them. The origin of this dependence is discussed.

Total cross-sections are reported for the scattering of electrons from ozone and chlorine dioxide (OClO) for energies in the range of 9 meV to 10 eV. The measurements were made in transmission experiments using synchrotron radiation photoionization apparatus with an energy resolution in the incident electron beam of (FWHM). The absolute accuracy of the cross-sections is limited both by experimental difficulties with respect to strong rotationally inelastic forward scattering, due to the dipolar nature of the target molecules, and by the composition of the target gases, which may depart significantly from pure or OClO.

Very marked structure peaking at 50-60 meV in the spectrum of OClO, and a weak feature at a similar energy in , may represent dissociative attachment. With respect to rotationally inelastic scattering, for , we find that the first Born pure dipole approximation is adequate down to energies of 50-60 meV but fails at lower energies, very markedly overestimating scattering cross-sections between 10 and 50 meV. In OClO, the Born approximation fails seriously, even at energies as high as 1-1.5 eV.

The emission spectrum of a pair of effective two-level atoms interacting with two modes of the radiation field with different coupling constants through a multiphoton Raman process is studied. A general expression for the emission spectrum with two modes of the field being in arbitrary states is presented. Our results show that when two modes of the field are in arbitrary number states, the spectrum is always symmetric about the resonant frequency , although the Hamiltonian of the system is asymmetric which is induced by the two different atom-field coupling constants. This property is analysed with an analytic method.

A self-consistent model to simulate the dynamics of charge fluctuations in collisionless fermion gas is described, where the collective aspect of interaction in many-particle charge distributions is taken into consideration. As an application we investigate the dynamics of the degenerate electron gas of a thin Cu metal film, subject to an intense and ultra-short UV laser pulse in resonance with the electron plasma frequency of the system. Results of simulation show that a collective excitation of electrons by resonance absorption leads to the formation of plasma waves in the metal film. The process is accompanied by the appearance of a third harmonic in the photon emission spectrum.

The photoionization of atomic bismuth in the complex autoionization region above the first ionization threshold is studied using spin-resolved photoelectron spectroscopy and Hartree-Fock calculations with relativistic extensions. In spin- and angle-resolved measurements with circularly polarized synchrotron radiation the relative photoelectron intensity and the polarization parameters A and are determined for the strongest resonances. In calculations taking more than 30 different configurations into account all five dynamical photoionization parameters are determined. The agreement with the experimental data is fairly good. Combining calculated and experimental results for the intensity spectrum and the polarization parameter A as well as earlier absorption data, assignments of the first autoionization resonances above the threshold are obtained leading partially to a revision of previous results.

The spin depolarization of the positive muon during slowing down in He, Ne and Ar has been calculated as a function of gas pressure and longitudinal magnetic field strength. The calculation is based on the cross sections for the atomic processes contributing to the slowing down of the positive muon and muonium , obtained from the corresponding cross sections for the proton and hydrogen by simple scaling schemes. The depolarization mechanism taking place in the subpicosecond time regime is discussed in the context of recent experiments to determine the muon decay parameters precisely and accurately in the search for right-handed neutrinos. It has been shown that the polarization loss in He is 1% at and 1 atm pressure, an amount which is unacceptably large for accurate (100 ppm or better) measurements of the muon decay parameters. It is also pointed out that at this level of accuracy a strong longitudinal magnetic field is a much less effective means of quenching the muon spin depolarization mechanism than previously thought. Effects of the electron spin polarization induced by a strong longitudinal magnetic field are also discussed.