Table of contents

R-matrix calculated photoelectron angular distribution asymmetry parameters, β, for Cl⁺ 3s3p⁵³P^o and 3s²3p³(²D^o)3d ¹P^o final ionic states in photoionization of the ground state of atomic Cl are presented in the photon energy range from threshold to 80 eV. The results, characterized by prominent autoionization structures which are sensitive to multielectron correlations, are compared with those recently measured by Whitfield et al (Whitfield S B, Kehoe K, Krause M O and Caldwell C D 2000 Phys. Rev. Lett.84 4818). Contrary to experiment and previous theoretical calculations, our detailed CIV3 structure calculation (Deb N C, Crothers D S F, Felfli Z and Msezane A Z 2002 J. Phys. B: At. Mol. Opt. Phys. submitted) has identified the lowest ¹P^o level of Cl⁺ as 3s²3p³(²D^o)3d ¹P^o rather than 3s3p⁵¹P^o. The implications and consequences of the measured data for the 3s ¹P^o level are also discussed in the context of our calculated energies for Cl⁺ and β for 3d ¹P^o.

Analytic expressions of some physical quantities for Rydberg transitions, like the first Born cross section for the n → n' transition, are found to contain terminating hypergeometric functions of large arguments which pose certain analytical and numerical problems that are well documented. We describe a simple method based on the use of the Jacobi polynomial to understand analytic properties and deduce an asymptotic expression of a general terminating hypergeometric function. To illustrate the utility, we apply the method to the n → n' Born cross section, for which situation the Tricomi asymptotic method had been used earlier in the literature. It is found that the Jacobi polynomial method gives strikingly good results for n → n' transitions over the entire range of the physical momentum transfer, in contrast to the Tricomi asymptotic method which gives unrealistically large results for large momentum transfers.

The energy curve of the hydrogen–antihydrogen system has been calculated using the Rayleigh–Ritz variational method, with a basis of correlated Gaussian functions. The microHartree accuracy of Born–Oppenheimer energies of this system has been achieved for the first time for short internuclear distances. The new upper bound to the terminal distance of Ps binding by the p– pair has been established to be 0.744 Bohr.

The radiative decay dynamics of an atomic (nuclear) excited state split into two neighbouring sublevels are considered for the case of interaction with a low-frequency electromagnetic field. The conditions of cancellation of the spontaneous emission in this system are analysed beyond the rotating wave approximation.

We study the stability of vortices in trapped single-component Bose–Einstein condensates within self-consistent mean-field theories; in particular, we consider the Hartree–Fock–Bogoliubov–Popov theory and its recently proposed gapless extensions. It is shown that for sufficiently repulsively interacting systems the anomalous negative-energy modes related to vortex instabilities are lifted to positive energies due to partial filling of the vortex core with noncondensed gas. Such behaviour implies that within these theories the vortex states are eventually stable against the transfer of condensate matter to the anomalous core modes. This self-stabilization of vortices, shown to occur under very general circumstances, is contrasted to the predictions of the non-self-consistent Bogoliubov approximation, which is known to exhibit anomalous modes for all vortex configurations and thus implying instability of these states. In addition, the shortcomings of these approximations in describing the properties of vortices are analysed, and the need for a self-consistent theory taking properly into account the coupled dynamics of the condensate and the noncondensate atoms is emphasized.

An equivalence of electronic Coulomb matrix elements to those of contact interactions between longitudinal transition current densities is presented. The use of this can lead to significant simplifications of calculations of energies and wavefunctions in systems where these properties depend on interactions between many electrons. Different applications to excited states and ground states of atoms and molecules are suggested and discussed.

The eigenstate problem of the Jaynes–Cummings model on the basis of a complete Hamiltonian, including the centre-of-mass kinetic energy operator, is considered. The energy spectrum and wavefunctions in the standing-wave (SW) and counterpropagating-wave (CPW) cases are calculated and compared with each other. It is shown that in the CPW case: (i) the atomic momentum distribution is asymmetric; (ii) the concept of quasimomentum is not applicable and instead the problem concerns the ordinary momentum; (iii) atomic and photonic state distributions are self-consistent; and as a consequence (iv) the mean number of photons in counterpropagating travelling waves and mean atomic momentum are matched. Explicit analytic expressions are proposed to describe the transition from counterpropagating quantized waves to a standing wave. It is also shown that, if the recoil energy is taken into account, the Doppleron resonance is split into two branches, one of which diverges to Bragg-like resonance in high-order range.

The density functional theory for molecules (DMol) method based on density functional theory is used to study the structural stability of the neutral and charged icosahedral Ti₁₂X clusters with X = B, C, N, Al, Si, P, V, Cr, Mn, Fe, Co and Ni. Geometry relaxation calculations are carried out to obtain the binding energy (BE) and the electronic structure of the cluster at the ground state. It is found that Ti₁₂Fe²⁻, Ti₁₂Co¹⁻ and Ti₁₂Ni clusters are the most stable structures; they have the lower BEs and are closed-shell systems with large energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital.

The depolarized interaction-induced light scattering spectrum of argon gas at room temperature, over an extended frequency domain with comparable accuracy, and ranging from 0 to 400 cm⁻¹ with high-energy beam results and pressure virial coefficients, has been used to derive the empirical isotropic multiparameter Morse–Morse–Morse-spline–van der Waals interatomic potential. Absolute zeroth, second and fourth moments of the binary spectrum have been measured and compared with theoretical calculations using various models for the interatomic potential. In addition, vibrational energy levels and viscosities calculated for the new potential are compared with experimental ones. The results show that it is the most accurate potential reported to date for this system.

Angle-resolved patterns of the differential cross section for resonance-affected photo double-ionization in neon under the conditions of equal and slightly unequal energies of the ejected electrons are calculated using ab initioN-electron scattering wavefunctions that take into account interference, exchange and correlation effects. Post-collisional interactions are included a posteriori, correcting the direct and resonant amplitudes in the scattering wavefunctions by means of separate correlation factors taken from the literature. The method used for constructing scattering wavefunctions with two electrons in the continuum is described in detail. Comparison between theoretical cross sections convoluted with apparatus functions and available experimental data (Schaphorst S J, Jean A, Schwarzkopft O, Lablanquie P, Andric L, Huetz A, Mazeau J and Schmidt V 1996 J. Phys. B: At. Mol. Opt. Phys.29 1901; Rioual S, Rouvellou B, Avaldi L, Battera G, Camilloni R, Stefani G and Turri G 2000 Phys. Rev. A 61 044702 and Rioual S, Rouvellou B, Avaldi L, Battera G, Camilloni R, Stefani G and Turri G 2001 Phys. Rev. Lett.86 1470) shows close agreement. Resonant, direct and interference contributions to the differential cross sections and geometrical features of the electron emission are analysed in detail.

By shining a tightly focused laser light on a Bose–Einstein condensate (BEC) and moving the centre of the beam along a spiral path one may stir the BEC and create vortices. It is shown that one can induce rotation of the BEC in the direction opposite to the direction of stirring.

A simple empirical formula has been found which factors out the gross target dependence of single ionization cross sections by positron and electron impact. The formula can be used to estimate cross sections for an atom if the cross section maxima for any other two atoms in the same column of the periodic table are known. Further investigation is required to understand the basic physical mechanism underlying the degree of accuracy of such a factorization.

For the first time, quantum chemical and Car–Parinello molecular dynamics simulations of rotation strength dispersion, using restricted Hartree–Fock (RHF) and density functional theory (DFT) approaches, for a biscyanine dye with Schiff base (BDSB) molecule as a model have been performed. We have found that most of the DFT approaches give substantially better agreement with the experimental structural and optical data than the RHF. Contributions of the magnetic-dipole and quadrupole-dipole interactions to the rotation strength spectra were separated. For this reason independent measurements of the rotational strengths (RSs) for the oriented and disordered BDSB molecule were performed. A significant contribution of the anharmonic electron-vibration interaction to the RS was found.

The spontaneous decay rates for the electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1) and magnetic quadrupole (M2) transitions between all of the 1s², 1s2 l and 1s3 l states have been obtained for helium-like calcium and sulfur ions. To assess the accuracy of the calculations, the transition probabilities were calculated using two sets of configuration interaction wavefunctions. One set of wavefunctions was generated using the fully relativistic GRASP code and the other was obtained using CIV3, in which relativistic effects are introduced using the Breit–Pauli approximation. The transition rates, A values, oscillator strengths and line strengths from our two calculations are found to be similar and to compare very well with other recent results for Δn = 1 or 2 transitions. For Δn = 0 transitions the agreement is much less good; this is mainly due to differences in the calculated excitation energies.

The variation of the valence electron wavefunction inside a nucleus induced by a perturbative potential is expressed in simple explicit terms, as the zeroth and first momenta of the potential. As an application we consider the QED vacuum polarization corrections to the parity non-conservation amplitude, caused by the Uehling and Wichmann–Kroll potentials. The Uehling potential is found to give −0.47% for the amplitude of the 6s–7s transition in ¹³³Cs, while the contribution of the Wichmann–Kroll potential is proved to be negligible.

Electron-impact dissociative ionization of the CH₃F molecule has been studied in a double-focusing time-of-flight mass spectrometer. The absolute partial ionization cross sections of the nascent ions, namely CH₃F⁺, CH₂F⁺, CHF⁺, CF⁺, HF⁺, F⁺, CH₃⁺, CH₂⁺, CH⁺, C⁺, H₂⁺ and H⁺, have been measured for impact electron energies up to 100 eV and the total ionization cross section was computed by adding up the partial ionization cross sections of the set of ejected ions. Kinetic energy distributions and appearance potentials of the nascent ions were also characterized and further compared with the thermodynamic appearance energies in order to provide the identification of the dissociative ionization channels. A discussion of the correlation between the channel appearance potentials and the precursor bond character and molecular orbital energies is also presented.