Table of contents

A treatment of the heavy particle collision dynamics in a form of molecular orbital coupled channel approach, emerging from the hidden crossings topology of the complex adiabatic eigenenergy surface, is proposed. We show how this can be self-consistently adjusted for application in the nearly adiabatic limit of collision energies. The method is tested for the charge transfer process in He²⁺+H collisions, in a range of 10–400 eV/u collision energies. Excellent agreement of the partial and total cross sections with other accurate theories and experiments is shown, and comparative advantages of the method are discussed.

We show that universal properties of a many-atom quantum system exist at a much higher density, or a much shorter length scale, than those implied by traditional theories for a dilute Bose gas. In particular, a universal equation of state at length scale β₆ = (mC₆/ℏ²)^1/4 (corresponding to the van der Waals interaction) is defined and investigated by combining the concept of effective potential, the constrained variational method and the analytic solution for the van der Waals potential. In one application, we show that a many-atom Bose system with negative scattering length may form a metastable liquid Bose–Einstein condensate (BEC) state with an equilibrium density that is controlled by a scaled scattering length.

The recent development of electrostatic devices which allow us to store keV ion beams has launched several new kinds of investigations. We review the basic ideas behind the development of the electrostatic ion storage ring and the electrostatic ion beam trap techniques. The various experiments performed with atomic and molecular ion beams, ranging from the measurement of lifetimes of metastable atomic states up to biological applications and single component plasma studies are discussed.

We study the dynamics of nonlinear localized excitations ('solitons') in two-dimensional (2D) Bose–Einstein condensates (BECs) with repulsive interactions, loaded into an optical lattice (OL), which is combined with an external parabolic potential. First, we demonstrate analytically that a broad ('loosely bound', LB) soliton state, based on a 2D Bloch function near the edge of the Brillouin zone (BZ), has a negative effective mass (while the mass of a localized state is positive near the BZ centre). The negative-mass soliton cannot be held by the usual trap, but it is safely confined by an inverted parabolic potential (anti-trap). Direct simulations demonstrate that the LB solitons (including those with intrinsic vorticity) are stable and can freely move on top of the OL. The frequency of the elliptic motion of the LB-soliton's centre in the anti-trapping potential is very close to the analytical prediction which treats the solition as a quasi-particle. In addition, the LB soliton of the vortex type features real rotation around its centre. We also find an abrupt transition, which occurs with the increase of the number of atoms, from the negative-mass LB states to tightly bound (TB) solitons. An estimate demonstrates that for the zero-vorticity states, the transition occurs when the number of atoms attains a critical number N_cr ∼ 10³, while for the vortex the transition takes place at N_cr ∼ 5 × 10³ atoms. The positive-mass LB states constructed near the BZ centre (including vortices) can also move freely. The effects predicted for BECs also apply to optical spatial solitons in bulk photonic crystals.

This paper reports an experimental investigation of the electron impact detachment of C⁻₄. We observe structure in the electron impact cross section for detaching a single electron from a C⁻₄ cluster anion, which we attribute to the formation and decay of the C²⁻₄ dianion. The system is energetically unstable and very rapidly decays via double autodetachment. The energy and width of the resonance were determined to be 8.8(5) eV and 1.4(5) eV, respectively, and the resonance lies 1.5(5) eV above the ground state of the neutral system. The experiment was conducted by merging monoenergetic electron and ion beams in the heavy ion storage ring CRYRING. The detachment channel was monitored by detecting neutral C₄ fragments.

In view of recent experimental developments and interest, we evaluate the possibility of measuring the absolute phase of a short laser pulse via the asymmetry in the angular distribution of the electron emission. On the basis of quantitative calculations of the ionization of Cs, we demonstrate that the asymmetry is directly related to the initial phase of the field. Our results show that this approach may turn out to have some experimental advantages.

Protonium formation in molecular collisions, , is theoretically investigated. Within the framework of the adiabatic approximation, the four-body problem can be treated as three-body collisions on a single adiabatic (Born–Oppenheimer) potential energy surface (PES), in the same manner as chemical reaction problems. The adiabatic potential energies of the system are calculated for various configurations. A classical trajectory Monte Carlo calculation is carried out for the collisions on the adiabatic PES. It is found that the dissociative dynamics plays a critical role in protonium formation, and consequently the molecular target is much more effective in protonium formation than the atomic-hydrogen target.

Dielectronic recombination (DR) for He-like Ge³⁰⁺ through both one-electron–one-photon and two-electron–one-photon (TEOP) stabilization of Li-like doubly excited states was studied with the Heidelberg electron beam ion trap. The DR resonance strength from He-like Ge³⁰⁺ 1s²¹S₀ to the Li-like Ge²⁹⁺ specific configuration 1s2s²²S_1/2 was determined to be (2.02 ± 0.2) × 10⁻²⁰ cm² eV and the total KLL DR resonance strength was determined to be (63.7 ± 6.5) × 10⁻²⁰ cm² eV. The experimental results agree well with a theoretical prediction obtained with the configuration interaction Hartree–Fock method.

We have measured the triple differential cross section of the Ar²⁺3p⁴(³P^e) state at 20 and 40 eV excess energy in equal and unequal energy sharing conditions, respectively. The present results and previous data of the He²⁺(¹S^e) state measured in the same conditions have been represented by an exact parametrization of the triple differential cross section given by Malegat et al (1997 J. Phys. B: At. Mol. Opt. Phys.30 251; 2002 J. Phys. B: At. Mol. Opt. Phys.35 5169).

Fe Kα_3,4 satellite spectra are investigated using a Johann-type spectrometer at the BL15XU undulator beam line, SPring-8. The intensity of the Kα_3,4 satellite relative to the Kα₁ emission line is found to increase asymptotically with excitation energy up to 9000 eV, almost saturating at 10 000 eV. The satellite threshold energy is found to be 7882 ± 14 eV. This corresponds to the ionization energy of Fe 1s + 2p*, where * indicates that the value is from the Z + 1 approximation. The appearance of a small peak around the [1s2s] double ionization energy suggests that the satellite intensity with the excitation energy can be increased not only by the formation of the 2p spectator holes, but also by a combination of the [1s2s] resonance and [2s2p] Coster–Kronig transition.

We consider the hydrogen molecular ion H⁺₂ in the presence of a strong homogeneous magnetic field. In this regime, the effective Hamiltonian is almost one dimensional with a potential energy which looks like a sum of two Dirac delta functions. This model is solvable, but not close enough to our exact Hamiltonian for relevant strength of the magnetic field. However, we show that the correct values of the equilibrium distance as well as the binding energy of the ground state of the ion can be obtained when incorporating perturbative corrections up to second order. Finally, we show that He³⁺₂ exists for sufficiently large magnetic fields.

The multipartitioning form of the second-order many-body perturbation theory for state-selective effective Hamiltonians is adapted to stabilization calculations of temporary molecular anionic states. We restrict our attention to the simplest case of a system composed of a closed-shell-like molecule and an electron. Pilot applications to the description of the ²Π_g state of the nitrogen molecular anion and the ²Π state of CO⁻ are reported.

This work is considered as a first step towards solving the problem of evaluating the energy shift due to the finite size of muonic molecular ion ddμ (or dtμ) in a molecular complex (ddμ) dee (or (dtμ) dee). The problem is split into two independent parts, corresponding to the 'small', muonic, and the 'large', electronic, subsystems, by introducing a separable approximation to the exact multipole expansion of the perturbation potential. Then the functions, which are related to the dynamic polarizability of the weakly bound states ddμ₁₁ and dtμ₁₁ of muonic molecular ions, are calculated. That further reduces the problem to calculations with the 'large' electronic molecule only.

Dielectronic recombination (DR) has been studied in highly charged He-like Ti ions using an electron beam ion trap. X-rays emitted from radiative recombination (RR) and DR were observed as the electron beam energy was scanned through the resonances. Differential DR resonant strengths were determined by normalizing the DR x-ray intensity to the RR intensity using theoretical RR cross sections. KLn(2 ⩽ n ⩽ 5) resonant strengths were determined for He-like Ti ions. The differential resonant strengths were calibrated without reference to any theoretical DR calculations while the electron energy scale was derived with reference to the well-known energy for ionization of the He-like and H-like ions from the ground state. Calibration in this way facilitates a more exacting comparison between theory and experiment than has been reported previously. To facilitate this comparison, total and differential theoretical resonance strengths were calculated. These calculations were found to be in good agreement with the measured results.

We study the dynamics of a BEC with a singly quantized vortex, placed in the combined potential of a 1D (2D) optical lattice and an axi-symmetric harmonic trap. A time-dependent variational Lagrangian analysis shows that an optical lattice helps to stabilize the vortex which in the absence of the optical lattice is unstable. We find that the normal modes are stable only if the depth of the optical potential is more than a certain critical value. This critical value of the optical potential depends on the 2D interaction parameter. In general, the higher the interaction parameter, the lower the value of the optical potential required to stabilize the vortex. The BEC with the singly quantized vortex is found to be relatively more unstable in a 2D optical lattice compared to a 1D optical lattice.

A phase operator formulation for a recent model of interacting one-dimensional fermions in a harmonic trap is developed. The resulting theory is similar to the corresponding approach for the Luttinger model with open boundary conditions (OBC). However, in place of the spatial coordinate z, a dimensionless variable u defined on the unit circle appears as argument of the phase fields and u is nonlinearly related to z. Furthermore, form factors appear which reflect the harmonic trap geometry. The theory is applied to calculate one-particle correlation functions. In a properly defined thermodynamic limit, bulk and boundary critical exponents are calculated for the static two-point correlation function and the dynamic local correlation function. The local spectral density is also considered. The critical exponents found are in agreement with those known for OBC with the exception of the boundary scaling exponent Δ_⊥.

Ion–atom collisions with active projectile and target electrons are considered in an approach which combines mean-field models for both types of electrons. A previous calculation is improved by taking into account the nonorthogonality of the propagated orbitals. Results for net recoil ion and free electron production in He⁺–Ne and He⁺–Ar collisions are shown to be in good agreement with experiments.

The atomically oriented valence-universal coupled-cluster (VU-CC/R) method in the intermediate Hamiltonian formulation is used to calculate excitation energies for the beryllium and magnesium atoms. Having the basic VU-CC/R scheme which includes one- and two-particle cluster operators (VU-CCSD/R), the effect of approximate inclusion of the three-body terms in the cluster operator is investigated. The evaluation is based on the perturbative analysis of equations for the three-body part of the cluster operator at one- and two-valence levels. In this way, an explicit consideration of the three-body terms is avoided since they are expressed as functions of the two-body clusters. Our results show that the effect of the three-body clusters seems rather small for the systems under consideration which suggests that discrepancies between calculated and experimental values cannot be exclusively attributed to the truncated character of the cluster operator in the VU-CCSD/R calculation.

A theoretical model to calculate the photoion yields registered in coincidence with fixed-energy Auger electrons is developed. The intermediate-coupling approximation is used to calculate the term structure of the two-hole states reached by Auger transitions, and the branching ratios of their further Auger, Coster–Kronig and super Coster–Kronig decays into the three-hole states. The remaining parts of the cascading decay de-excitation trees are simulated in configuration-average approximation for branching ratios and transition energies. Our calculation allowed us to explain the recent M₄₅NN Auger-electron–photoion coincidence experiment upon M₄₅ photoionization of Xe.

We investigate the role of dynamic polarization of the target electrons in the process of recombination of electrons with multicharged ions (polarizational recombination). Numerical calculations carried out for a number of Ni- and Ne-like ions demonstrate that the inclusion of polarizational recombination leads to a noticeable increase (up to 30%) in the cross sections for incident electron energies outside the regions of dielectronic resonances. We also present a critical analysis of theoretical approaches used by other authors to describe the phenomenon of polarizational recombination.