Table of contents

Simple analytic expressions have been obtained for the electron energy spectra of atoms and atomic ions undergoing direct tunnelling ionization by linearly polarized laser radiation. The new results are analytic expressions for the high-energy part of the energy spectrum for when the electron kinetic energy is of the order of or greater than the ponderomotive electron energy. The contribution from direct tunnelling ionization in the hot part of the energy spectrum can be comparable with the contribution from the tunnelling ionization occurring in the rescattering processes. The high-energy part of the energy spectrum is independent of the ionization potential of the atom considered.

Non-dipole 3p → 2p x-ray emission was observed for the first time after resonant and non-resonant production of a 2p core hole in solid cobalt, nickel, copper and copper oxide. In all the materials studied, this emission follows a resonant Raman scattering behaviour. Its emission energy and its intensity relative to the 3s → 2p_3/2 transition are compared with a free ion Hartree–Fock calculation. The emission energy for the non-dipole transition is in good agreement with the calculations, but the measured intensity is about one order of magnitude larger than the calculations predict. A compression or distortion of the 3p orbital in the solid is suggested as the cause for the intensity enhancement.

Many new resonances in neon have been discovered by virtue of their LS-forbidden mirroring partial cross section profiles. In particular, all six of the previously undetected 2s²2p⁴(³P)3s(^[2,4]P)3p(³[S, P, D] ₁) resonances have been observed. These results confirm our earlier prediction (Canton-Rogan et al 2000 Phys. Rev. Lett.85 3113) that mirroring triplet resonances are observable in partial cross sections where continuum spin–orbit effects exist, and suggest that future experimental studies of other atoms will also reveal new resonances.

We present experimental data on charge transfer from coherent elliptic states of Rydberg atoms, which are oriented relative to the impact velocity vector of monoenergetic, singly charged ions. The data cover a broad range of scaled velocities around unity, selected angles of approach over the whole sphere, all eccentricities from zero to one and principal quantum numbers ranging from n = 20 to 35. The cross sections show good qualitative agreement with classical trajectory Monte Carlo calculations, but clear deviations are also observed.

Energy spectra of the ground configuration and the first four excited configurations of fluorine-like potassium K XI have been calculated using the configuration interaction method. The wavelengths and transition probabilities of one-electron and two-electron transitions are obtained ab initio. The probabilities of one-electron transitions 2s²2p⁴3p–2s²2p⁴3s and two-electron transitions 2s²2p⁴3p–2s2p⁶ for determination of lifetimes of the levels of configuration 2s²2p⁴3p are used. The calculated results are compared with the recent experimental data and other theoretical results.

A simple method for the description of the coherent electron emission from two H atoms of the H₂ molecule induced by particle impact is suggested. The method is based on a formalism that separates the cross section for the electron emission into an atomic part describing the independent emission from the two H atoms, and a factor giving an account of the interference caused by the coherent emission from the two centres. This separability allows the use of a classical ionization theory to determine the atomic part of the cross section. Calculations applying the classical trajectory Monte Carlo (CTMC) theory have been carried out for 68 MeV amu⁻¹ Kr³³⁺ on H₂ collisions. A reasonable agreement has been found between the CTMC results and the recent experimental data obtained by Stolterfoht et al.

We present an extension of the discrete momentum representation method for a vibrationally inelastic scattering of electrons by polyatomic molecules. We have developed a fully ab initio procedure, based on two-channel Lippmann–Schwinger equations expanded in the momentum space. Static and exchange contributions are obtained explicitly. Results are presented for H₂ and H₂O molecules.

The field ionization and Coulomb explosion of diatomic carbon monoxide interacting with intense femtosecond laser pulses was systematically investigated by using a time-of-flight mass spectrometer. The kinetic energy release (KER) in a Coulomb explosion causes the atomic ions to exhibit a double-peak structure. The values of KER calculated using a two-step model were found to agree well with the measured ones. The distributions of atomic ions are highly anisotropic, having a maximum along the laser polarization axis and a minimum perpendicular to it. In contrast to the atomic ions, the parent ion CO⁺ exhibits a strong isotropic angular distribution. Suppression of ionization was observed for circularly polarized pulses, indicating that the dynamic alignment is responsible for the observed anisotropic angular distribution of the atomic ions.

The hyperfine structures of ^7,9Be⁻  2s2p^{2  4}P _1/2,3/2,5/2 are investigated theoretically using the multiconfiguration Hartree–Fock and configuration interaction methods. The effects of the hyperfine mixing between the fine-structure J-levels are discussed. The feasibility of some atomic spectroscopy experiments, allowing determination of the ⁷Be quadrupole moment from the observed hyperfine structure of the ⁷Be⁻ negative ion and from the present electronic parameters, is investigated. The Be 2s2p ³P^o electron affinity is monitored as a function of the orbital and configuration spaces to assess the reliability of the wavefunctions of the neutral atom and the negative ion. The theoretical value nicely converges towards the most recent theoretical and experimental results.

Substantially larger calculations than previously possible are performed to examine how the convergent close-coupling method converges in the case of electron-impact ionization of atomic hydrogen. By studying the case of 27.2 eV incident electron energy, convergence and comparison with experiment is able to be considered together for both symmetric and asymmetric energy sharing. We find that, with Laguerre basis parameter choices of N_l = N₀ − l and λ_l = λ, excellent agreement with experiment is obtained for all kinematical conditions and geometries considered.

The convergent close-coupling (CCC) method is applied to the calculation of electron–helium ionization doubly differential cross sections (DDCSs) at low to intermediate incident energies. We re-examine the CCC calculations and measurements of Röder et al (1997 J. Phys. B: At. Mol. Opt. Phys.30 1309–22) by making allowance for the step-function behaviour of the underlying CCC-calculated amplitudes. As done previously, the experimental DDCS were normalized at energies below 100 eV using the 100 eV CCC calculation to determine analyser properties at several secondary energies. In addition, substantially larger calculations are presented, to check the convergence. The agreement between the experiment and the calculations as a whole is much improved on the situation reported earlier.

The Z-dependence of external bremsstrahlung (EB) produced by beta particles of ¹⁴⁷Pm and ³²P beta emitters in Al, Cu, Sn, and Pb targets has been studied, as a function of photon energy, on the basis of the theoretical and experimental EB spectral distributions. The present results show that the values of the Z-dependence index, obtained both from Elwert-corrected Bethe–Heitler and Tseng and Pratt theories and from experiments, are not constant. It is found that the index n increases with increasing photon energy.

Dissociative photoionization of N₂ is studied with synchrotron radiation in the 24–32 eV photon energy range. Branching ratios between the different dissociation limits are measured from coincidence time of flight ion spectra threshold photoelectron–photoion coincidence recorded for state-selected N₂⁺ parent ions. In this energy range, N₂⁺ molecular ions are observed to dissociate only towards the three lowest dissociation limits. Dissociations towards the second and third ones, which correspond to the formation of N⁺(¹D) and N(²D) metastable states, respectively, occur right from their thermochemical onsets. From the second dissociation limit energy up to the third one, the N⁺(¹D) + N(⁴S)/N⁺(³P) + N(⁴S) branching ratio is almost constant and equal to 0.6:0.4, except at the energy of the C ² Σ _u⁺ (v = 12) state, where this branching ratio is found to be equal to 0.5:0.5. From the third dissociation limit onset, N₂⁺ ions fragment only towards this limit. Possible dissociation mechanisms are discussed, involving a spin–orbit coupling between doublet and quartet states of N₂⁺ to produce N⁺(¹D) + N(⁴S) and a direct dissociation to produce N⁺(³P) + N(²D). No dissociation towards the other limits has been observed, in particular to produce the N⁺(¹S), N⁺(⁵S) and N(²P) metastable states.

A numerical and analytical study of the Zitterbewegung of a wavepacket of Volkov wavefunctions is presented. The amplitude of the trembling motion is shown to follow periodic collapses and revivals. This time dependence is explained from two different points of view: first relating the Volkov wavepacket with a Jaynes–Cummings model, and second by direct inspection of the dynamics of the wavepacket. Both explain perfectly the result obtained from the numerical simulations.

Bifurcation analysis is applied to the spontaneous spatial symmetry breaking occurring in the ground state of two-component Bose–Einstein condensates. The cusp catastrophe describing the supercritical pitchfork bifurcation associated with the symmetry breaking is derived via the identification of the local curvature of the Gross–Pitaevskii energy functional. The bifurcation diagram and universal scaling laws for the eigenvalue and energy are obtained from the catastrophe function.

The probabilities of total, radiative and radiationless vacancy transfer from the K shell to the L₁, L₂ and L₃ subshells were determined for the elements Ce, Pr and Nd using L x-ray production cross-sections. L x-rays from targets excited by 59.5 keV incident photons, above the K edges of the elements, were detected with a high-resolution Si(Li) detector. The results measured were compared with theoretical values based on the Hartree–Slater wavefunction. They are found to be in good agreement.

By using time-dependent density functional theory, the vertical excitation energies of the boron monoiodide molecule are calculated. The Vosko–Wilk–Nusair functional with Stoll correction is used as the local density approximation, while the RPBE functional is used as the general gradient approximation for the calculations of vertical excitation energies. The potential energy curves of the ground state, the 12 valence states and the eight Rydberg excited states are plotted. The spectroscopic constants, including the equilibrium internuclear distance, r_e, the harmonic vibrational wavenumber, ω_e, and the relative electronic energy referred to the ground state, T_e, of bound states, are obtained theoretically for the first time. The transition properties of the ¹ Π–X ¹Σ⁺ transition, including the transition dipole moments, the radiative lifetimes and the Franck–Condon factors, are predicted.

The Harris–Nesbet variational method was considered for the calculation of phase shifts of electron collisions with hydrogen-like ions (Li²⁺, Be³⁺, and B⁴⁺). Calculations were carried out for both singlet and triplet scattering. Very accurate results of phase shift of electron collisions with these ionic targets were obtained for the first time for partial waves of L up to six. The phase shifts that we obtained for low partial wave (S, P, and D) scattering were compared with those available in the literature by a few other research groups employing different numerical methods.

A theory of spectral distribution of the rotational molecular time correlation function for a system consisting of a linear molecule active in a given process and an atomic perturber has been developed. Within the framework of the proposed approach the coupling between the rotational and translational degrees of freedom due to anisotropic intermolecular interactions has been considered. In order to analyse the effect of the rotational level mixing and propagation the stationary phase method has been used. The theory has been shaped in such a way that its final formulae would form a fully numerically tractable procedure, capable of producing orientational parts of spectral profiles for collision-induced absorption and scattering processes, which might be used for the interpretation of experimental results. Numerical calculations have been performed for N₂–Ar pairs and the properties of the resulting spectral distributions have been studied, with special attention paid to their dependence on the angular momentum quantum number J.

We propose an approach to treat ionization of light atoms in relativistic collisions with highly charged ions, where the electromagnetic field generated by the ions can be very strong. The approach is based on the observation that, for a collision with a certain momentum transfer, either the relativistic effects, connected with the collision velocity approaching the speed of light, or the higher-order terms in the corresponding Born series in the projectile–target interaction can be of importance for the ionization process. The approach consists of dividing all collisions into those with 'small' and 'large' momentum transfers, which are described by (the first order of) the relativistic Born and the Glauber approximations, respectively. The approach is applied to describe helium single ionization by 1 GeV u⁻¹ U⁹²⁺ projectiles.

We have carried out relativistic distorted wave calculations for the excitation of the 6³P ₁ and 6¹P ₁ states of mercury from the ground ¹S ₀ state by spin-polarized electrons. The ground and excited states are represented by multiconfiguration Dirac–Fock wavefunctions. We have corrected previously published expressions for the generalized Stokes parameters (GSP) and the complete set of independent scattering parameters. Results for GSP, generalized STU parameters and the complete set of independent scattering parameters for incident electrons with an energy of 8 eV are obtained and compared with the available experimental data and theoretical semirelativistic R-matrix and distorted wave Born approximation calculations.

Electron capture from ground state hydrogen atoms by protons is theoretically studied by using a two-state approximation with a continuum distorted wave basis. The total charge transfer cross section for this collision is obtained through the Oppenheimer scaling rule from the analysis of capture in the 1s state. Comparison with experimental values in the energy range 0.1 eV–10 MeV shows that good agreement is obtained for all these energies.

Electron-impact excitation of the 5³P ₁ (12.062 eV) and 5¹P ₁ (12.810 eV) 4d⁹5s²5p autoionizing states of Cd has been experimentally investigated at incident electron energies (E₀) from 15 to 60 eV and scattering angles (θ) up to 40° (at E₀ = 40 eV, θ = 2°–150°). The absolute differential cross sections (DCSs) at E₀ = 40 eV were determined through normalization to the optical oscillator strengths. These DCSs were extrapolated to 0° and 180° and numerically integrated to yield integral, momentum transfer and viscosity cross sections. Energy-loss spectra for Cd were recorded from 11 to 18 eV, and 22 autoionizing states were identified at different impact energies. Electron-impact excitation of the 3d⁹4s²4p autoionizing states was observed in energy-loss spectra of Zn at E₀ = 20, 60, 80 and 100 eV (θ up to 10°). The DCSs for Cd could not be compared with other results, because there are no available data in literature. The autoionizing energy levels and line widths are in good agreement with existing experimental and calculated values.

In December 2002 we announced some changes to Journal of Physics B: Atomic, Molecular and Optical Physics: an extended scope to highlight the wide range of articles published in the journal and a new definition of Letters to the Editor. As always, comments and suggestions are welcome and should be sent to jphysb@iop.org.

Extended scope of J. Phys. B

J. Phys. B covers all aspects of atomic, molecular and optical physics. We publish articles on the study of atoms, ions, molecules, condensates or clusters, from their structure and interactions with particles, photons, fields and surfaces to all aspects of spectroscopy. Quantum optics, non-linear optics, laser physics, astrophysics, plasma physics, chemical physics, optical cooling and trapping and other investigations where the objects of study are the elementary atomic, ionic or molecular properties of processes are also included.

With the introduction of the BEC Matters! portal and IOP Select, J. Phys. B, one of the major contributors, offers authors of articles in this research area wider visibility and more flexible publication with the opportunity to display multimedia attachments or web links to key groups and results. The recent papers listed below reflect the wide scope of J. Phys. B:

Calculation of cross sections for very low-energy hydrogen-antihydrogen scattering using the Kohn variational method E A G Armour and C W Chamberlain J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 22 (28 November 2002) L489-L494

Imaging the electron transfer reaction of Ne²⁺ with Ar using position-sensitive coincidence spectroscopy Sarah M Harper, Wan-Ping Hu and Stephen D Price J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 21 (14 November 2002) 4409-4423

Ultraviolet-infrared wavelength scalings for strong field induced L-shell emissions from Kr and Xe clusters Alex B Borisov, Xiangyang Song, Fabrizio Frigeni, Yang Dai, Yevgeniya Koshman, W Andreas Schroeder, Jack Davis, Keith Boyer and Charles K Rhodes J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 21 (14 November 2002) L461-L467

A Bose-Einstein condensate in an optical lattice J Hecker Denschlag, J E Simsarian, H Häffner, C McKenzie, A Browaeys, D Cho, K Helmerson, S L Rolston and W D Phillips J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 14 (28 July 2002) 3095-3110

Locality of a class of entangled states I R Senitzky J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 14 (28 July 2002) 3029-3039

Solitons and vortices in ultracold fermionic gases Tomasz Karpiuk, Miroslaw Brewczyk and Kazimierz Rzazewski J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 14 (28 July 2002) L315-L321

Stable islands in chaotic atom-optics billiards, caused by curved trajectories M F Andersen, A Kaplan, N Friedman and N Davidson J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 9 (14 May 2002) 2183-2190

Emission probability and photon statistics of a coherently driven mazer Jin Xiong and Zhi-Ming Zhang J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 9 (14 May 2002) 2159-2172

The Li⁺-H₂ system in a rigid-rotor approximation: potential energy surface and transport coefficients I Røeggen, H R Skullerud, T H Løvaas and D K Dysthe J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 7 (14 April 2002) 1707-1725

The stochastic Gross-Pitaevskii equation C W Gardiner, J R Anglin and T I A Fudge J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 6 (28 March 2002) 1555-1582

Oxygen ion impurity in the TEXTOR tokamak boundary plasma observed and analysed by Zeeman spectroscopy J D Hey, C C Chu, S Brezinsek, Ph Mertens and B Unterberg J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 6 (28 March 2002) 1525-1553

Electron-hexafluoropropene (C₃F₆) scattering at intermediate energies Czeslaw Szmytkowski, Pawel Mozejko and Stanislaw Kwitnewski J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 5 (14 March 2002) 1267-1274

High-resolution investigations of C₂ and CN optical emissions in laser-induced plasmas during graphite ablation S Acquaviva and M L De Giorgi J. Phys. B: At. Mol. Opt. Phys. Vol 35, No 4 (28 February 2002) 795-806

New definition of a Letter to the Editor

A Letter to the Editor should present new results, likely to stimulate further research and be of interest to the wider atomic, molecular and optical physics community. Above all the results should be sufficiently new and important to merit rapid publication as a Letter, which implies accelerated refereeing procedures. This should be made clear either in the body of the Letter, if appropriate, or with a supporting cover letter from the author on submission to the journal.

Letters will have an upper limit of eight journal pages and, as an additional quality check, two referees instead of one will be used to review them. The Board will be asked to make a final publication decision in the event of two conflicting reports.

With these measures in place it is hoped that the important new results will receive the exposure they deserve as a Letter.

If you have any questions or comments on this or anything relating to J. Phys. B please contact Nicola Gulley, Publisher, J. Phys. B (E-mail: jphysb@iop.org).