Angular correlations in radiative cascades following resonant electron capture by highly charged ions

We investigate the angular correlations between the photons emitted in the dielectronic recombination (DR) of initially hydrogenlike heavy ions. The theoretical analysis is performed based on a density-matrix approach and Dirac's relativistic theory. Special emphasis has been placed upon the effects of the higher-order, nondipole terms in the expansion of the electron-photon interaction. To illustrate these effects, we present and discuss detailed calculations for K-LL DR of initially hydrogenlike xenon, gold, and uranium. These computations show that the angular correlations are significantly affected by interference between the leading electric-dipole (E1) and the magnetic-quadrupole (M2) transitions.

Photon collisions with atoms and ions within an intermediate-energy R-matrix framework

Recent experimental advances in light technology necessitate the availability of sophisticated theoretical models which can incorporate an accurate treatment of double-electron continua. We describe here a new intermediate-energy R-matrix approach to photoionisation and photo-double-ionisation and illustrate its feasibilty by application to photoionisation and photo-double-ionisation of He, and photodetachment and photo-double-detachment of H^-. Results are shown to be in excellent agreement with previous theoretical and experimental studies. This work is a key step in the development of a multipurpose R-matrix code for multiple-electron ejection. © 2012 American Physical Society

Fluorescence yields for 3lnl′ Rydberg series in ions belonging to the He isoelectronic sequence

Fluorescence yields are reported for 3lnl' Rydberg series members in He-like ions of N, O and Ne. Results are presented for singlet series members with n values between 3 and 9, i.e. up to the region of overlap with the states belonging to the 4l4l' manifold in these atoms. This data is required, for example, for the interpretation of charge-exchange experiments involving bare N, O and Ne nuclei. Fluorescence yields, averaged over all 3lnl' singlet states, larger than 50% are obtained from about n = 7.

R-matrix Floquet theory of multiphoton processes:VI. The negative halide ions

The R-matrix Floquet approach is applied to study the negative F and Cl ions in a light field. Detachment rates are obtained for detachment processes involving up to three photons. The results obtained in the present approach are compared to other experimental and theoretical results. For two- and three-photon processes reasonable agreement with other calculations has been found, while for two-photon detachment the results agree with the experimental cross sections. The three-photon results are in less good agreement with experiment although the larger error bars make accurate comparisons more difficult. The changes in the detachment behaviour for these ions are compared to each other as well as to the detachment behaviour of H.

Recoil-induced electronic excitation and ionization in one-and two-electron ions

The electronic redistribution of an ion or atom induced by a sudden recoil of the nucleus occurring during the emission or capture of a neutral particle is theoretically investigated. For one-electron systems, analytical expressions are derived for the electronic transition probabilities to bound and continuum states. The quality of a B-spline basis set approach is evaluated from a detailed comparison with the analytical results. This numerical approach is then used Io study the dynamics of two-electron systems (neutral He and Ne ) using correlated wavefunctions for both the target and daughter ions. The total transition probabilities to discrete states, autoionizing states and direct single- and double-ionization probabilities are calculated from the pseudospectra. Sum rules for transition probabilities involving an initial bound state and a complete final series are discussed.

Structure and interactions of ultracold Yb ions and Rb atoms

In order to study ultracold charge-transfer processes in hybrid atom-ion traps, we have mapped out the potential-energy curves and molecular parameters for several low-lying states of the Rb, Yb+ system. We employ both a multireference configuration interaction and a full configuration interaction (FCI) approach. Turning points, crossing points, potential minima, and spectroscopic molecular constants are obtained for the lowest five molecular states. Long-range parameters, including the dispersion coefficients, are estimated from our ab initio data. The separated-atom ionization potentials and atomic polarizability of the ytterbium atom (ad=128.4 atomic units) are in good agreement with experiment and previous calculations. We present some dynamical calculations for (adiabatic) scattering lengths for the two lowest (Yb, Rb+) channels that were carried out in our work. However, we find that the pseudopotential approximation is rather limited in validity and only applies to nK temperatures. The adiabatic scattering lengths for both the triplet and singlet channels indicate that both are large and negative in the FCI approximation.