I. Sánchez

Representation of the electronic continuum of with B-spline basis

We present an integrable method with B-spline basis to describe the electronic continuum of two-electron diatomic molecules. The method is applied to obtain (i) energy positions and widths of the lowest doubly-excited states of the molecule, and (ii) photoionization cross sections of in the fixed-nuclei approximation. Our results are compared with existing theoretical and experimental works. We show the existence of avoided crossings between two series of doubly-excited states, and , converging to the ionization threshold of .

Photoionization of He-like systems below the N=2 threshold

The authors have implemented a recently proposed L2-integrable basis method to study photoionization of He-like systems below the n=2 threshold in the framework of a Fano-Feshbach theory. Non-resonant background cross sections and Fano parameters for the (2, n)1P degrees doubly excited states of He and Li+ up to N=5 are calculated. For n>or=3 an anomalous behaviour of the profile parameter q is found in He, which is the result of the existence of interfering, but nevertheless non-overlapping, resonances in the (2, nb) and (2, nc) series. The behaviour of photoionization parameters as a function of the nuclear charge is also discussed.

Electron angular distribution in above-threshold two-photon detachment of

We present angular-differential above-threshold two-photon detachment rates of below the second ionization threshold. They have been calculated using an close-coupling method with a B-spline basis. We have found that in the non-resonant region the angular distribution of photoelectrons is close to that obtained from a pure D partial wave. This is also the case in the vicinity of the lowest doubly excited state. In contrast, the angular distribution in the vicinity of the doubly excited states is the result of a complicated interference pattern between S and D waves. In the latter case, knowledge of the corresponding phase shifts is essential to interpret the actual results.

Asymmetry parameters in two-photon detachment of below 1 eV

We present theoretical calculations for two-photon detachment rates and asymmetry parameters of for energies below 1 eV. The calculated asymmetry parameters compare very well with values determined in a recent experimental work. This is the first time that this kind of comparison has been made for , which reinforces the predictive value of previous theoretical works on the two-photon detachment of for which experiments are still lacking.

Fluorescence yields for

Fluorescence yields are reported for 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 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 singlet states, larger than 50% are obtained from about n = 7.

3InI'

The systematics of resonance parameters in the photoionization of He-like ions above the N=2 threshold is discussed along the isoelectronic series. We show that a simple Z scaling of the resonance parameters is only achieved for large nuclear charges due to the unexpected cancellation of the Fano interferences near Z=5.