Gas-phase spectroscopy

Relativistic and Interchannel Effects in Atomic Photoionization
(Daniele Toffoli and Pietro Decleva)

Unexpected interchannel coupling effects in Xe 3d photoionization (A. Kivimaki et al, PRA 2000, M. Amusia et al., PRL 2002, D. Toffoli et al., JPB 2002) stimulated intense research in the neighbouring Cs and Ba atoms (e.g. H. Farrokhpour et al. JPB 2006, R. Richter et al., PRL 2007). A joint experimental and theoretical study of the effect on Ba was performed at Elettra. Two sharp 3d resonances are observed in photoabsorption (left panel), but only one in photoemission: the decay of the 3d 3/2 ->4f excitation into the 3d 5/2 channel, while the 3d 3/2 channel is completely flat (right panel, 3d 5/2 blue, 3d 3/2 red), as both excitations fall below that threshold. A relativistic TDDFT calculation gives excellent reproduction of the effect. A further theoretical study on the decay of the two resonances in the lower lying channels has been completed (D. Toffoli and P. Decleva, in preparation)

In collaboration with:

  • ELETTRA - GasPhase

Non Dipole Effects in Molecular Photoemission
(Daniele Toffoli and Pietro Decleva)

First results on N2 N1s photoionization by Lindle et al. stirred considerable interest as they detected a large resonant effect close to threshold, which was confirmed by a theoretical calculation (blue curve). More recently new experiments and calculations(A. Yagishita et al. 2006 black, Toffoli and Decleva 2006, Avaldi et al., in progress, red) show a much reduced effect, in good mutual agreement. The experiment proves very tricky, as shown by the persistent disagreement in the valence shell (right figure, left data by Lindle et al.PRL 2006, red dots Avaldi et al., curves: present calculations). We hope to be able to get stable results at Elettra. The theoretical approach gas been extended to trat larger systems: SF6, JCP, in press; C60 in preparation.

In collaboration with:

  • ELETTRA - GasPhase