Joakim Sandström

Photo-double detachment from the F− ion

The correlated process of photodetaching two electrons from the F − ion following the absorption of a single photon has been investigated over an energy range 20–62 eV. In the experiment, a beam of photons from the Advanced Light Source was collinearly merged with a counter-propagating beam of F − ions from a sputter ion source. The F + ions produced in the interaction region were detected, and the normalized signal was used to monitor the relative cross section for the double-detachment reaction. An absolute scale for the cross section was established by measuring the spatial overlap of the two beams and by determining the efficiency for collection and detection of the F + ions. The measured cross section is compared with R-matrix and random phase approximation calculations. These calculations show that the Auger decay of the 2s2p 6 core-excited state of the F atom plays a minor role in the production of F + ions and that double detachment is likely to be dominated by simultaneous correlated ejection of two valence electrons at energies well above threshold.

Observation of an excited C2−4 ion

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.