Licentiate Thesis: Single photon multiple ionization of atoms and molecules studied by coincidence spectroscopy

by Per Linusson (SU Fysikum)

Tuesday 19 Apr 2011, 14:00 → 16:00 Europe/Stockholm

FB42

This thesis concerns multiple ionization of atoms and small molecules induced by the absorption of a single photon. In the experimental study of such processes the coincident detection of all emitted electrons is of great advantage. An electron Time-Of-Flight magnetic bottle spectrometer capable of this has been used for such studies. The method of Coincidence Time-of-Flight spectroscopy and the actual experimental setup used is presented in some detail. Included in the thesis are new experimental and theoretical results on molecular double core holes (DCHs) and doubly ionized atomic cadmium. Molecular DCHs are of considerable interest, as their chemical shifts are predicted to be more sensitive than their single core hole counterparts. However, only very recently new instrumental developments have made it possible to study them experimentally. Using CH4 and NH3 as examples, we show that single-site DCHs can be studied using synchrotron light and a sensitive coincidence technique such as ours. The chemical shifts of S2$p$ core holes are investigated for the molecules CS2, H2S and SO2 and found to be strongly influenced by orbital relaxation. In the study devoted to cadmium we find that the dicationic states are formed mainly by indirect processes. The ionization pathways, some of which show strong channel sensitivity, are investigated in some detail.