Auger decay in double core ionized molecules

Abstract

X-ray free electron lasers allow to create and probe double core holes in molecules via successive ionization in considerable amount. The properties of these double core ionized states are in particular relevant for the radiation damage in X-ray coherent diffractive imaging (CDI) experiments with single molecules. In this thesis the Auger decay of double core ionized states in small molecules is investigated via quantum chemical ab-initio methods. To model the emitted Auger electrons at continuous energy levels the single center method is used, in which the electronic wave function is described on a radial grid using spherical harmonics. As shown for the example of a water molecule, the proton dynamics induced by the double core ionization is reflected in the Auger spectrum by marked tails on the high-energy part of each spectral peak. The life time of double core holes in molecules is significantly reduced compared to that of single core holes due to the core hole induced screening effects of the valence electrons. This mechanism is explained by a simple model from which a relation for the decay rate and valence electron population is derived. Possible consequences of these results for X-ray diffraction experiments are: First, even for pulses shorter than 10fs the diffraction patterns is biased by the core hole induced rearrangement of the electronic valence structure. Second, the overall ionization rate is enhanced because of the faster refilling of double core holes.