X-ray photoelectron spectroscopy (XPS) and KLL Auger spectra of aqueous KCl solution were measured for the K + and Cledges. While the XPS spectra of potassium and chloride have similar structures, both exhibiting only weak satellite structures near the main line, the Auger spectra of these isoelectronic ions differ dramatically. A very strong satellite peak was found in the K + KLL Auger spectrum at the low kinetic energy side of the 1 D state. Using equivalent core models and ab initio calculations this spectral structure was assigned to electron transfer processes from solvent water molecules to the solvated K + cation. Contrary to the potassium case, no extra peak was found in the KLL Auger spectrum of solvated Cl -indicating on a strong dependence of the underlying processes on ionic charge. The observed charge transfer processes are suggested to play an important role in charge redistribution following single and multiple core-hole creation in atomic and molecular systems placed into an environment.Charge transfer (CT) processes and related phenomena are topics of wide relevance in chemistry, physics and biology. They are responsible for numerous important transformations in living organisms and are involved in fundamental steps describing, e.g., the photosynthesis [1] and respiration [2] mechanisms. The creation of a charge (or hole) in a DNA chain, by oxidation or photoionization processes, is quickly followed by its migration along portions of the molecular backbone leading to possible bonds breaking and irreversible damages [3]. Naturally, the use of such very fast elemental processes for technological purposes has attracted an extraordinary large amount of scientists whose research programs -both theoretical and experimental -focus on energy conversion based for instance on photovoltaic or optoelectronic devices [see e.g. ref. [4]].CT may accompany core-hole creation in atoms and molecules which have neighbors, and the corresponding spectral signatures are manifested in XPS spectra as lowenergy CT satellites. Particularly strong CT screening satellites were found in XPS spectra of weak chemisorption systems [5,6], in crystals [7,8], in weakly bound atomic [9] and microsolvated [10][11][12] clusters. As shown in the latter studies, the energy positions and intensities of CT satellites are sensitive to cluster geometries. Furthermore, the type and number of neighbors have strong effects on CT states [13]. CT processes from core-excited metal ions to solvent molecules may quench radiative relaxation processes as observed in fluorescence-yield spectra [14].For elements from the first rows of the periodic table, electronic Auger decay is the main relaxation channel of core-hole states. Core-hole lifetime ranging usually in the femtosecond and sub-femtosecond timescales may serve as an internal reference clock. Using this reference and the relative intensities of spectral peaks, the core-hole clock method allows one to determine timescales of various processes competing to Auger decay, in particular ...

Understanding the mechanisms of X-ray radiation damage in biological systems is of prime interest in medicine (radioprotection, X-ray therapy…). The first step, at the atomic or molecular level, is often...