Efficient Pathway to Neutralization of Multiply Charged Ions Produced in Auger Processes

Abstract

After core ionization of an atom or molecule by an x-ray photon, multiply charged ions are produced in the Auger decay process. These ions tend to neutralize their charge when embedded in an environment. We demonstrate that, depending on the atom or molecule and its neighbors, electron transfer mediated decay (ETMD) provides a particularly efficient neutralization pathway for the majority of the ions produced by Auger decay. The mechanism is rather general. As a showcase example, we conducted an ab initio study of the NeKr2 cluster after core ionization of the Ne atom. This example has been chosen because it is amenable to both ab initio calculations and coincidence experiments. We find that even for frozen nuclei, the neutralization rate can be as fast as 0.130 ps(-1). We also show that nuclear dynamics may increase the rate by about an order of magnitude. The generality of the mechanism makes this neutralization pathway important in weakly bonded environments.

Intercomparison of dose enhancement ratio and secondary electron spectra for gold nanoparticles irradiated by X-rays calculated using multiple Monte Carlo simulation codes

“…Such a positively charged nanoparticle is highly reactive and may extract electrons from neighboring water and other biomolecules. This neutralization process can drive energy transfers and charge transfers [46], which are ultra-fast relaxation processes that may ionize surrounding molecules and produce slow electrons, thereby amplifying radiation damage beyond that predicted by Auger decay alone [47].…”

Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets

“…Like in ICD, the original version of ETMD applies to ions which possess sufficient excess energy to ionize their neighbors. In sharp contrast to both cases, recently, a new variant of ETMD has been disclosed which does not require excess energy and can even be triggered from the ground state [16]. Recently, Stumpf et al [17] predicted ETMD to dramatically enhance (∼ 3 orders of magnitude) the single photon double ionization of a Mg atom in the vicinity of a He atom.…”

“…Like in ICD, the original version of ETMD applies to ions which possess sufficient excess energy to ionize their neighbors. In sharp contrast to both cases, recently, a new variant of ETMD has been disclosed which does not require excess energy and can even be triggered from the ground state [16].…”

The role of metal ions in X-ray-induced photochemistry

“…As a result, ETMD is usually observed if the decaying state does not have enough excess energy to decay by ICD [17,18]. This was specifically demonstrated to be the case for multiply charged ions produced in clusters by the Auger decay process [19].…”