2018, Richter, Clemens, Hollas, Daniel, Saak, Clara-Magdalena, Förstel, Marko, Miteva, Tsveta, Mucke, Melanie, Björneholm, Olle, Sisourat, Nicolas, Slavíček, Petr, Hergenhahn, Uwe

Intermolecular Coulombic decay (ICD) is a ubiquitous relaxation channel of electronically excited states in weakly bound systems, ranging from dimers to liquids. As it is driven by electron correlation, it was assumed that it will dominate over more established energy loss mechanisms, for example fluorescence. Here, we use electron–electron coincidence spectroscopy to determine the efficiency of the ICD process after 2a1 ionization in water clusters. We show that this efficiency is surprisingly low for small water clusters and that it gradually increases to 40–50% for clusters with hundreds of water units. Ab initio molecular dynamics simulations reveal that proton transfer between neighboring water molecules proceeds on the same timescale as ICD and leads to a configuration in which the ICD channel is closed. This conclusion is further supported by experimental results from deuterated water. Combining experiment and theory, we infer an intrinsic ICD lifetime of 12–52 fs for small water clusters.

2017, You, D., Fukuzawa, H., Sakakibara, Y., Takanashi, T., Ito, Y., Maliyar, G G., Motomura, K., Nagaya, K., Nishiyama, T., Asa, K., Sato, Y., Saito, N., Oura, M., Schöffler, M., Kastirke, G., Hergenhahn, U., Stumpf, V., Gokhberg, K., Kuleff, A.I., Cederbaum, L.S., Ueda, K

Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne2+ produced after Ne 1s photoionization in Ne-Kr mixed clusters.