Periodic Reporting for period 4 - ETMD_ICEC (Efficient pathways to neutralization and radical production enabled by environment) Reporting period: 2021-04-01 to 2022-09-30 Summary of the context and overall objectives of the project The project was devoted to the investigation of two processes – electron-transfer mediated decay (ETMD) and interatomic Coulombic electron capture (ICEC). The major goals of the project were 1) to develop the theory and computational methods for studying ETMD and ICEC, and 2) to uncover the potential inherent to ETMD and ICEC and exploit it. These objectives were fully accomplished and the investigation of ICEC, and especially of ETMD, is now a rapidly growing field of research. Stimulated by our results, a number of experimental groups from all over the world have performed experiments and are now actively working on studying and exploiting the different aspects of these processes. During the project, our team developed a palette of theoretical and computational methods and techniques allowing high-quality calculations for obtaining static and dynamic properties of the ETMD and ICEC processes in different systems ranging from small van-der-Waals clusters to doped helium droplets and microsolvated atoms and molecules. Using these tools, we were able to elucidate various aspects of the studied processes and predict new mechanisms from the non-local decay family. Our collaborations with several experimental groups were strongly intensified, giving rise to a series of spectacular experiments on the subject, confirming the important role the ETMD mechanism plays in distributing energy and charges to the environment after a local deposition of ionizing radiation. Inspired by these results, other experimental groups entered the field and performed and/or are currently preparing new experiments on the subject. We found that ETMD is an important pathway for the neutralization of multiply charged ions produced in an Auger decay in condensed media and demonstrated for the first time the existence of de-excitation cascades that consist of several non-local decay processes, including different variants of ETMD, which distribute the initially deposited energy to the environment, creating secondary electrons and radical cations. These relaxation pathways are expected to be ubiquitous in biomatter and important for understanding the radiation damage. We also developed an ab initio approach allowing to compute ICEC cross sections in experimentally interesting systems and showed that the process can be highly efficient in mirosolvated atoms and molecules, additionally enhanced by the electronic resonances of the solvent. In addition, we formulated and investigated theoretically a new vibrational energy transfer process, which accelerates the rate of vibrational relaxation in molecules in the presence of atomic or molecular anions by several orders of magnitude. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far The major scientific achievements can be summarized as follows:- We found that ETMD is an important pathway for the neutralization of multiply charged ions produced in the Auger decay in condensed media. First experiments have already confirmed this results and several are have been currently analyzed or are in preparation.- The ETMD process shows an extreme efficiency in doped helium droplets. A number of experiments have already been performed in helium droplets doped with alkali metal dimers showing that the ETMD rate and spectra are very sensitive to the electronic structure of the dopant.- Our high-level calculation of the ICEC cross section in a microsolvated ion showed that the electronic resonances of the molecular neighbor play an important role in the electron capture process. In particular, the electron can be temporarily captured by a water neighbor and donated back to the positive ion in an ETMD-like process. We expect this mechanism to play an important role in the commonly observed neutralization of metal ions at the catalytic centers of enzymes subjected to X-ray radiation. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) Our work on interatomic decay processes in the framework of the current project has led also to the identification of novel interatomic relaxation processes, which are important in molecules separated by several Angstroms. We found that vibrational energy can be very efficiently exchanged between moving nuclei of one molecule and weakly bound electrons of another at distances at which no bond between the two molecules is possible. A molecule can also dissociate by the energy transferred from a remote excited neutral or ionic atom or molecule. Electron-transfer mediated decay Interatomic Coulombic electron capture Vibrational to electronic energy transfer
