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Efficient pathways to neutralization and radical production enabled by environment

Periodic Reporting for period 3 - ETMD_ICEC (Efficient pathways to neutralization and radical production enabled by environment)

Reporting period: 2019-10-01 to 2021-03-31

The project is devoted to the investigation of two ultrafast electronic relaxation processes -- Electron transfer mediated decay (ETMD) and interatomic Coulombic electron capture (ICEC). ETMD of positive ions in their ground or the lowest excited electronic states was identified as a very efficient relaxation mechanism in chemical media. It is an important component of a general charge redistribution phenomenon, which describes the spread of positive charge throughout an extended system. ICEC is an efficient capture mechanism for slow electrons. Both charge redistribution and slow electrons are responsible for radiation damage in molecules. The problem of radiation damage is central to the fields of structural biology and radiation therapy. Understanding the underlying mechanisms and determining the efficiencies of the damaging processes are, therefore, of utmost importance. The two major goals of this project are the development of the theory and computational methods for studying ETMD and ICEC, and uncovering the potential inherent to ETMD and ICEC and exploiting it.
In the first period, we made a considerable effort to identify ETMD in the experimentally relevant systems and to provide theoretical assistance to experimentalists who investigated this process. A number of large-scale experiments were performed fully confirming our theoretical predictions. ETMD was clearly demonstrated in rare gas clusters, and its study led to better understanding of the chain of ultrafast relaxation process set off by ionizing radiation. Its identification in solutions and hydrogen bonded systems has proved to be more difficult. Due to the complexity of such biologically relevant environment, the experiments proceed in stages. While ETMD was demonstrated in a groundbreaking experiment in LiCl solution, so far mostly the processes such as Auger decay and interatomic Coulombic decay, which like ETMD are parts of relaxation cascades, were investigated. In addition, in an important step to studying electron capture in chemical media we developed an ab initio approach, which allows us to compute ICEC cross sections in experimentally amenable systems. The work on the interatomic decay also led to the theoretical formulation of 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.
IWe project that continuing collaboration with the experimental groups will uncover ETMD in more of biologically relevant systems, such as hydrogen bonded clusters and water solutions, while ongoing research in rare gas clusters would lead to further improvement of our understanding of the ETMD mechanism. We also expect that our theoretical investigations of ICEC, using the newly developed method, will identify suitable systems and thus stimulate first experimental search for this process.
Electron-transfer mediated decay
Interatomic Coulombic electron capture