Theoretical Investigation of the Effect of Intermolecular Interactions on the Spectrum of Doubly Ionized States in Uracil-nH2O (n = 1-4) Systems

The formation of radical-cation states with vacancies in inner-valence levels upon the effect of ionizing radiation on biological systems can initiate electron-emission relaxation processes. Ionization of the initial molecule with the formation of the dicationic state corresponds to the Auger decay. If molecules of the nearest environment are ionized, then it is the intermolecular Coulombic decay (ICD). Recent studies show that intermolecular interactions, including those with a solvent, are an important factor determining the probability of such relaxation processes and their energy characteristics. DNA and RNA nucleic bases are known to have some amount of water molecules in their nearest environments. In this work, using the equation-of-motion method in the EOM-DIP-CCSD variant, we consider the effect of the number of water molecules and their orientations in uracil complexes (U) U–nH₂O, n = 1-4 on the spectrum of dicationic states formed by the described processes. It is shown that the lowest energies of ICD states are due to water coordination to uracil at positions most characteristic of RNA. The energy of states with vacancies on different molecules decreases with increasing number of water molecules from 1 to 3, and then remains invariant. The number of ICD dicationic states increases with increasing number of environment molecules, which indicates the significant role of nonlocal decays in solution.