Attosecond charge migration following oxygen K-shell ionization in DNA bases and base pairs

Abstract

Core ionization of DNA begins a cascade of events which could lead to cellular inactivation or death. The created core–hole following an impulse inner-shell ionization of molecules naturally decays in the auger timescale. We simulated charge migration (CM) phenomena following an impulsive core ionization of individual DNA bases at the oxygen K-edge which occurs before Auger decay of the oxygen. Our approach is based on real-time time dependent density functional theory (RT-TDDFT). It is shown that the pronounced hole fluctuation observed around bonds of the initial core–hole results in various valence orbital migrations. Also, the same photo-core-ionized dynamics is studied for the related base pairs. We investigate the role of base pairing and H-bonding interactions in the attosecond CM dynamics. In particular, the creation of a core–hole in the oxygen involved in H-bonding leads to an enhancement of charge migration relative to the respective single bases. Importantly, the hole oscillation of the adenine–thymine base pair upon creation of a core–hole at the oxygen, which does not contribute to the donor–acceptor interactions (not H-bonded), decreases compared to the single thymine base. Understanding the detailed dynamics of the localized core–hole initiating CM process would open the way for chemically controlling DNA damage/repair in the future.