Electronic Excitation Dynamics

Published in the Journal of the American Chemical Society, Ph.D. student Dillon Yost and Professor Yosuke Kanai report their quantum-mechanical study of electronic excitation dynamics in DNA under proton irradiation.

Electronic excitations are produced when matter is exposed to ion irradiation comprising highly energetic ions. These electronic stopping excitations are responsible for ion beam-induced DNA damage by energetic protons and α-particles, the chemistry and physics of which are central to burgeoning radiation cancer therapies. By simulating non-linear electronic response of DNA to irradiating protons and α-particles, their first-principles dynamics simulations revealed unprecedented details of the quantum dynamics of electronic excitation.

This work discusses the extent to which the linear response theory can be employed by comparing it to their first-principles determination of electronic stopping power, and the energy-transfer rate from ions to electronic excitation. The simulations show that electronic excitations induced by proton and α-particle irradiation cause ionization of DNA, resulting in the generation of excited holes within.

The work reveals remarkable differences in the excitation behavior of DNA to the case under more commonly used ionizing irradiations such as X/γ-ray photons. Interestingly, it was found that the generation of excited holes does not directly correlate with the energy transfer rate as a function of the irradiating ion velocity. The work is supported by NSF grants and the DOE’s INCITE award.