Probing Attosecond Photoionization Dynamics and Charge Migration

Arizona State University, Scottsdale AZ

Investigators

Abstract

Advances in laser and x-ray technology have enabled scientists to study quantum processes in atoms, molecules, and materials with unprecedented time resolution. This project will apply x-ray pulses that are shorter in duration than a millionth of a billionth of a second to investigate a fundamental question in quantum physics: how fast is the electron ejected from a molecule hit by a light pulse? The awardee will study the timescale of the electron ejection, and its dependence on the molecular environment. The research team funded by this award will use ultrafast measurements to understand how electrons interact with each other, and how the light-molecule interaction is impacted by the positions of atoms within the molecule. The knowledge gained from this research will facilitate strategies for controlling the flow of charge and energy inside molecules for practical applications in the fields of light harvesting and energy storage. Additionally, it will enhance our understanding of the electronic processes behind DNA damage and vitamin D synthesis, and contribute to the development of ultrafast quantum devices for national security applications. The students engaged in this project will gain cutting-edge technical expertise in ultrafast science and develop scientific proficiency to initiate their own research investigations. This will foster scientific innovation and enhance the competitiveness of our nation in critical research areas. To conduct this research, the research team will employ attosecond extreme-ultraviolet and soft-x-ray pulse techniques to investigate the fundamental topic of photoionization and its novel applications in probing correlated electron processes. In this endeavor, the PI and students will measure the photoionization delays with attosecond interferometry to probe the role of electronic interactions and molecular environment. Additionally, elementally specific transient absorption will be employed to study the charge migration induced by the correlations during photoionization. The team will employ advanced diagnostic techniques, including velocity map imaging and attosecond transient absorption, to conduct these studies. In molecular systems, the photoionization delay measurements will illuminate the effect of shape resonances, electron-nuclear couplings, and non-adiabatic dynamics. Such studies will establish photoionization delay as a highly sensitive probe of many-body dynamics and provide a testing ground for the theoretical models. Correlations in the photoionization process can also mix orbital configurations and create superpositions of ionic states, driving hole migration in large molecules. The localization of the hole charge can subsequently guide the chemical reactivity of the molecule, paving the way for attosecond chemistry. Therefore, the application of attosecond soft-x-ray pulses for spatiotemporal mapping of the charge dynamics in complex systems will serve to establish attosecond science as a versatile spectroscopy technique. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.