Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

Charge migration (CM) is a coherent attosecond process that involves the movement of localized holes across a molecule. This phenomenon is potentially useful to understand the fundamental principles of photochemistry, such as light harvesting. The first part of this dissertation discusses the molecular modes of attosecond charge migration. In this work, we used first-principles calculations to investigate the modes of charge migration (CM) in halogenated hydrocarbon chains at attosecond timescales. We have simulated the creation of a localized hole on the halogen atom using constrained density functional theory (DFT) and then tracked its subsequent dynamics with time-dependent DFT (TDDFT). Our findings reveal low-frequency CM modes (∼ 1 eV) that propagate across the molecule, and we have explored their relationship with the molecule’s length, bond order, and halogenation. Our findings indicates that the CM speed (∼ 4 ˚A/fs) is not significantly impacted by the molecule’s length, but it is slower for triple-bonded molecules than for double-bonded ones. Furthermore, we have observed that as the halogen mass increases, the hole moves in a more particle-like fashion while traversing the molecule. These insights will be valuable for the identification of molecules and optimal CM detection methods for future experiments, particularly for halogenated hydrocarbons, which present promising targets for CM triggered by ionization. The second part of the dissertation discusses the attochemistry principle of charge migration. The study explores how the structure of a molecule affects the CM dynamics it displays. To do this, real-time TDDFT was used to examine para-functionalized bromobenzene molecules (Br−C6H4−R). By simulating rapid strong-field ionization, a localized hole was created on the bromine atom, triggering a CM event that occurs in about 1 fs. The process follows an X localized → C6H4 delocalized → R localized mechanism. Interestingly, the contrast of the hole on the acceptor functional group increases with the group’s electron-donating strength. This trend is accurately described by the Hammett sigma value of the group, which is widely used to measure the effect of functionalization on the chemical reactivity of benzene derivatives. These findings suggest that a density based approach and simple attochemistry principles can be used to anticipate and understand CM.

Date

1-2-2024

Committee Chair

Lopata, Kenneth A.

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