Molecular Modes of Attosecond Charge Migration

We discuss recent progress in understanding molecular charge migration (CM), the rapid movement of positively charged holes in a molecule following localized excitation or ionization. We focus our theoretical calculations on questions that are relevant to successful CM experiments. These include: Which molecules are most likely to support CM? Does the manner in which CM is initiated influence how it proceeds? Does CM manifest in generic ways so that its periodicity and visibility can be predicted to follow simple rules?

To address these questions, we use two strategies. First, we use time-dependent density functional theory to simulate CM in halogenated hydrocarbon chains, which have been shown to support the creation of a localized hole either via strong-field or inner-shell ionization [1]. By isolating the low frequency modes we find that the double and triple-bonded molecules all support robust end-to-end CM that progresses via hopping from π bond to π bond. This occurs with a speed that is largely independent of the molecular length, but that is lower for the triple- than for the double-bonded chains. We also find that heavier halogen atoms support CM in which the hole is more localized as it moves along the molecular backbone. Second, we discuss a new way of understanding CM, using tools of non-linear dynamics to study CM in one-dimensional carbon chains. In doing so, we highlight the central role of dynamical electron-electron coupling and synchronization as the engine for CM dynamics and as an alternative to, e.g., few- orbital beating mechanisms that have previously been discussed. We also demonstrate the importance of functionalization and hybridization in synchronizing the dynamics, which would open the way for chemically controlling CM in the future.

References:

[1] A. Folorunso, et al., Phys. Rev. Lett. to appear (2021).