The role of symmetric vibrational modes in the decoherence of correlation-driven charge migration

Due to the electron correlation, the fast removal of an electron from a molecule may create a coherent superposition of cationic states and in this way initiate pure electronic dynamics in which the hole-charge left by the ionization migrates throughout the system on an ultrashort time scale. The coupling to the nuclear motion introduces a decoherence that eventually traps the charge, and crucial questions in the field of attochemistry include how long the electronic coherence lasts and which nuclear degrees of freedom are mostly responsible for the decoherence. Here, we report full-dimensional quantum calculations of the concerted electron-nuclear dynamics following outer-valence ionization of propynamide, which reveal that the pure electronic coherences last only 2-3 fs before being destroyed by the nuclear motion. Our analysis shows that the normal modes that are mostly responsible for the fast electronic decoherence are the symmetric in-plane modes. All other modes have little or no effect on the charge migration. This information can be useful to guide the development of reduced dimensionality models for larger systems or the search for molecules with long coherence times.

Automated summary

Due to electron correlation, the removal of an electron from a molecule can lead to coherent superposition of cationic states, resulting in pure electronic dynamics in which the ionization-induced hole migrates throughout the system in a short time scale. The coupling to nuclear motion introduces decoherence that traps the charge, and it is important to understand the duration of electronic coherence and the dominant nuclear degrees of freedom responsible for decoherence. Quantum calculations of propynamide reveal that electronic coherences last only 2-3 fs before being destroyed by nuclear motion. Symmetric in-plane modes are primarily responsible for fast electronic decoherence, while other modes have little or no effect on charge migration. This information can guide the development of reduced dimensionality models or the search for molecules with long coherence times.