Role of Nuclear Motion in the Ultrafast Relaxation Dynamics of Inner-Shell Vacancies in Hydrated Pyrrole

Abstract

We employ real-space, real-time time-dependent density functional theory combined with Ehrenfest dynamics to investigate ultrafast intermolecular relaxation following inner-valence ionization in hydrated pyrrole. By treating nuclear and electronic dynamics on an equal footing, this approach captures their strong coupling and enables a fully time-resolved description of electronic excitation, charge transfer, ionization, and structural rearrangement. When an initial vacancy is created in the water 2 s–1 state, the system predominantly undergoes intermolecular Coulombic decay (ICD) and electron-transfer–mediated decay (ETMD), accompanied by significant intermolecular charge transfer between pyrrole and water. In contrast, fixed-nuclei simulations predict that ICD is the only active decay channel. For ionization of the pyrrole N 2s orbital, both ICD and Auger decay channels are observed, whereas neglecting nuclear motion leads to a qualitative change in the relaxation pathway, with Auger decay dominating exclusively. These results demonstrate that nuclear motion plays a decisive role in ultrafast relaxation dynamics. By dynamically modulating intermolecular distances and electronic couplings, it actively drives and reshapes the competition between decay channels, affecting both their efficiency and branching ratios. Overall, the relaxation pathways are governed by the interplay between the initial vacancy localization and coupled electron–nuclear dynamics, providing microscopic insight into energy- and charge-transfer processes in hydrated molecular systems.