Time-dependent density-functional study of intermolecular Coulombic decay for 2a1 ionized water dimer

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Intermolecular Coulombic decay (ICD) is a key process following ionization of molecules.
• Understanding ICD dynamics is crucial for molecular physics and chemistry.
• Water dimer is a fundamental system for studying intermolecular interactions and decay processes.

Purpose of the Study:

• To investigate intermolecular Coulombic decay (ICD) in a water dimer following inner-valence electron ionization.
• To explore the role of nuclear motion and proton transfer in ICD dynamics.
• To differentiate decay mechanisms based on vacancy location within the water dimer.

Main Methods:

• Real-space, real-time time-dependent density functional theory (TD-DFT) with Ehrenfest dynamics.
• Simultaneous treatment of electronic and nuclear motions.
• Analysis of electronic excitation, charge transfer, ionization, and nuclear dynamics.

Main Results:

• Simulations confirm ICD following ionization of the 2a1 state in the water dimer.
• A novel dynamical process involving initial proton back-and-forth motion was identified.
• Two distinct pathways were observed: one with no proton transfer, and another with complete proton transfer.
• When the vacancy is in the proton acceptor, only ICD occurs without proton transfer.

Conclusions:

• The location of the inner-valence electron vacancy significantly influences the decay dynamics in water dimers.
• Proton transfer is a viable pathway coupled with ICD when the vacancy is in the proton donor.
• The employed TD-DFT approach accurately captures complex coupled electronic-nuclear dynamics in ICD processes.