Reaction selectivity in an ionized water dimer: nonadiabatic ab initio dynamics simulations

Area of Science:

• Physical Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• Water dimer radical cations are crucial in atmospheric and biological processes.
• Understanding their reaction dynamics is key to predicting chemical behavior.

Purpose of the Study:

• To investigate state-dependent reactivity in water dimer radical cations.
• To map potential energy surfaces (PESs) for different electronic states.
• To elucidate dynamical pathways and product distributions.

Main Methods:

• Nonadiabatic dynamical simulations using surface hopping.
• Complete Active Space-Self Consistent Field (CASSCF) for electronic structure.
• Analysis of potential energy surfaces (PESs) and comparison with experimental data.

Main Results:

• Observed proton transfer (H3O(+)···OH˙) and dissociation products (e.g., H3O(+) + OH˙).
• Product yields are controlled by the populated electronic state of the radical cation.
• Ultrafast proton transfer (<100 fs) for HOMO ionization; longer timescales (200-300 fs) for higher energy ionization.

Conclusions:

• Reactivity of water dimer radical cations is strongly state-dependent.
• Simulations provide insights into ultrafast dynamics and product formation.
• Findings have implications for understanding intermolecular coulomb decay (ICD) in water dimer.