The dynamics and spectroscopic fingerprint of hydroxyl radical generation through water dimer ionization: Ab initio molecular dynamic simulation study

Water decomposition process was investigated by ab initio molecular dynamic simulations using a model of (H₂O)₂⁺ clusters. The proton transfer (PT) process from the cationic H-donor water to the H-acceptor water for the formation of (HO)·H₃O⁺ was predicted as about 90 fs on average calculated at CCSD level of theory. The valence-electron transfer (VET) process through the formation of hemibond interaction between neutral and cationic water, (H₂O) ₂⁺, was also identified in several collected trajectories. Both PT and VET processes were found to propagate along two orthogonal reaction coordinates, the former was through an intermolecular hydrogen bond and the latter required oxygen-oxygen hemibonding. Significant difference of the theoretical electronic transitions along the VET trajectories was also observed in comparison with the non-VET cases, being calculated at SAC-CI level. The strong absorption features of hemibonding (H₂O)₂ ⁺ may introduce an interesting consideration for experimental design to monitor the water decomposition process.