Reactions associated with ionization in water: a direct ab initio dynamics study of ionization in (H2O)17
A quasi-classical ab initio dynamics calculation of the (H2O)17 cluster, which is the first water cluster that includes a four-fold coordinated water molecule, has been carried out to obtain a detailed picture of the elementary processes and energy redistribution induced by ionization in a model of aqueous water. Well within 100 fs after ionization, a proton is seen to have transferred from the “ionized molecule” to a neighboring molecule, forming a hydronium ion and a hydroxyl radical. Two neighboring water molecules to the ionized water molecule play an important role in the reaction, in what we term a “reactive trimer”. The reaction time is gated by the encounter of the “ionized” water molecule with these two neighboring molecules and this occurs at ~ 35 fs after ionization. We find that the distance of approach between the “ionized” molecule and the neighboring molecule reflects best the time characteristics of the transfer of a proton, and thus of the formation of a hydronium ion and an OH radical. These findings are consistent with those for smaller cyclic clusters, albeit the dynamics of the transferring proton is much damped in our simulation compared to the small cyclic cluster cases. We use a partitioning scheme for the kinetic energy of the << OLE Object: Microsoft Equation 3.0 >> system that distinguishes the “reactive trimer” and the surrounding medium. The analysis of the simulation indicates that the kinetic energy of the surrounding medium increases markedly right after the event of ionization. The increase in kinetic energy is consistent with a reorganization of the surrounding medium, in this case an orientation relaxation, from a configuration as a hydrogen bond donor to the “ionized” tetra-coordinated water molecule, into a configuration where the surrounding water molecule have turned their dipoles for a more favorable interaction with the “ionized” water cation. Battelle operates the Pacific Northwest National Laboratory for the US Department of Energy.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 882102
- Report Number(s):
- PNNL-SA-47719; JCPSA6; 3566; KC0301020; TRN: US200613%%594
- Journal Information:
- Journal of Chemical Physics, 124:164310, Vol. 124; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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