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Title:Equilibrium and Rate Constants, and Reaction Mechanism of the HF Dissociation in the HF (H2O) 7 Cluster by ab Initio Rare Event Simulations
Authors:Alin Marin Elena, Simone Meloni, Giovanni Ciccotti, 2013
Abstract: We perform restrained hybrid Monte Carlo (MC) simulations to compute the equilibrium constant of the dissociation reaction of HF in HF(H2O)7. We find that the HF is a stronger acid in the cluster than in the bulk, and its acidity is higher at lower T. The latter phenomenon has a vibrational entropic origin, resulting from a counterintuitive balance of intra- and intermolecular terms. We find also a temperature dependence of the reactions mechanism. At low T (≤225 K) the dissociation reaction follows a concerted path, with the H atoms belonging to the relevant hydrogen bond chain moving synchronously. At higher T (300 K), the first two hydrogen atoms move together, forming an intermediate metastable state having the structure of an eigen ion (H9O4+), and then the third hydrogen migrates completing the reaction. We also compute the dissociation rate constant, kRP. At very low T (≤75 K) kRP depends strongly on the temperature, whereas it gets almost constant at higher T’s. With respect to the bulk, the HF dissociation in the HF(H2O)7 is about 1 order of magnitude faster. This is due to a lower free energy barrier for the dissociation in the cluster.
ICHEC Project:Deprotonation of organic molecules in solution: study of the reaction mechanism and rate by modern techniques for simulating rare events in combination with ab-initio molecular dynamics.
Publication:The Journal of Physical Chemistry A, 2013, 117 (49), pp 13039–13050
URL: http://dx.doi.org/10.1021/jp406982h
Status: Published

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