HF dissociation in water clusters by computer simulations

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Title: HF dissociation in water clusters by computer simulations
Authors: Elena, Alin Marin
Advisor: Ciccotti, Giovanni
Meloni, Simone
Permanent link: http://hdl.handle.net/10197/6782
Date: 2013
Online since: 2015-08-12T08:33:24Z
Abstract: We perform Restrained hybrid Monte Carlo simulations to compute the equilibrium constant of the dissociation reaction of HF in HF(H<sub>2</sub>O)<sub>7</sub>. We find that, like in the bulk, hydrofluoric acid, is a weak acid also in the cubic HF(H<sub>2</sub>O)<sub>7</sub> cluster, and that its acidity is higher at lower T. This latter phenomenon has a (vibrational) entropic origin, namely it is due to the reduction of the (negative) T&#8710;S contribution to the variation of free energy between the reactant and product. We found also a temperature dependence of the reactions mechanism. At low T (&le;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), first two hydrogen atoms move together, forming an intermediate metastable state having the structure of an Eigen ion H<sub>9</sub>O<sub>4</sub><super>+</super>, then the third hydrogen migrates completing the reaction. We also compute the dissociation rate constant, k<sub>rp</sub>. We find that at very low T (&le;75 K), k<sub>rp</sub> depends strongly on the temperature, while it is almost constant at higher Ts. With respect to the bulk, the HF dissociation in HF(H<sub>2</sub>O)<sub>7</sub> is about one order of magnitude faster. This is due to a lower free energy barrier for dissociation in the cluster.
Type of material: Doctoral Thesis
Publisher: University College Dublin. School of Physics
Qualification Name: Ph.D.
Copyright (published version): 2013 the author
Keywords: ClusterDeprotonationFree energyHFRare events
Other versions: http://dissertations.umi.com/ucd:10000
Language: en
Status of Item: Peer reviewed
Appears in Collections:Physics Theses

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