INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
Positional Isotope Exchange in HX·(H2O)n (X = F, I) Clusters at Low Temperatures
JAVIER RODRIGUEZ ; YAIR LITMAN; DANIEL LARIA; PABLO VIDELA
JOURNAL OF PHYSICAL CHEMISTRY A
AMER CHEMICAL SOC
Lugar: Washington; Año: 2016 vol. 120 p. 7213 - 7213
We present Molecular Dynamics simulation results describingproton/deuteron exchange equilibria along hydrogen bonds atthe vicinity of HX acids (X = F, I) in aqueous clustersat low temperatures.To allow for an adequate description of proton transfer processes,our simulation scheme resorted on the implementation of aMultistate Empirical Valence Bond Hamiltonian coupled to aPath Integral scheme to account for effects derived from nuclearquantum fluctuations.We focused attention on clusters comprising a number of water moleculesclose to the threshold values necessaryto stabilize contact-ion-pairs. For X=F, our resultsreveal a clear propensity of the heavy isotope to lie at thebond bridging the halide to the nearest water molecule. Contrasting, for X=I, the thermodynamicstability is reversed and the former connectivity is preferentially articulated viathe light isotope. These trends remain valid for undissociatedand ionic descriptions of the stable valence bond states.The preferences are rationalized in terms of differences in the quantumkinetic energies of the isotopes which, in turn, reflect the extent of thelocal spatial confinements prevailing along the different hydrogen bonds inthe clusters. In most cases, these features are also clearly reflectedin the characteristics of the corresponding stretching bands of the simulatedinfrared spectra. This opens interesting possibilitiesto gauge the extent of the isotopic thermodynamic stabilizations and the strengths of thedifferent hydrogen bonds byfollowing the magnitudes and shifts of the spectral signals in temperature controlledexperiments, performed on mixed clusters combining H_2O and HOD.