Isotopic Preferential Solvation of I- in Low Temperature Water Nanoclusters

PABLO VIDELA; PETER J. ROSSKY; LARIA, DANIEL HECTOR

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Lugar: Washington; Año: 2015 vol. 119 p. 11783 - 11790

1520-6106

We present results from ring-polymer-molecular-dynamics experiments thatprovide microscopic insights into the characteristics of the isotopicstabilizations of H and D aqueous species in the first solvation shell of ahalide I$^-$, in water nanoclusters at low temperatures.  The analysis of thesimplest I$^-cdot$(HOD) dimer shows a clear propensity forthe light isotope to lie at the non-hydrogen bonded dangling position. Ourresults predict that, at $Tsim 50$ K, I$^-cdot$(DOH) isomers are three timesmore abundant than I$^-cdot$(HOD) ones. The reasons for such stabilizationcan be traced back to differences in the nuclear kinetic energy projectedalong directions perpendicular to the plane of the water molecule.  Dynamicalimplications of these imbalances are shown to be reflected in the characteristicsof the corresponding bands of the infrared spectroscopic signals.A similar analysis performed in larger aggregates containing $sim 20$water molecules reveals, in contrast,  a stabilization of the light isotopealong ${m I^-cdots HO}$ hydrogen bonds.  Effects derived from the considerationof smaller Halide anions with larger electric fields at the surface are also examined.