Ions at the Air/Water Interface

Abstract

We present results from theoretical studies of aqueous ionic solvation of alkali halides aimed at developing a microscopic description of structure and dynamics at the interface between air and salt solutions. The traditional view has depicted the air/solution interface of simple electrolytes as being devoid of ions. However, it is now firmly established that polarizable anions, such as the heavier halides, occupy the surface of small to medium sized water clusters. Using a combination of theoretical calculations, including ab initio quantum chemistry, Car-Parrinello molecular dynamics simulations, and primarily molecular dynamics simulations based on polarizable force fields, we present a unified view of the interfacial structure of aqueous ionic clusters and bulk solutions. Indeed, we demonstrate that the heavier halogen anions have a propensity for the interface that is proportional to their polarizabil- * Electronic mail: jungwirt@jh-inst.cas.cz † Electronic mail: dtobias@uci.edu 2

Enhanced Concentration of Polarizable Anions at the Liquid Water Surface: SHG Spectroscopy and MD Simulations of Sodium Thiocyanide

“…[1][2][3][4][5][6][7][8][9] These findings contradict the textbook description of ions being repelled from the interface and the outermost surface layer being devoid of ions. [10][11][12] This conventional wisdom is largely based on macroscopic measurements of the increasing surface tension of aqueous solutions with salt concentration.…”

“…The ions and molecules were placed in a simulation box with dimensions 30 × 30 × 150 Å 3 and periodic boundary conditions were employed. Due to the elongated z-length of the box an infinite liquid slab was formed in the middle of the z-dimension with two planar liquid-vapor interfaces.…”

The Electronic Structure of the Hydrated Proton: A Comparative X-ray Absorption Study of Aqueous HCl and NaCl Solutions

“…The atom positions for each cluster considered were obtained from a MD simulation of 1.2 M NaCl in water at 300 K, where polarization of both the solvent and the solvated ions are explicitly included. 34 As with H 3 O + , only configurations containing one cation and no anions were considered in order to simplify the interpretation of the calculated spectra. Additionally, XA spectra of the central water molecule in 17 molecule pure water clusters, taken from an MD simulation of pure water, 34 and in 17 water molecule/1 Cl -clusters, taken from the 1.2 M NaCl simulation, were calculated.…”

The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts

“…1 However, a combination of computational [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and experimental studies [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] has shown that ions can reside and even be enhanced at the interface.…”