Sum Frequency Generation of Water on NaCl, NaNO₃, KHSO₄, HCl, HNO₃, and H₂SO₄Aqueous Solutions

Abstract

The vapor−liquid interface of aqueous inorganic acid and salt solutions are examined using sum frequency generation (SFG). The results show that the SFG intensity of hydrogen-bonded water on 0.01x acid (HCl, HNO3, and H2SO4) solutions, where x = mole fraction, is greatly enhanced compared to the 0.01x solution of the corresponding salts (NaCl, NaNO3, and KHSO4). This suggests that either surface water molecules on the acid solutions orient with the dipole in a more vertically aligned fashion than those on the salt solutions or that more layers of water are ordered. These results are interpreted with an electric double layer model, in which the double layer is composed of subsurface anions and cations. The weak association of protons, as opposed to Na+ or K+, with anions results in a greater electric field at the surface on acid solutions. The perturbation of surface water on ionic solutions is discussed in terms of electrostatic and displacement mechanisms.

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.…”

“…Molecular dynamics simulations, 45,[84][85][86] surface sensitive spectroscopy studies, 21,33,[87][88][89] and surface tension measurements 6,85 have been used to examine nitrate ions in solution, and most have concluded that in bulk aqueous solutions of NaNO 3 (Z 300 water molecules), nitrate is not in surface excess compared to the bulk. In bulk nitrate ion photolysis, O À and NO 2 formed via reaction (1a) have a high recombination rate due to solvent cage effects, thus regenerating nitrate ion.…”

Structure of the nanobubble clusters of dissolved air in liquid media

“…), i.e., the specific local properties of the liquid were by no means taken into account; here we speak about the dipole moments and polarizabilities of molecules, and their sizes. The subsequent numerous theoretical works allowed for the geometrical characteristics of water molecule [27], numerical MD simulation in the view of the effect of polarization of water molecules [28][29][30][31][32][33][34][35][36][37][38], and also series of experimental results including vibrational sum frequency generation spectroscopy [39][40][41][42][43][44], second harmonic generation spectroscopy [45,46], high-pressure VUV photoelectron spectroscopy [47,48], and X-ray photoelectron spectroscopy combined with scanning electron microscopy [49,50] allow us to make a conclusion about an opportunity of adsorption of some anions, for example, Cl − , I − and Br − on the watergas interface. The fact that basically negative ions are capable of adsorption at this interface is also supported by the data obtained in Ref.…”

Spectroscopic evidence for the specific Na+ and K+ interactions with the hydrogen-bonded water molecules at the electrolyte aqueous solution surfaces

“…[38,39,40,41,42,46] It has been known that addition of the electrolytes into the bulk aqueous phase can introduce changes in the ssp SFG spectra in the hydrogen-bonded water region, i.e. 3000- [3,6,17,18,24,39,47] In order to systematically investigate the anion effects on the hydrogen-bonded water molecules at the electrolyte aqueous solution surfaces, the ssp 3 SFG-VS spectra of the NaF, NaCl, NaBr and NaI slat solution surfaces were measured by two independent groups. [17,24] Their SFG-VS data on the NaCl, NaBr and NaI aqueous solution surfaces agreed well with each other.…”

“…[1,2,3,4,5] Recently, there have been a great deal of theoretical and experimental studies on the ion solvation and ion effects at the electrolyte aqueous solution surfaces. [1,2,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] Ions have long been considered to be depleted from the surface of an aqueous solution of simple electrolytes, such as the alkali halides. [30,31,32] According to the Gibbs adsorption equation, the increase of the surface tension of water with the addition of simple inorganic salts was explained by the assertion that the simple ions can only have a negative adsorption at the aqueous interface.…”