LAUSR

Abstract With the aid of differential phonon spectrometrics (DPS) and surface stress detection, we show that HI and NaI solvation transforms different fractions of the H O stretching phonons from the mode of ordinary water centred at ∼3200 to the mode of hydration shell at ∼3500 cm −1 . Observations suggest that an addition of the H ↔ H anti-hydrogen-bond to the Zundel notion, [H(H 2 O) 2 ] + , would be necessary as the H O bond due H 3 O + has a 4.0 eV energy, and the H ↔ H fragilization disrupts the solution network and the surface stress. The I − and Na + ions form each a charge centre that aligns, stretches, and polarize the O:H O bond, resulting in shortening the H O bond and its phonon blue shift in the hydration shell or at the solute-solvent interface. The solute capabilities of bond-number-fraction transition follow: f H  = 0, f Na  ∝ C, and f I  ∝ 1 − exp(−C/C 0 ) toward saturation, with C being the solute molar concentration and C 0 the decay constant. The f H  = 0 evidences the non-polarizability of the H + because of the H ↔ H formation. The linear f Na (C) suggests the invariance of the Na + hydration shell size because of the fully-screened cationic potential by the H 2 O dipoles in the hydration shell but the nonlinear f I (C) fingerprints the I −  ↔ I − interactions at higher concentrations. Concentration trend consistency between Jones–Dole’s viscosity and the f NaI (C) coefficient may evidence the same polarization origin of the solution viscosity and surface stress.