NaX solvation bonding dynamics:hydrogen bond and surface stress transition (X = HSO4, NO3, ClO4, SCN)

Abstract

Raman phonon differential spectrometrics (DPS) and contact angle measurements resolved that solvation of the NaX (X=HSO4, NO3, ClO4, SCN) complex salts stiffens the HO stretching phonon from 3200 to ~3500cm−1 and softens the O:H nonbond phonon from 180 to ~70cm−1 with rising of solution surface stress. The solute capability of bond transition in terms of the fraction coefficient, follows the relation, fNaX(C)∝1-exp(−C/C0) towards saturation, with C being the solute concentration and C0 the decay constant. Observations evidence that: (i) the solute ionic field electrification aligns, stretches, and polarizes its neighboring H2O molecules, which shortens the HO bond but lengthens the O:H nonbond via OO Coulomb repulsion; (ii) the effect of X− electrification on the O:HO bond relaxation varies with solute type and solute concentration. Exercises not only verify the essentiality of solvent O:HO bond cooperative relaxation and polarization but also demonstrate the power of DPS that resolves processes occurred upon solvation.