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Raman spectroscopy of alkali halide hydration: hydrogen bond relaxation and polarization
- Source :
- Journal of Raman Spectroscopy. 47:1351-1359
- Publication Year :
- 2016
- Publisher :
- Wiley, 2016.
-
Abstract
- The solute–solvent interaction of salts has a striking impact on various biological and industrial processes but its mechanism remains yet mysterious despite intensive studies since 1888 when Franz Hofmeister established the salt series. A combination of confocal Raman spectroscopy and contact angle measurements has enabled us to resolve the hydrogen bond relaxation (O:H―O, HB) and the associated charge polarization dynamics at different molecular site because of alkali halides hydration. Results show consistently that salt hydration softens the O:H phonon but stiffens H―O phonon cooperatively. The extent of HB relaxation and polarization is proportional to the electronegativity difference and ionic radius, following the order of Hofmeister series: X (R/η) = I (2.2/2.5) > Br (1.96/2.8) > Cl (1.81/3.0) > F (1.33/4.0) ≈ 0 for anions, and Y(R/η) = Na (0.98/0.9) > K (1.33/0.8) > Rb (1.49/0.8) > Cs (1.65/0.8) for cations. Observations suggest that ions create each an electric field that aligns, stretches, and polarizes water molecules, which relaxes the O:H―O bond cooperatively, depresses the molecular dynamics, and enhances the hydration shell viscosity and the skin stress. Exercises also demonstrate that Raman spectroscopy performs as a powerful tool for probing the molecular-site-resolved HB network relaxation dynamics in terms of phonon stiffness, molecular fluctuation dynamics, and phonon abundance transition under external stimulus. Copyright © 2016 John Wiley & Sons, Ltd.
- Subjects :
- Ionic radius
Hofmeister series
Chemistry
Hydrogen bond
Phonon
02 engineering and technology
010402 general chemistry
021001 nanoscience & nanotechnology
01 natural sciences
0104 chemical sciences
Electronegativity
symbols.namesake
Solvation shell
Computational chemistry
symbols
Physical chemistry
Molecule
General Materials Science
0210 nano-technology
Raman spectroscopy
Spectroscopy
Subjects
Details
- ISSN :
- 03770486
- Volume :
- 47
- Database :
- OpenAIRE
- Journal :
- Journal of Raman Spectroscopy
- Accession number :
- edsair.doi...........5aab857bb2b7cc38eacb66c8b8af0a3b