Characterization of the Influence of Hydrated Ions on the Oxygen-Hydrogen Stretching Vibration of Water by Raman Spectroscopy

• Published in: Analytical letters Vol. 53; no. 13; pp. 2034 - 2046
• Main Authors: Tian, Zhi-xian, Zhang, Xin, Liu, Chang-ling, Meng, Qing-guo, Du, Zeng-feng, Yan, Jun
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 01.09.2020; Taylor & Francis Ltd
• Subjects: Calcium ions; Charge distribution; Dipoles; Hydration; Hydrogen bonding; ion hydration; Ionic crystals; Parameters; Raman spectroscopy; Skewed distributions; skewing parameter; Stretching; Vibration; Water; Water chemistry; water structure
• DOI: 10.1080/00032719.2020.1728294
• ISSN: 0003-2719

The Raman OH stretching vibration band of liquid water is asymmetric and multimode superimposed and is susceptible to variations in salinity, pressure, and temperature. Ions have non-negligible influences on the Raman O-H stretching band of water because these ion-water interactions are stronger than those between water molecules. The determination of molecular-level details of hydration processes remains a great challenge, both experimentally and theoretically. The effects of 11 common ions on the O-H stretching band of liquid water are characterized with a skewing parameter introduced to describe the distortion caused by ion hydration. With increasing salt concentration, the symmetry of the Raman O-H stretching band decreases as the skewing parameter value increases. Therefore, ions primarily break the tetrahedral hydrogen bonding and promote the formation of partly hydrogen-bonded and free water molecules. Additionally, the effects of anions are much stronger than those of cations due to the asymmetric charge distribution in the dipoles of H 2 O. It is revealed that the influences of the common ions on the Raman OH stretching band of water are in the following order: I - > Br - > Cl - > F - , > K + > Na + , and Sr 2+ > Ca 2+ > Mg 2+ . For ions with the same charge, the order of their effects on the Raman O-H stretching band of water is usually the same as the order of their ionic crystal radii but the reverse order of their hydrated radii.