Theoretical understanding on the v1-SO band perturbed by the formation of magnesium sulfate ion pairs
✍ Scribed by Hao Zhang; Yun-Hong Zhang; Feng Wang
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 401 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0192-8651
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
The factors determining the spectroscopic characteristics of the v~1~‐SO~4~^2−^ band of the MgSO~4~ ion pairs are discussed via ab initio calculation, including coupling effect, hydrogen bonding effect, and direct contact effect of Mg^2+^ with SO~4~^2−^. With the calculation of the heavy water hydrated contact ion pairs (CIP), the overlap between the librations of water and the v~1~‐SO~4~^2−^ band can be separated, and thus the coupling effect is abstracted, and this coupling effect leads to a blue shift for the v~1~‐SO~4~^2−^ band of 5.6 cm^−1^ in the monodentate CIP and 3.6 cm^−1^ in the bidentate CIP. The hydrogen bonding between each water molecule without relation to Mg^2+^ and the sulfate ion makes the v~1~‐SO~4~^2−^ band blue shift of 3.7 cm^−1^. When the outer‐sphere water around Mg^2+^ are hydrogen bonded between SO~4~^2−^ and Mg^2+^, it will make the largest disturbance to the v~1~‐SO~4~^2−^ band. Moreover, the inner‐sphere water can affect the v~1~‐SO~4~^2−^ band conjunct with the direct contact of Mg^2+^ with SO~4~^2−^, showing a blue shift of 14.4 cm^−1^ in the solvent‐shared ion pair, 22.6 cm^−1^ in the monodentate CIP, 4.3 cm^−1^ in the bidentate CIP, and 21.4 cm^−1^ in the tridentate CIP. At last, the Raman spectral evolution in the efflorescence production process is tried to be rationalized. The shoulder at 995 cm^−1^ is attributed to the monodentate CIP with 2–3 outer‐sphere water molecules, whereas the new peak at 1021 cm^−1^ at high concentration is assigned to the formation of aqueous triple ion. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009