Theoretical understanding on the v(1)-SO4(2-) band perturbed by the formation of magnesium sulfate ion pairs.
The factors determining the spectroscopic characteristics of the v(1)-SO4(2-) band of the MgSO4 ion pairs are discussed via ab initio calculation, including coupling effect, hydrogen bonding effect, and direct contact effect of Mg2+ with SO4(2-). With the calculation of the heavy water hydrated contact ion pairs (CIP), the overlap between the librations of water and the v(1)-SO4(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)-SO4(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 Mg2+ and the sulfate ion makes the v(1)-SO4(2-) band blue shift of 3.7 cm(-1). When the outer-sphere water around Mg2+ are hydrogen bonded between SO4(2-) and Mg2+, it will make the largest disturbance to the v(1)-SO4(2-) band. Moreover, the inner-sphere water can affect the v(1)-SO4(2-) band conjunct with the direct contact of Mg2+ with SO4(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.
Zhang
Hao
H
The Institute for Chemical Physics, Beijing Institute of Technology, Beijing, China 100081.
Zhang
Yun-Hong
YH
Wang
Feng
F
D003198:Computer Simulation; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry; D008278:Magnesium Sulfate / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D011789:Quantum Theory; D013431:Sulfates / Q000737:chemistry*; D014732:Vibration
D007477:Ions; D013431:Sulfates; D008278:Magnesium Sulfate