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The solvation inhomogeneity of sulfur dioxide in 1‐butyl‐3‐methylimidazolium thiocyanate ionic liquid probed by Raman spectroscopy
Author(s) -
Bär Jaciara,
Monezi Natália M.,
Ando Rômulo A.
Publication year - 2018
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.5270
Subject(s) - raman spectroscopy , solvation , ionic liquid , chemistry , thiocyanate , analytical chemistry (journal) , ion , mole fraction , dispersion (optics) , resonance (particle physics) , spectroscopy , ionic bonding , inorganic chemistry , atomic physics , organic chemistry , physics , quantum mechanics , optics , catalysis
The different solvation states of SO 2 in 1‐butyl‐3‐methylimidazolium thiocyanate ionic liquid were probed by the detailed analysis of the SO 2 symmetric stretching mode, ν s (SO 2 ). The band position and linewidth were monitored in function of gas molar fraction, excitation wavelength, and temperature. As expected, the decreasing of the SO 2 molar fraction, X SO2 , from approximately 0.8 to 0.2, leads to a gradual downshift of the ν s (SO 2 ) band, attributed to a more effective charge transfer interaction from thiocyanate anion to SO 2 . Interestingly, at high gas concentrations (X SO2 = 0.8), a gradual downshift of the ν s (SO 2 ) band was noticed as the Raman excitation energy increases, an unexpected behavior because the change in the excitation wavelength in Raman spectroscopy should affect only the band intensities. Such ν s (SO 2 ) Raman dispersion can be understood as a consequence of the distinct charge transfer electronic transition energies associated to different SO 2 solvation states, whose relative band intensities are modulated by resonance Raman conditions. Moreover, the lowering from room temperature to 100 K showed an increasing in the Raman dispersion effect. The temperature dependence was attributed to the strengthening of the cation–anion interaction, responsible for the increasing of SO 2 solvation states distribution. The vibrational spectroscopic data regarding the SO 2 solvation inhomogeneity in ionic liquids are showed for the first time, and it may contribute in the understanding of why such liquids are promising solvents for SO 2 capture.