TY - JOUR
T1 - Rapid water dynamics structures the OH-stretching spectra of solitary water in ionic liquids and dipolar solvents
AU - Palchowdhury, Sourav
AU - Mukherjee, Kallol
AU - Maroncelli, Mark
N1 - Funding Information:
This work was supported by the U.S. Department of Energy, Office of Basic Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under Award No. DE-SC0019200. Any opinions, findings, conclusions, or recommendations expressed here were those of the authors and do not necessarily reflect the views of the DOE. The authors also acknowledge helpful discussions with Hyung Kim and Fangyong Yan throughout the course of this work.
Publisher Copyright:
© 2022 Author(s).
PY - 2022/8/28
Y1 - 2022/8/28
N2 - In a recent study [J. Phys. Chem. B 126, 4584-4598 (2022)], we have used infrared spectroscopy to investigate the solvation and dynamics of solitary water in ionic liquids and dipolar solvents. Complex shapes observed for water OH-stretching bands, common to all high-polarity solvents, were assigned to water in several solvation states. In the present study, classical molecular dynamics simulations of a single water molecule in four ionic liquids and three dipolar solvents were used to test and refine this interpretation. Consistent with past assignments, simulations show solitary water usually donates two hydrogen bonds to distinct solvent molecules. Such symmetrically solvated water produces the primary pair of peaks identified in the OH spectra of water in nearly all solvents. We had further proposed that additional features flanking this main peak are due to asymmetric solvation states, states in which only one OH group makes a hydrogen bond to solvent. Such states were found in significant concentrations in all of the systems simulated. Simulations of the OH stretching spectra using a semiclassical description and the vibrational map developed by Auer and Skinner [J. Chem. Phys. 128, 224511-224512 (2008)] provided semi-quantitative agreement with experiment. Analysis of species-specific spectra confirmed assignment of the additional features in the experimental spectra to asymmetrically solvated water. The simulations also showed that rapid water motions cause a marked motional narrowing compared with the inhomogeneous limit. This narrowing is largely responsible for making the additional features due to minority solvation states manifest in the spectra.
AB - In a recent study [J. Phys. Chem. B 126, 4584-4598 (2022)], we have used infrared spectroscopy to investigate the solvation and dynamics of solitary water in ionic liquids and dipolar solvents. Complex shapes observed for water OH-stretching bands, common to all high-polarity solvents, were assigned to water in several solvation states. In the present study, classical molecular dynamics simulations of a single water molecule in four ionic liquids and three dipolar solvents were used to test and refine this interpretation. Consistent with past assignments, simulations show solitary water usually donates two hydrogen bonds to distinct solvent molecules. Such symmetrically solvated water produces the primary pair of peaks identified in the OH spectra of water in nearly all solvents. We had further proposed that additional features flanking this main peak are due to asymmetric solvation states, states in which only one OH group makes a hydrogen bond to solvent. Such states were found in significant concentrations in all of the systems simulated. Simulations of the OH stretching spectra using a semiclassical description and the vibrational map developed by Auer and Skinner [J. Chem. Phys. 128, 224511-224512 (2008)] provided semi-quantitative agreement with experiment. Analysis of species-specific spectra confirmed assignment of the additional features in the experimental spectra to asymmetrically solvated water. The simulations also showed that rapid water motions cause a marked motional narrowing compared with the inhomogeneous limit. This narrowing is largely responsible for making the additional features due to minority solvation states manifest in the spectra.
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U2 - 10.1063/5.0107348
DO - 10.1063/5.0107348
M3 - Article
C2 - 36050016
AN - SCOPUS:85137105751
SN - 0021-9606
VL - 157
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 8
M1 - 084502
ER -