TY - JOUR
T1 - Vibrational Probe of Aqueous Electrolytes
T2 - The Field Is Not Enough
AU - Lewis, Nicholas H.C.
AU - Iscen, Aysenur
AU - Felts, Alanna
AU - Dereka, Bogdan
AU - Schatz, George C.
AU - Tokmakoff, Andrei
N1 - Funding Information:
This work was supported as part of the Advanced Materials for Energy-Water Systems (AMEWS) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. B.D. acknowledges support from the Swiss National Science Foundation through Postdoc.Mobility Fellowship Grant P400P2_180765.
Funding Information:
This work was supported as part of the Advanced Materials for Energy-Water Systems (AMEWS) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. B.D. acknowledges support from the Swiss National Science Foundation through Postdoc.Mobility Fellowship Grant P400P2_180765.
PY - 2020/8/13
Y1 - 2020/8/13
N2 - In this work, we study the vibrational solvatochromism and dynamics of dilute acetone as a carbonyl probe in simple aqueous electrolytes as a function of salt composition and concentration. We observe a linear dependence of the redshift of the CO stretch mode as a function of concentration for each salt, with the magnitude of the effect scaling with the charge densities of the cations. Using molecular dynamics (MD) simulations, we compare the observed spectral shifts with the electrostatic field distributions imparted on the acetone O, comparing a fixed-charge model and a polarizable model, and find that the experimentally observed frequencies scale linearly with the electric field for a given salt, but there remains a substantial component of the solvatochromism that depends on the identity of the cation and apparently cannot be explained by the electrostatic fields alone. Finally, we use ultrafast 2D IR spectroscopy to study the salt dependence of the solvation dynamics. We observe an anomalous nonmonotonic dependence of the time scale of the dynamics on the salt concentration, which cannot be reproduced by the fluctuations in the electrostatic field determined from MD simulations. These results point to the importance of both electrostatic and nonelectrostatic effects in the vibrational solvatochromism and dynamics in this apparently simple model system.
AB - In this work, we study the vibrational solvatochromism and dynamics of dilute acetone as a carbonyl probe in simple aqueous electrolytes as a function of salt composition and concentration. We observe a linear dependence of the redshift of the CO stretch mode as a function of concentration for each salt, with the magnitude of the effect scaling with the charge densities of the cations. Using molecular dynamics (MD) simulations, we compare the observed spectral shifts with the electrostatic field distributions imparted on the acetone O, comparing a fixed-charge model and a polarizable model, and find that the experimentally observed frequencies scale linearly with the electric field for a given salt, but there remains a substantial component of the solvatochromism that depends on the identity of the cation and apparently cannot be explained by the electrostatic fields alone. Finally, we use ultrafast 2D IR spectroscopy to study the salt dependence of the solvation dynamics. We observe an anomalous nonmonotonic dependence of the time scale of the dynamics on the salt concentration, which cannot be reproduced by the fluctuations in the electrostatic field determined from MD simulations. These results point to the importance of both electrostatic and nonelectrostatic effects in the vibrational solvatochromism and dynamics in this apparently simple model system.
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U2 - 10.1021/acs.jpcb.0c05510
DO - 10.1021/acs.jpcb.0c05510
M3 - Article
C2 - 32687351
AN - SCOPUS:85089617142
VL - 124
SP - 7013
EP - 7026
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
SN - 1520-6106
IS - 32
ER -