Local Electric Fields in Aqueous Electrolytes

Chad I. Drexler, Olivia M. Cracchiolo, Ryan L. Myers, Halil I. Okur, Arnaldo L. Serrano, Steven A. Corcelli, Paul S. Cremer

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Vibrational Stark shifts were explored in aqueous solutions of organic molecules with carbonyl- and nitrile-containing constituents. In many cases, the vibrational resonances from these moieties shifted toward lower frequency as salt was introduced into solution. This is in contrast to the blue-shift that would be expected based upon Onsager's reaction field theory. Salts containing well-hydrated cations like Mg2+ or Li+ led to the most pronounced Stark shift for the carbonyl group, while poorly hydrated cations like Cs+ had the greatest impact on nitriles. Moreover, salts containing I- gave rise to larger Stark shifts than those containing Cl-. Molecular dynamics simulations indicated that cations and anions both accumulate around the probe in an ion- and probe-dependent manner. An electric field was generated by the ion pair, which pointed from the cation to the anion through the vibrational chromophore. This resulted from solvent-shared binding of the ions to the probes, consistent with their positions in the Hofmeister series. The "anti-Onsager"Stark shifts occur in both vibrational spectroscopy and fluorescence measurements.

Original languageEnglish (US)
Pages (from-to)8484-8493
Number of pages10
JournalJournal of Physical Chemistry B
Volume125
Issue number30
DOIs
StatePublished - Aug 5 2021

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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