# Ultrafast Optical Kerr Effect Spectroscopy Reveals the Vibrational Fingerprint of Acetate–Water Hydrogen Bonds

## TL;DR

This study uses ultrafast spectroscopy to identify the unique vibrational signature of hydrogen bonds between acetate and water, offering insights into hydration and electrolyte behavior.

## Contribution

The paper introduces a new vibrational fingerprint for acetate–water hydrogen bonds using ultrafast OKE spectroscopy.

## Key findings

- Acetate solutions show a distinct vibrational band near 200 cm–1 absent in methyl acetate.
- The observed band is independent of the countercation and distinct from other anion–water vibrations.
- Quantum-chemical calculations confirm the vibrational mode assignment.

## Abstract

Time-resolved optical Kerr effect (OKE) spectroscopy
was employed
to investigate the low-frequency vibrational dynamics of aqueous acetate
solutions. While the isotropic OKE spectrum of neat water is broad
and featureless, acetate solutions display a distinct band near 200
cm–1. This feature increases systematically with
acetate concentration, is absent in methyl acetate, and shows negligible
dependence on the countercation, establishing it as the vibrational
fingerprint of acetate–water hydrogen bonds. Comparison with
hydroxide solutions demonstrates that the band is spectrally distinct
from other anion–water vibrations. Quantum-chemical calculations
further support the assignment, reproducing polarized vibrational
modes in the same frequency region. Together, these results resolve
long-standing ambiguities in the interpretation of acetate hydration
and highlight the power of ultrafast OKE spectroscopy to isolate solute-specific
hydrogen-bond vibrations in aqueous solutions. Beyond spectroscopy,
these findings have implications for understanding electrolyte behavior
in energy storage systems (e.g., lithium-ion batteries) and biological
buffering processes.