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Updated: May 9, 2026

An Introduction to Processing, Fitting, and Interpreting Transient Absorption Data
Published on: February 16, 2024
How a solute-pump∕solvent-probe spectroscopy can reveal structural dynamics: polarizability response spectra as a
1Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
Abstract:
The workhorse spectroscopy for studying liquid-state solvation dynamics, time-dependent fluorescence, provides a powerful, but strictly limited, perspective on the solvation process. It forces the evolution of the solute-solvent interaction energy to act as a proxy for what may be fairly involved changes in solvent structure. We suggest that an alternative, a recently demonstrated solute-pump∕solvent-probe experiment, can serve as a kind of two-dimensional solvation spectroscopy capable of separating out the structural and energetic aspects of solvation. We begin by showing that one can carry out practical, molecular-level, calculations of these spectra by means of a hybrid theory combining instantaneous-normal-mode ideas with molecular dynamics. Applying the resulting formalism to a model system displaying preferential solvation reveals that the solvent composition changes near the solute do indeed display slow dynamics similar to, but measurably different from, that of the solute-solvent interaction--and that this two-dimensional spectroscopy can effectively single out those local structural changes.
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