Molecular Theory of Solute-Pump/Solvent-Probe Spectroscopy and Application to Preferential Solvation Dynamics

Sun, Xiang

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Year:: 2014
Contributor:: Sun, Xiang (creator); Stratt, Richard (Director); Doll, Jimmie (Reader); Rose-Petruck, Christoph (Reader); Brown University. Chemistry (sponsor)
Genre:: theses
Subject:: nonlinear spectroscopy; molecular mechanism; linear response theory; instantaneous normal modes; solvent mixture; simulation; Solvation; Structural dynamics; Simulation methods
Extent:: xxiii, 283 p.
DOI: https://doi.org/10.7301/Z0M043R8

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Abstract:: Common resonant spectroscopic methods used to study dynamics in solutions, such as time-dependent fluorescence, share a feature of probing the solute directly, or more precisely the solute-solvent interaction energy. One has to infer how the solvents move from the solute's time-dependent information. By contrast, nonresonant light scattering experiments report on the dynamics of a liquid as a whole, but cannot concentrate on dynamics of any local portion of the solution. A recently demonstrated two-dimensional solute-pump/solvent-probe spectroscopy, a combination of the two approaches mentioned above, enables us to follow the nonequilibrium dynamics of solvents after the solute's electronic excitation. This dissertation is a theoretical attempt at understanding the molecular information behind this kind of spectroscopy. After developing the general linear response theory for these spectra using classical statistical mechanics, I apply the resulting formalism to a preferential solvation model system consisting of an atomic solute dissolved in an atomic-liquid mixture. In the experimentally interesting limit of long solute-pump/solvent-probe delays, the spectra become the differences in light-scattering spectra between solutions with equilibrated ground- and excited-state solutes. The drastically distinctive spectra for various solvents in this limit suggest how changing liquid structure affects intermolecular liquid dynamics and how local a portion of the solvent dynamics can be accessed by the spectra. For the more general nonequilibrium case of the spectra with finite solute-pump/solvent-probe delays, a practical hybrid calculation method combining instantaneous-normal-mode theory with molecular dynamics shows a great advantage in dealing with two-dimensional spectroscopies especially with separated time scales. The full two-dimensional spectra can serve as a solvation spectroscopy capable of distinguishing the structural and energetic solvation dynamics. Calculations of our preferential solvation model indicate that the spectra indeed display the same relaxation profile as the local solvent population changes, which is measurably different from the solute-solvent interaction energetic relaxation measured by time-dependent fluorescence. Thus the two-dimensional spectroscopy effectively singles out structural dynamics of local solvents around the solute.
Notes:: Thesis (Ph.D. -- Brown University (2014)

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Sun, Xiang, "Molecular Theory of Solute-Pump/Solvent-Probe Spectroscopy and Application to Preferential Solvation Dynamics" (2014). Chemistry Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0M043R8

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Theses and Dissertations for the Chemistry department.
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