Bandwidth analysis of solvation dynamics in a simple liquid mixture

Abstract

The time-dependent energy distribution of solvation dynamics is studied by molecular dynamics simulations of a Lennard-Jones mixture. We calculate the response functions of the average and the variance which correspond to the spectral peak shift and bandwidth. Our calculation shows that the variance relaxation is slower than that of the average. The result agrees qualitatively with the experimental results. Dividing the obtained response functions into subcomponents caused by each solvent, we find that the relaxation is dominated by that solvent which strongly interacts with the solute. Extracting the redistribution component from the response functions, we find that it causes the slower relaxation of the response function. Thus, we conclude that the difference of the slower relaxations between the average and variance is caused by the redistribution process.

Preferential solvation dynamics in liquids: How geodesic pathways through the potential energy landscape reveal mechanistic details about solute relaxation in liquids

“…9,14,19,20,22,24,25,38 Mixed solvents suddenly confronted by an electronically excited solute seem to evolve two fundamentally separate ways. Slow preferential solvation is not specific to hydrogen bonding solvents or to the presence of strong electrostatic forces, for example.…”

“…The specific model, which was proposed and investigated by Sakurai and Yoshimori,20 consists of N s "strong" solvents ͑S͒, N w "weak" solvents ͑W͒, and a single solute ͑u͒ capable of being in either a ground ͑g͒ or excited ͑e͒ electronic state, all interacting by Lennard-Jones pair potentials, u ␣␤ ͑r͒ = 4 ␣␤ ͓͑/r͒ 12 − ͑/r͒ 6 ͔, ͑␣,␤ = u-g,u-e,S,W͒.…”

“…In single-component solvents, ultrafast solvation is largely governed by the dynamics of the first solvation shell, and, in particular, in dipolar solvents, by first shell librational motions. 9,[18][19][20][21] That some kind of translational diffusion process lies at the heart of slow preferential solvation is now widely accepted. However, solvent mixtures have an extra translational option because of the possibility of replacing one kind of solvent in the first shell with another ͑"redistribution"͒.…”

How a solute-pump/solvent-probe spectroscopy can reveal structural dynamics: Polarizability response spectra as a two-dimensional solvation spectroscopy

“…The system we study here is the same one outlined in a number of earlier papers: 10,22,23 an atomic liquid mixture consisting of a single solute (u) and mixture of strongly (S) and more-weakly (W) solvating solvent atoms. All of the atoms have identical masses m and interact via identical LennardJones potentials whenever the solute is in its ground electronic state (u-g), but when the solute is promoted to its excited electronic state (u-e), the solute-solvent attractions increase, and they do so differentially for the S and W solvents u ab (r) = 4ε ab [(σ ab /r) 12 − (σ ab /r) 6 As simple as this system is, it showcases the classic phenomenology of preferential solvation, [67][68][69] Fig.…”

“…We show, first, that one can calculate the full two-dimensional spectra theoretically from a molecular dynamics simulation, and second, that when the calculated spectra are studied for a system that does undergo major structural rearrangements (in our case, an atomic liquid mixture exhibiting preferential solvation), 10,22,23 the resulting spectra unmistakably do track some of the explicitly structural correlation functions computed from the simulation -correlation functions whose dynamics are measurably different from what would have been seen in time-dependent fluorescence.…”