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

Sun, Xiang; Stratt, Richard M.

doi:10.1063/1.4816373

Cited by 10 publications

(15 citation statements)

References 81 publications

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“…Water solvation dynamics induced by a sudden change in the charge distribution of a solute within it has been the object of much research over the years, including both experiment 1-12 -primarily via dynamic Stokes shifts in time-dependent fluorescence -and theory -including both analytic modeling [13][14][15][16][17][18][19] and computations [20][21][22][23][24][25][26][27][28][29][30] (see Ref. 31 for a recent review).…”

Section: Introductionmentioning

confidence: 99%

Translational versus rotational energy flow in water solvation dynamics

Rey

Hynes

2017

Chemical Physics Letters

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Early molecular dynamics simulations discovered an important asymmetry in the speed of water solvation dynamics for charge extinction and charge creation for an immersed solute, a feature representing a first demonstration of the breakdown of linear response theory. The molecular level mechanism of this asymmetry is examined here via a novel energy flux theoretical approach coupled to geometric probes. The results identify the effect as arising from the translational motions of the solute-hydrating water molecules rather than their rotational/librational motions, even though the latter are more rapid and dominate the energy flow.Postprint (author's final draft

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Section: Introductionmentioning

confidence: 99%

Translational versus rotational energy flow in water solvation dynamics

Rey

Hynes

2017

Chemical Physics Letters

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“…In response to the change of the dipole moment of the solute, solvent molecules surrounding the photoexcited solute molecules are rearranged ,,− and thus can contribute to the ultrafast response of the TRXL signal. Previously, such photoinduced solvation in liquid solutions has been intensively studied in the field of solvation dynamics using time-resolved spectroscopy. ,,− ,,,− The temperature and density of the bulk solvent would also change in the dye solution, but the q -space profile of the TRXL signal arising from such a change is well characterized from the previous TRXL studies and therefore can be separated from other contributions, as will be discussed later. In addition to the above contributions, the transient alignment of solvent molecules by interactions with the polarized electric field of optical pump pulse, which is known to be the origin of the OKE phenomenon, ,− , can also contribute to the ultrafast response of the TRXL signal of the dye solution (and even the neat solvent), as will be discussed below.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Interaction-induced motion has been known to contribute to the OKE signal on the intermediate time scale ranging from sub-picoseconds to picoseconds. ,, Orientational diffusion is a rather slow collective rotation of individual molecules and is responsible for the slow decay of the OKE signal on the picosecond time scale. These assignments of the molecular motions associated with the OKE signal on various time scales rely on theoretical simulations, such as a molecular dynamics (MD) simulation combined with instantaneous normal mode (INM) analysis, ,,− rather than the direct observation of the motions in real space mainly due to the lack of an experimental means to directly visualize the evolution of the collective molecular rearrangement in solution. In fact, instead of the molecular-level theoretical simulations, analytical methods based on theoretical models such as the mode-coupling theory, Kubo’s discrete random jump model, and the multimode Brownian oscillator model have also been developed .…”

Section: Introductionmentioning

confidence: 99%

Optical Kerr Effect of Liquid Acetonitrile Probed by Femtosecond Time-Resolved X-ray Liquidography

Choi

Kim

et al. 2021

J. Am. Chem. Soc.

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Optical Kerr effect (OKE) spectroscopy is a method that measures the time-dependent change of the birefringence induced by an optical laser pulse using another optical laser pulse and has been used often to study the ultrafast dynamics of molecular liquids. Here we demonstrate an alternative method, femtosecond time-resolved X-ray liquidography (fs-TRXL), where the microscopic structural motions related to the OKE response can be monitored using a different type of probe, i.e., X-ray solution scattering. By applying fs-TRXL to acetonitrile and a dye solution in acetonitrile, we demonstrate that different types of molecular motions around photoaligned molecules can be resolved selectively, even without any theoretical modeling, based on the anisotropy of two-dimensional scattering patterns and extra structural information contained in the q-space scattering data. Specifically, the dynamics of reorientational (libration and orientational diffusion) and translational (interaction-induced motion) motions are captured separately by anisotropic and isotropic scattering signals, respectively. Furthermore, the two different types of reorientational motions are distinguished from each other by their own characteristic scattering patterns and time scales. The measured time-resolved scattering signals are in excellent agreement with the simulated scattering signals based on a molecular dynamics simulation for plausible molecular configurations, providing the detailed structural description of the OKE response in liquid acetonitrile.

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“…The analysis adopted here is also reminiscent of instantaneous NMs which have been shown to perform well for the short-time dynamics in the condensed phase. − Furthermore, a direct comparison between instantaneous NMs, scanning (“scan”) along the NM, and map-based frequency trajectories have been recently presented and found that “NM” and “scan” yield comparable FFCFs and 1D line shapes derived from them …”

Section: Methodsmentioning

confidence: 99%

Multipolar Force Fields for Amide-I Spectroscopy from Conformational Dynamics of the Alanine Trimer

et al. 2021

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The dynamics and spectroscopy of N-methyl-acetamide (NMA) and trialanine in solution are characterized from molecular dynamics simulations using different energy functions, including a conventional point charge (PC)-based force field, one based on a multipolar (MTP) representation of the electrostatics, and a semiempirical DFT method. For the 1D infrared spectra, the frequency splitting between the two amide-I groups is 10 cm −1 from the PC, 13 cm −1 from the MTP, and 47 cm −1 from self-consistent charge density functional tight-binding (SCC-DFTB) simulations, compared with 25 cm −1 from experiment. The frequency trajectory required for the frequency fluctuation correlation function (FFCF) is determined from individual normal mode (INM) and full normal mode (FNM) analyses of the amide-I vibrations. The spectroscopy, time-zero magnitude of the FFCF C(t = 0), and the static component Δ 0 2 from simulations using MTP and analysis based on FNM are all consistent with experiments for (Ala) 3 . Contrary to this, for the analysis excluding mode−mode coupling (INM), the FFCF decays to zero too rapidly and for simulations with a PC-based force field, the Δ 0 2 is too small by a factor of two compared with experiments. Simulations with SCC-DFTB agree better with experiment for these observables than those from PC-based simulations. The conformational ensemble sampled from simulations using PCs is consistent with the literature (including P II , β, α R , and α L ), whereas that covered by the MTP-based simulations is dominated by P II with some contributions from β and α R . This agrees with and confirms recently reported Bayesian-refined populations based on 1D infrared experiments. FNM analysis together with a MTP representation provides a meaningful model to correctly describe the dynamics of hydrated trialanine.

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

Cited by 10 publications

References 81 publications

Translational versus rotational energy flow in water solvation dynamics

Translational versus rotational energy flow in water solvation dynamics

Optical Kerr Effect of Liquid Acetonitrile Probed by Femtosecond Time-Resolved X-ray Liquidography

Multipolar Force Fields for Amide-I Spectroscopy from Conformational Dynamics of the Alanine Trimer

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