Introducing a standard method for experimental determination of the solvent response in laser pump, X-ray probe time-resolved wide-angle X-ray scattering experiments on systems in solution

Abstract

In time-resolved laser pump, X-ray probe wide-angle X-ray scattering experiments on systems in solution the structural response of the system is accompanied by a solvent response. The solvent response is caused by reorganization of the bulk solvent following the laser pump event, and in order to extract the structural information of the solute, the solvent response has to be treated. Methodologies capable of doing so include both theoretical modelling and experimental determination of the solvent response. In the work presented here, we have investigated how to obtain a reproducible solvent response-the solvent term-experimentally when applying laser pump, X-ray probe time-resolved wide-angle X-ray scattering. The solvent term describes difference scattering arising from the structural response of the solvent to changes in the hydrodynamic parameters: pressure, temperature and density. We present results based on NIR and dye mediated solvent heating, and demonstrate that the solvent response is independent of the heating method. The NIR heating is shown to be rendered unusable by higher order effects under certain experimental conditions, while the dye mediated solvent heating is demonstrated to exhibit first order behaviour with respect to the amount of energy deposited in the solution. We introduce a standardized method for recording solvent responses in laser pump, X-ray probe time-resolved X-ray wide-angle scattering experiments by using dye mediated solvent heating. Furthermore, we have generated a library of solvent terms, which can be used to describe the solvent term in any TRWAXS experiment, and made it available online.

Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering

“…Specifically, the observed broadening of the bulk acetonitrile (MeCN) scattering feature at 1.8 Å -1 after time delays >5 ps corresponds to the heating of the solvent (Fig. 1C) [53]. However, for the purposes of the present study, we focus on the structural dynamics associated with changes in the solute and solute-solvent pair distribution functions.…”

“…XES emission energies were calibrated after ground state spectra measured at the Stanford Synchrotron Radiation Lightsource (SSRL). WAXS Q-range was calibrated with the acetonitrile heating signal [53]. WAXS data analysis procedures are described in Ref.…”

Atomistic characterization of the active-site solvation dynamics of a model photocatalyst

“…The difference scattering signal arises from all structural dynamics induced by the laser pump pulse. In the standard analysis formalism222325, Δ S ( Q , t ) is described as the sum of difference scattering components arising from changes in the solute structure32, changes in the solvation cage structure33, and changes in the bulk solvent structure34.…”

“…The signal arising from intramolecular structural dynamics is calculated directly from a large set of DFT-optimized molecular geometries where the Ir–Ir bond length and N-Ir-Ir-N dihedral angle have been systematically varied. Initial predictions of the solvation signal were extracted from quantum mechanical/molecular mechanical simulations, and the signal from the increase in bulk solvent temperature was taken from reference measurements34. Since a host of concurrent excited state structural dynamics are contributing to the difference scattering signal on early time scales, the analysis was optimized through a series of sequential steps, which ensured that overfitting of any one parameter was avoided.…”

Femtosecond X-Ray Scattering Study of Ultrafast Photoinduced Structural Dynamics in Solvated[Co(terpy)2]Biasin1, Driel2, Kjær3 et al. 2016Phys. Rev. Lett.Self Cite9656901View full textAdd to dashboardCite

“…Finally, the bulk-solvent term ∆S solvent (Q) has been shown to be very well described by a linear combination of solvent difference signals, ∂S(Q) ∂T ρ and ∂S(Q) ∂ρ T , which can be measured in separate experiments [33,34]:…”