Kjær, Kasper Skov1; Brandt van Driel, Tim4; Kehres, Jan1; Haldrup, Martin Kristoffer1; Khakhulin, Dmitry8; Bechgaard, Klaus6; Cammarata, Marco7; Wulff, Michael8; Sørensen, Thomas Just6; Nielsen, Martin Meedom1
1 Department of Physics, Technical University of Denmark2 Neutrons and X-rays for Materials Physics, Department of Physics, Technical University of Denmark3 Experimental Surface and Nanomaterials Physics, Department of Physics, Technical University of Denmark4 Risø National Laboratory for Sustainable Energy, Technical University of Denmark5 European Synchrotron Radiation Facility6 University of Copenhagen7 Université de Rennes8 European Synchrotron Radiation Facility
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.
Physical Chemistry Chemical Physics, 2013, Vol 15, Issue 36, p. 15003-15016