Investigation of photophysical processes as the basis for quantitative imaging of gas-phase mixing processes with tracer LIF

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The aim of this research project is the improvement of the photophysical understanding of the molecular fluorescence of organic tracer (pairs) as well as the characterization of fluorescence properties in an extended parameter range (temperture, pressure, bath gas composition) and the collection of extended datasets in a web database (TracerSim). Quantitative time- and spatially resolved observation of mixing processes in the gas phase is important for optimizing of, e.g., gas-phase-synthesis or combustion processes. For this purpose, organic molecules are often used as fluorescence tracers in imaging diagnostics (tracer laser-induced fluorescence, tracer-LIF) to determine the quantitative information of interest (e.g., temperature or mixing quality) since fluorescence properties are sensitive to the environmental conditions. The insight generated in this research project can then be used the improvement of diagnostics methods through a better understanding of the underlying photophysics. For this purpose, the second funding period focuses on the following topics:a) In the past years, two or more tracers were used simultaneously for the combined determination of several quantities in mixtures. It has been repeatedly stated that the interaction of the excited molecules is not sufficiently understood to be able to interpret the measured signal intensities without errors. Now, this lack of knowledge will be filled by characterizing and modeling the tracer-tracer interaction under controlled conditions. Furthermore, the results on self-quenching and on the influence of the excitation wavelength gained in the first funding period, which showed to be important for the application of tracer LIF in practical situations will be validated using further practically-relevant tracers.b) The fluorescence properties determined in the first funding period as well as newly measured data for further tracers will be included into the already partially implemented web-based TracerSim database. This database will be further refined and will facilitate the usability of the collected photophysics data and will thus contributes to a better usage of tracer-LIF in the entire research community.c) The new results of this project will be implemented into established photophysical fluorescence quantum yield models to improve the data interpretation capabilities and to extend their applicability to further species, not investigated so far. The models will be integrated into the TracerSim web database for interpolation and extrapolation. Furthermore, an analysis tool for experimental tracer-LIF data will be implemented.