Department of Physics and Astronomy, Aarhus University, Denmark

Mass spectrometry and fluorescence spectroscopy are powerful techniques on their own, but they can also be integrated into a single instrument, a fluorescence mass spectrometer, capable of detecting fluorescence from mass-selected, photoexcited ions. Only a few such specialized setups exist worldwide. At Aarhus University, my group has constructed two instruments: LUNA (LUminescence iNstrument in Aarhus) and its successor, LUNA2. In the latter case, ions are cooled to liquid-nitrogen temperatures, which can significantly enhance fluorescence quantum yields, especially important for challenging systems. Photoexcitation takes place at the center of a Paul trap, and emitted photons are subsequently detected. Ions are generated by electrospray ionization, enabling studies of large and fragile molecular ions. The resulting absorption and emission spectra that are measured provide highly specific data that inform on the ions’ structure and serve as powerful benchmarks for computational studies. I will present the design and strengths of these instruments through recent examples, including gas-phase Förster Resonance Energy Transfer (FRET), the photophysics of protein biochromophores, and studies in molecular astrochemistry if time allows.