A 10 kHz laser-induced fluorescence system for time-resolved detection of reactive intermediates via proxy measurements

We present a high-repetition-rate laser-induced fluorescence (LIF) instrument operating at 10 kHz for measuring reaction kinetics of species that dissociate to produce LIF-detectable products. The technique employs a tunable dye laser to excite OH radicals with fluorescence detected by a photomultiplier tube, providing 100 μs temporal resolution. The high repetition rate enables rapid accumulation of thousands of laser shots, achieving high sensitivity and excellent signal-to-noise ratios. We demonstrate this proxy detection approach by monitoring Criegee intermediates (CIs) through their unimolecular decomposition to OH radicals, where the OH temporal profile directly reflects CI decay kinetics. The method is validated using the well-characterized syn-CH3CHOO + SO2 reaction in a flow reactor, yielding rate coefficients consistent with literature values. This technique extends conventional LIF measurements to species that are not directly detectable but produce LIF-active fragments upon decomposition, offering a sensitive, time-resolved approach for studying reactive intermediates with applications in atmospheric and combustion chemistry.