Gas-phase chemical reactions are important in a wide variety of environments such as combustion, Earth’s atmosphere, and dense interstellar clouds. Modelling such environments requires a detailed understanding of the mechanisms and rate coefficients of key reactions that define the system. In the atmosphere, the oxidation mechanism of volatile organic compounds (VOC) influences on a regional scale the air quality and hence human health. On a global scale it affects the oxidizing capacity of the atmosphere and with this the global climate by controlling the lifetime of greenhouse gases such as methane and formation of tropospheric ozone. Peroxy radicals are key intermediates in all oxidation reactions, however their reactivity is still not well understood. The current project aims at investigating this chemistry using different experimental approaches. Both PIs have set-up worldwide unique techniques dedicated to the sensitive and selective detection of these radicals: Laser photolysis coupled to time-resolved cavity ring down technique in Lille and laser photolysis coupled to time-resolved double frequency comb spectroscopy. In the frame of this project we want to further improve the experimental techniques to even better study key reactions: in Lille we will develop a new double-walled photolysis reactor which can be (a) thermostated to temperatures of atmospheric interest (the current reactor can only be heated) and (b) add a detection path based on broadband UV absorption spectroscopy. In Taiwan, 2 new laser sources will be added to extend the accesible wavelength range for the already existing frequency comb spectroscopy.