Near infrared cw-CRDS coupled to laser photolysis: Spectroscopy and kinetics of the HO2 radical

We present in this work a new experimental set-up for sensitive detection of reactive species: continuous wave cavity ring-down spectroscopy (cw-CRDS) as a detection method in laser photolysis reactor. HO₂ radicals were generated by using a 248 nm photolysis of SOCl₂/CH₃OH/O₂ mixtures and were detected in the first vibrational overtone of the OH stretch around 6625 cm^-1, using a DFB diode laser. In order to perform the spectroscopic and kinetic measurements of the HO₂ radical, two different timing schemes have been used. The absorption line strength of the transition at 6625.784 cm^-1 has been extracted from kinetic measurement to (5.2±1.0)×10^-21 cm² molecule^-1cm^-1. The detection limit for the actual set-up is 2×10¹² molecules cm^-3. PACS 42.62.Fi; 82.33.Tb; 82.20.W