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/O-2 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)x10(-21) cm(2) molecule(-1)cm(-1). The detection limit for the actual set-up is 2x10(12) molecules cm(-3).