TIME-RESOLVED WAVELENGTH MODULATION SPECTROSCOPY MEASUREMENTS OF HO2 KINETICS

High-frequency wavelength modulation spectroscopy (WMS) has been appli ed to the detection of the hydroperoxyl radical (HO2) in a laser photo lysis and long-path absorption pump-probe kinetics reactor with a near -infrared distributed feedback diode laser. The HO2 is formed by the 3 55-nm photolysis of Cl-2 in the presence of CH3OH and O-2 and monitore d by a phase-sensitive detection of the second-harmonic (2f) signal in the 2 upsilon(1) band with a 1.5-mu m diode laser directly modulated at 5 MHz. The measured 2fWMS signal is calibrated by direct absorption and converted to an absolute number density with the known absorption line strength of the HO2 line at 6625.80 cm(-1). The utility of time- resolved WMS as a second-order kinetics probe is demonstrated through the measurement of the HO2 self-reaction rate constant at 295 K. (C) 1 997 Optical Society of America.