Abstract

High-frequency wavelength modulation spectroscopy (WMS) has been applied to the detection of the hydroperoxyl radical (HO₂) in a laser photolysis and long-path absorption pump-probe kinetics reactor with a near-infrared distributed feedback diode laser. The HO₂ is formed by the 355-nm photolysis of Cl₂ in the presence of CH₃OH and O₂ and monitored by a phase-sensitive detection of the second-harmonic (2f) signal in the 2ν ₁ band with a 1.5-µm diode laser directly modulated at 5 MHz. The measured 2f WMS signal is calibrated by direct absorption and converted to an absolute number density with the known absorption line strength of the HO₂ line at 6625.80cm^-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.

© 1997 Optical Society of America

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