Tunable laser flash absorption: a new technique for measuring rates and yields of chemical reactions at high temperatures

The flash absorption technique, whereby light from an excimer laser is used to measure the kinetic behavior of absorbing species in the high temperature region behind a shock front with a linear array detector, has been extended by using tunable light from a high resolution, pulsed dye laser. The use of narrowband, tunable light allows us to access isolated rovibronic transitions and, thereby, obtain state-specific kinetic information. If the oscillator strength of the transition and the absorption line profile are known, the absolute concentration may be determined. We demonstrate the technique by measuring the temporal development of the hydroxyl radical as it is formed after propane has been thermally dissociated in the presence of oxygen. We conclude that accurate kinetic measurements can be made with hydroxyl concentrations of 10(15) cm(-3) This technique may also be applied to study any species which absorbs below 50,000 cm(-1).