We prepare shock waves in gases, using tubes of aluminium or stainless steel with a constant cross section, which are divided into a high pressure part and a low pressure part by an aluminium membrane at two thirds of the tube length. The reaction gas mixture is inserted in the low pressure part, and afterwards the high pressure part is filled with hydrogen as driving gas until the membrane bursts. The resulting shock wave builds within some tube diameters a flat front that travels through the test gas mixture, heating it adiabatically.
In combination with time resolved UV absorption spectroscopy, we use shock waves for the analysis of high temperature reaction kinetics and for the determination of high temperature spectra of e.g. aromatic compounds and their transient reaction products. Thermally induced reactions can be analysed over a wide range of temperatures and pressures by these means.
As light source, we use either a high pressure xenon arc lamp or a titanium:sapphire laser system. The xenon lamp provides a broad spectrum, which allows us to measure time resolved absorption spectra of reacting systems using a CCD camera as well as to record the absorbance at a specified wavelength with a photomultiplier tube. With the frequency tripled Ti:Sa laser beam, the signal/noise ratio can be improved by comparison with a reference beam.
For experiments with substances that have a very low vapour pressure at room temperature, the whole shock tube can be kept at an elevated temperature of up to 100 °C.
