Aim
Shock tubes are frequently used to study the kinetics of high temperature gas-phase reactions. A shock wave that is initiated by a gas expansion heats the reactive gas mixture within less than a microsecond to temperatures up to several thousand Kelvin. Subsequent reactions are investigated by optical techniques. Highly sensitive and selective spectroscopic methods provide time-resolved atomic and molecular species concentration measurements and enable the investigation of elementary reactions in highly diluted homogeneous gas mixtures without perturbing side-reactions. Special emphasis is placed on the determination of rate coefficients of unimolecular and bimolecular reactions. The spectrum of the investigated species ranges from simple organic to metal-organic molecules which are applied for nanoparticle synthesis and chemical vapor deposition. The data are the basis source for development and validation of reaction mechanisms that are then used for the numerical simulation of reactive flows.

Approach
The shock tube has a total length of 9.2 m an inner diameter of 79 mm. It is divided by an aluminum diaphragm (up to 0.1 mm thickness) into a driver section (3.5 m) and a driven section (5.7 m in length). The reactive gas mixtures are prepared in a stainless-steel mixing vessel. The driver section is filled with H2 until the diaphragm bursts. Pressure sensors measure the shock wave velocities from which the reaction conditions (pressure and temperature) are determined. Additional to the thermal excitations of reactive species, reactive molecular fragments can also be generated via photo-dissociation initiated by ArF excimer laser radiation. Time-resolved species concentrations measurements of molecules and atoms are monitored by a ring dye laser absorption spectroscopy (RDLAS, UV-VIS) and atomic resonance absorption spectroscopy (ARAS, VUV-UV), respectively. Both methods enable a selective and sensitive concentration measurement in the ppm range.

References
Fikri, M.; Makeich, A.; Rollmann, G.; Schulz, C.; Entel, P. J. Phys. Chem. A  112 (2008) 6330-6337.

Contact
Dr. Mustapha Fikri, Mustapha Fikri,  Tel: +49 (0)203 - 379 3037, IVG