Work Group Prof. Dr. F. Temps

Kinetics of Radical-Molecule and Radical-Radical Reactions in the Gas Phase

Kinetics of Elementary Reactions by Time-Resolved Mass Spectrometry

Laser photolysis reactor with time-resolved mass spectrometer

Time-resolved studies of the kinetics of elementary chemical reactions are required for developing complex reaction mechanisms and modeling practically important chemical processes, such as combustion, atmospheric chemistry, chemical vapor deposition, and exhaust gas cleaning technologies. We have developed a very versatile experimental setup by coupling excimer laser photolysis for producing specific radicals with time-resolved mass spectrometric detection. A recently studied reaction is HO2 + C2H5 = OH +  C2H5O, an important chain branching step leading to engine knock.

  

 

Shock Tube Studies of High Temperature Reactions

Shock tube (with cw dye laser in front)

The shock tube technique is a very powerful method for investigating gas phase reactions at high temperatures. A shock wave propagates along the shock tube at supersonic speed and heats and compresses the test gas within less than 1 μs (incident shock wave). The shock wave is reflected at the end wall and passes through the test gas once more (reflected shock wave). Our shock tube is designed for investigating the elementary reactions of small radicals (e.g., NH2, HCO, SiH2, 1CH2) at temperatures of 700 K < T < 3500 K and pressures of 0.75 bar < p < 3.5 bar. Radicals are detected by FM and UV absorption spectroscopies.

 

  

NOx-Reburning

Kinetics of the reaction CH2+NO

"NOx-Reburning" is a technically important process for the reduction of NO in power plants and engines. Trace amounts of hydrocarbons are injected into the exhaust gases. The NO thus reacts with small hydrocarbon radicals and is recycled into the oxidation chain. Two of the main reburn reactions of NO are those with CH2 and with HCCO.  We have studied these reactions using Laser Magnetic Resonance (LMR) and Fourier-Transform Infrared (FTIR) spectroscopies, ab initio quantum chemistry and density functional theory, and unimolecular rate theory.

 

 

 

Cavity Ringdown Spectroscopy

Cavity ringdown spectrometer

Cavity ringdown spectroscopy (CRDS) is an ultra-sensitive laser based absorption technique. The high detection sensitivity is primarily based on the long absorption length (>10 km) arising from a multiple reflection of a laser pulse in the optical cavity formed by two highly reflective mirrors. Moreover, CRDS is inherently immune to intensity fluctuations of the laser pulses, and enables one to determine absolut concentrations. The molecular absorption is directly related to the lifetime of the exponential "ringdown" of the signal that is transmitted through the cavity. We employ CRDS in the visible and the near IR (around 1.6 μm) for measuring free radical reactions and for surface studies.

 

  

Kinetics of Si Containing Radicals

Kinetics of Si containing radicals

 

 

 

 

   

Radical-Radical Kinetics by ab initio Quantum Chemistry and Unimolecular Rate Theory

Kinetics of the reaction CH2+NO