Shock-tube methods

A general limitation of the relaxation teclmiques with small perturbations from equilibrium discussed in the previous section arises from the restriction to systems starting at or near equilibrium under the conditions used. This limitation is overcome by teclmiques with large perturbations. The most important representative of this class of relaxation techniques in gas-phase kinetics is the shock-tube method, which achieves J-jumps of some 1000 K (accompanied by corresponding P-jumps) [30, and 53]. Shock hibes are particularly... 

The overall stoichiometric equation for this decomposition leading to equilibrium depends on the temperature. A considerable amount of the final products are H, OH, and O. Bauer et al.3 were the first to report an investigation of the water dissociation by the shock-tube method. The temperature range for this study was 2400-3200 °K. They followed the reaction by measuring the uv absorption of the hydroxyl radical produced during the decomposition. The apparent activation energy for the parameter (1/ [H20])(d [OH]/df) of about 50 kcal.mole-1 seemed to indicate that the reaction... 

The single-pulse shock tube method in the thermal decomposition of l,l,l-trifluoro-2-chloroethane gave parallel eliminations135. The major reaction involved HC1 elimination which was believed to be formed by an a,a-elimination (equation 45) with a concerted transfer of a fluorine atom, while to a lesser extent a slower a,/Felimination of HF also took place (equation 46). 

As well as conventional kinetic methods, the shock-tube method and the toluene vapour-flow method have also been used for studying the unimolecular elimination of hydrogen iodide from alkyl iodides. Table 12 summarises Arrhenius Parameters for these reactions. 

The techniques of infrared emission, ultraviolet and visible absorption and emission, and time-of-flight mass spectrometry have also been utilized and will be discussed along with a general description of the shock tube method and various methods of data reduction and refinement. 

Different experimental techniques, including static pyrolysis, carrier (flow) techniques, shock tube methods, and very-low-pressure-pyrolysis, have been used to measure hunt as a function of temperature and pressure. One of the most significant achievements of RRKM theory is its ability to match measurements of kum with pressure. 

Recent advances in the measurement of high-temperature reaction rate constants are discussed. The studies carried out by shock tube methods are particularly considered because these results are important not only in theoretical chemical kinetics but also in practical applications. The work on five chemical reactions are reviewed in detail. These are D +... 

When the reaction time is less than 1 msec, flow methods are too slow to insure homogeneity. Shock tube methods are useful for studying high-temperature gas-phase reactions which take place in time spans of 1 msec to 1 [jLsec. Here a driver gas (usually He or Hg at a few atmospheres pressure) is constrained by a diaphragm at one end of a long tube the remainder of the tube is filled with reactant mixture at low pressure (typically 10 atm). When the diaphragm is ruptured the driver gas expands abruptly. 

In the shock-tube method a reaction vessel is constructed with two chambers separated by a diaphragm that can be ruptured suddenly. On one side is a mixture of gaseous... 

Some techniques were presented for studying fast reactions that cannot be studied by classical experimental techniques. These techniques included continuous flow and stopped-flow techniques, which are rapid mixing methods, as well as relaxation techniques. The relaxation techniques included shock-tube methods, flash photolysis, and T-jump and P-jump methods. Equations were derived for the relaxation of a reaction after a small perturbation, giving an exponential relaxation for a variety of rate laws. 

Hashimoto, K., Matsunaga, N., Nagashima, A., and Mito, K., Determination of the Thermal Conductivity of Xenon-Helium Mixtures at High Temperatures by the Shock Tube Method , International Journal of Thermophysics, 13 (2), 211-221, 1992. Kestin, J., Khalifa, H. E., and Wakeham, W. A., The Viscosity and Diffusion Coefficients of Binaty Mixtures of Xenon With Other Noble Gases, Physica A, 90 (2), 215-228,1978. 

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