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FAST REACTION (Relaxation Techniques (Flash Photolysis Method (Flash…
FAST REACTION
Relaxation Techniques
Shock-wave Method
The shock tube technique has been proven to be a very powerful method for investigating gas phase reactions at high temperatures
With shock tubes, the experimental pressure (0.1-1000 bar) and temperature (500-15000 K) can be easily varied over a wide range
To increase the translational and rotational temperature of a gas by a definite amount in a time of the order of a few collision times
Flash Photolysis Method
Flash Photolysis is often used to study reactions that are light dependent such as photosynthesis and reactions in the cones on the retina of the our eye, but the method can also be applied to other reactions
A pump-probe laboratory technique, in which a sample is firstly excited by a strong pulse (called pump pulse) of light from a pulsed laser of nanosecond, picosecond, or femtosecond pulse width or by another short-pulse light source such as a flash lamp
This first strong pulse is called the pump pulse and starts a chemical reaction or leads to an increased population for energy levels other than the ground state within a sample of atoms or molecules
Typically the absorption of light by the sample is recorded within short time intervals (by a so-called test or probe pulses) to monitor relaxation or reaction processes initiated by the pump pulse
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Flow Techniques
Continuous-Flow Method
A type of assay used to easily measure the progress of a reaction at discrete time points and is commonly used for determining initial rates and inhibition values
The composition of the reaction is measured continuously, normally by absorbance, while the reactants flow and mix continuously
Offers a high degree of accuracy by allowing what amounts to a large number of readings at each time point, since the reactant mixture at one point is measured multiple times as it passes the sample point
Stopped-Flow Method
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This technique involves two reactants held in separate reservoirs that are prevented from freely flowing by syringe pumps. The reaction is initiated by depressing the reactant syringes, and thus releasing the reactants into the connecting "mixing chamber" where the solutions are mixed
The Stopped Flow technique works because within milliseconds of combining the two reactants the absorbance can be read. In addition, the stop syringe assures for a steady rate of flow pass the spectophotometer so that reactants are being added to solution and forming products at a consistant rate