In 1967 the Nobel Prize in Chemistry was awarded to Manfred Eigen, Ronald George, George Porter and Wreyford Norrish for their co-discovery of Flash Photolysis in 1949. Flash Photolysis is used extensively to study reactions that happen extremely quickly, even down to the femtosecond depending on the laser that is used. The technique was born out of cameras developed during and shortly after WWII, which were used to take pictures of fast moving planes, rockets, and missiles. Since then the technology of lasers and optics has progressed allowing faster and faster reactions to be studied.
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 meathod can also be applied to other reactions. The light in the form of a laser excites a molecule into a reactive state, usually in the form of a free radical. From there it is possible to measure the reaction spectroscopically, using the exitory flash as a light source to measure absorbance. The laser pulse must be aproximatly half the length of the reaction, and of sufficient energy to induce the reaction to take place. Further the flash must cover the spectrum of frequencies which are being studied because not only is the flash producing intermediates of the reaction that are usually not observed, it is also producing the source for spectroscopic analysis. Intermediates of most reactions are rarely observed, this techniques isolates even low concentrations of otherwise unobservable portions of reactions allowing research into synthetic, biochemical, and photo-sensitive reactions.
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