Stark-Einstein law of photochemical equivalence

Stark-Einstein law of photochemical equivalence one photon of radiation can be absorbed only by one molecule [201,202]. 

The Stark-Einstein law of photochemical equivalence is in a sense simply a quantum-mechanical statement of the Grotthuss-Draper law. The Stark-Einstein law (1905) is another example of the break with classical physics. It states that each molecule which takes part in the photochemical reaction absorbs one quantum of the light which induces the reaction that is, one molecule absorbs the entire quantum the energy of the light beam is not spread continuously over a number of molecules. 

The fundamental law of modern photochemistry is the law of photochemical equivalence proposed by Einstein, according to which each molecule taking part in a photochemical reaction first absorbs one quantum of energy (hv) corresponding with the frequency (v) of the radiation absorbed. (Some approach to this conception had been made by Stark in 1908.) This is the primary process in every photochemical reaction. 

In order for a photochemical reaction to occur the radiation must be absorbed, and with the advent of the quantum theory it became possible to understand the relationship between the amount of radiation absorbed and the extent of the chemical change that occurs. It was first realized by A. Einstein (1879-1955) that electromagnetic radiation can be regarded as a beam of particles, which G. N. Lewis (1875-1940) later called photons each of these particles has an energy equal to /iv, where v is the frequency of the radiation and h is the Planck constant. In 1911 J. Stark (1874-1957) and independently in 1912 Einstein proposed that one photon of radiation is absorbed by one molecule. This relationship, usually referred to as Einstein s Law of Photochemical Equivalence, applies satisfactorily to electromagnetic radiation of ordinary intensities but fails for lasers of very high intensity. The lifetime of a moleeule that has absorbed a photon is usually less than about 10 sec, and with ordinary radiation it is unlikely for a molecule that has absorbed one photon to absorb another before it has become deactivated. In these circumstances there is therefore a one-to-one relationship between the number of photons absorbed and the number of excited molecules produced. Because of the high intensity of lasers, however, a molecule sometimes absorbs two or more photons, and one then speaks of multiphoton excitation. 

II) Law of Photochemical Equivalence (Ilnd law of photochemistry). This law was given by Stark in 1909 and in 1913 by Einstein. This states that. 

Plotnikov later took pain in demonstrating [19] that taking the Grotthuss-Draper law in a quantitative sense, that is, that not only light has to be adsorbed, but that the effect is proportional to the radiation absorbed, could replace the Stark-Einstein law, but he obviously missed the point. The equivalence law states much more precisely that absorption of one quantum of light causes one photochemical act. Whether this applies in every single case or, more correctly, which is the mean probability that this statement applies to one type of acts or to another one, and under which conditions it can be affirmed that this applies to a chemical reaction, is another question (see below). That the effect is proportional to the absorbed flux— provided that the terms are properly defined—is obvious. 

The second principle of photochemistry is called the photochemical equivalence law, or the Stark-Einstein law, which states the absorption of light occurs in the quantum unit of photon or one molecule absorbs one photon, and one or less molecule can be photolyzed accordingly. ... 

Einstein photochemical equivalence law PhiYS chem The law that each molecule taking part in a chemical reaction caused by electromagnetic radiation absorbs one photon of the radiation. Also known as Stark-Einstein law Tn.stTn fOd O kem-a kal i kwiv a lans, 16)... 

The photochemical reaction of a material starts with photon absorption. In other words, only the photons absorbed by the molecule can bring about photochemical reactions. This is the first law of photochemistry, also called the Grotthuss-Draper law. The second law of photochemistry is one molecule is activated when one photon is absorbed. This is called the Stark-Einstein photochemical equivalence law. Generally, a particular group in an irradiated molecule absorbs a photon with an appropriate wavelength. When photoabsorption occurs, the molecule in the ground state is... 

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