Stark-Einstein law

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

The Stark-Einstein law states that the primary act of light... 

According to the Stark-Einstein law, O should be equal to 1. However, if secondary reactions occur, can be greater than 1. 

The second law of photochemistry was first enunciated by Stark (1908) and later by Einstein (1912). The Stark-Einstein law states that ... 

The second law is the Stark—Einstein law. whose re-statement in current terminology is that the primary photochemical act involves absorption of just one photon by a molecule. This holds true for the vast majority of processes exceptions to it arise largely when very intense light sources, such as lasers, are employed, and the probability of concurrent or subsequent absorption of two or more photons is no longer negligible. 

Grottus-Draper law, 3 Lambert-Beer law, 3 second law, 5 Stark-Einstein law, 5 (of) metallocenes, 277... 

Photon energies can vary. Only one photon can be accepted at a time by an obtital. This is stated in the Stark-Einstein law also known as the Second Law of Photochemistry—if a species absorbs radiation, then one particle (molecule, ion, atom, etc.) is excited for each quantum of radiation (photon) that is absorbed. 

Stark-Einstein law, 4 Stem-Volmer plot, 34 slilbene, absorption spectrum, 1 3 cis-trans isomerization, 42 cvclization, 97 excited state energies, 17 styrenes, addition reactions, 58... 

The energy of an excited species must go somewhere, so the Stark-Einstein law leads to the conclusion that the sum of the quantum yields for all primary processes, including deactivation, must be unity. Where experimental data are available, this expectation is well substantiated. 

A second important law of photochemistry, known as the Stark-Einstein Law, follows directly from the particle behaviour of electromagnetic radiations. 

Until now we had been talking of gas reactions. Many substances undergo photochemical reactions in liquid state. Again the reaction in initiated by Stark-Einstein law by direct light absorption on the part of reactants. However, it maybe anticipated that quantum efficiency of these reactions will be less than for the same reaction in the gas phase. The reason for this is that in the liquid state an active molecule may readily be deactivated by frequent collisions with other molecules. Furthermore, because of the very short mean free path in the liquid phase free radicals or atoms when formed photochemically will tend to recombine before they have a chance to get very far from each other. The net effect of these processes will be to keep the quantum yield relatively low. In fact, only those reactions may be expected to proceed to any extent for which the primary products of the photochemical act are relatively stable particles. Otherwise the active intermediates will tend to recombine with the solvent and thereby keep the yield low. 

Only light that is absorbed can produce a chemical change, a principle embodied in the Grotthuss-Draper law of photochemistry. This is true whether radiant energy is converted to some other form and then stored or is used as a trigger. Another important principle of photochemistry is the Stark-Einstein law, which specifies that each absorbed photon activates only one molecule. Einstein further postulated that all of the... 

Only light that is absorbed can affect chemical change. The Stark-Einstein law states that one photon is absorbed by each molecule responsible for the primary photochemical process. 

Stark-Einstein law. Every molecule in a chemical reaction induced by exposure to light absorbs one quantum of the radiation causing the reaction. 

The 2nd law of photochemistry, called the Stark-Einstein Law, states that the absorption of light by a molecule is a one-quantum process, so that the sum of... 

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. 

If we define the primary act of the photochemical reaction as the absorption of the quantum, then the quantum efficiency for the primary act is, by the Stark-Einstein law, equal to unity. For each quantum absorbed, one primary act occurs. For any substance X taking part in a photochemical reaction, the quantum efficiency or quantum yield for the formation (or decomposition) of X is 0x and is defined by... 

The Stark-Einstein law states that one molecule is excited for each quantum or photon of radiation absorbed, consequently, the sum of the primary quantum yields should equal one. This is illustrated by observations of (p for fluorescence (5i So) and intersystem crossing (Si Ti) for some aromatic hydrocarbons in ethanol solution (Table 6.6). ... 

Photolysis rates must be proportional to the total number of photons absorbed per unit time since only one molecule would be activated per photon absorbed according to the Stark-Einstein law. The reaction quantum yield would define the extent to which the activated molecules are transformed. The near-surface (<50 cm) specific rate of iight absorption, in water at a given wavelength is expressed in terms of the solar irradiance, Z(A) (photons cm s or meinsteins cm s ) and the molar extinction coefficient, s(A) ... 

When a molecule or ion absorbs a photon, that photon s energy can be dissipated in several different ways, but one way is for that energy to cause a chemical reaction to occur. The first law of photochemistry is that a compound must absorb light for a photochemical reaction to occur (Grotthuss-Draper law). The second law of photochemistry is that each photon that is absorbed activates only one molecule for a subsequent reaction (Stark-Einstein law). The quantum yield ( ) is defined as the number of molecules that react divided by the number of photons absorbed. It can also be defined in terms of moles. 

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 generalizations about photochemical reactions emerged in the 1950s are perhaps too narrow. The key photochemical steps, as shown in Sect. 7.3, involve absorption of one photon (according to the Stark-Einstein law, 10 -10 s ), internal conversion, and/or intersystem crossing down to the lowest excited singlet or the lowest triplet (Kasha-Vavilov rule, or ki c up to 10 s ) and emission or... 

According to the Stark-Einstein law, should be equal to unity or less. However, if secondary processes occur, (j) can sometime be greater than 1. Under continuous illumination, a steady-state will be reached, such that the rate of excited-state formation, 7abs> will be equal to the rate of deactivation by all intramolecular processes, Ttotab... 

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