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Encyclopedia > Photochemistry

Photochemistry is the study of the interaction of light and chemicals. Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ...


The first law of photochemistry, known as the Grotthuss-Draper law (for chemists Christian J.D.T. von Grotthuss and John W. Draper), states that light must be absorbed by a chemical substance in order for a photochemical reaction to take place. No absorption, no effect. Christian J.D.T. von Grotthuss is the originator of the first law of photochemistry in 1817. ... John William Draper (1811-1882) developed the proposition in 1842 that only light rays that are absorbed can produce chemical change. ...


For example, green grass is green because chlorophyll (an organometallic complex) absorbs other types of light but reflects green. If you try to grow plants under green light (460nm to 600nm) - they will reflect or transmit it all and not be able to photosynthesise. No photochemical reaction will have occurred. A grassy swamp. ... Chlorophyll is a green photosynthetic pigment found in plants, algae, and cyanobacteria. ... Organometallic have classically been compounds having bonds between one or more metal atoms and one or more carbon atoms of an organyl group. ... Leaf. ...


The second law of photochemistry, the Stark-Einstein law, states that for each photon of light absorbed by a chemical system, only one molecule is activated for photochemical reaction. This is also known as the photoequivalence law and was derived by Albert Einstein at the time when the quantum (photon) theory of light was being developed. Only one excited molecule per photon absorbed. Albert Einstein photographed by Oren J. Turner in 1947. ...


Photochemistry may also be introduced to laymen as a reaction that proceeds with the absorption of light. Normally a reaction (not just a photochemical reaction) occurs when a molecule gains necessary energy to undergo change. A simple example can be the combustion of gasoline (a hydrocarbon)into carbon dioxide and water. This is a chemical reaction where one or more molecules/chemical species are converted into others. For this reaction to take place energy should be supplied. The energy is given in the form of heat or a spark. In case of photochemical reactions light is the energy form. A reaction is the following: In physics, a reaction (physics) is defined by Newtons third law: For every action there is an equal and opposite reaction. The idea that any given force has a pair or opposite force. ... Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer), usually O2, to release heat. ... // Definition In chemistry, a hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). ...


Some common terms that may help you learn more about photochemistry are:


Photons, Absorption and Emission (Electronic transitions), Franck Condon Principle, Energy levels, Singlet and Triplet states, Internal conversion, Intersystem crossing, Sensitization, etc. In physics, the photon (from Greek φοτος, meaning light) is a quantum of the electromagnetic field, for instance light. ... Absorption has a number of meanings: In physics, absorption is a process in which particles of some sort encounter another material and are taken up by or even disappear in it. ... The word emission generally means sending something out. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... In theoretical physics, a singlet usually refers to a one-dimensional representation (e. ... A triplet is a set of three items, and includes in particular: one of three babies in a multiple birth a preparation of opal as a gemstone, with a thin layer of opal backed with a dark material and covered with cap of clear quartz in poetry, a tercet (three... This article is about the nuclear process. ... A photophysical process. ... In neurobiology, sensitization is the progressive amplification of a response following repeated administrations of a stimuli (Bell et al. ...



Photochemists use techniques such as:


The Quantum Yield of a radiation-induced process is the number of times that a defined event (usually a chemical reaction step) occurs per photon absorbed by the system. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Flash photolysis is a pump-probe technique, where you excite with short pulse light sources like flash lamp, lasers of nanosecond, picosecond and femtosecond pulse width. ... Xenon flash lamp being fired. ... Absorption spectroscopy is an analytical tool used by chemists. ...

Chemistry
Analytical chemistry | Organic chemistry | Inorganic chemistry | Physical chemistry | Polymer chemistry | Biochemistry | Materials science | Environmental chemistry | Medicinal chemistry | Pharmacy | Thermochemistry | Electrochemistry | Nuclear chemistry | Computational chemistry | Photochemistry
Periodic table | List of inorganic compounds | List of organic compounds | List of biomolecules

  Results from FactBites:
 
Photochemistry - Wikipedia, the free encyclopedia (351 words)
Photochemistry is the study of the interaction of light and chemicals.
The first law of photochemistry, known as the Grotthuss-Draper law (for chemists Christian J.D.T. von Grotthuss and John W. Draper), states that light must be absorbed by a chemical substance in order for a photochemical reaction to take place.
Photochemistry may also be introduced to laymen as a reaction that proceeds with the absorption of light.
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