Excited state: Difference between revisions
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[[Image:Energylevels.png|thumb|right| After absorbing energy, an electron may jump from the ground state to a higher energy excited state.]] |
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'''Excitation''' is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for [[energy level]] which is often associated with an atom being excited to an excited state. |
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In [[quantum mechanics]] an '''excited state''' of a system (such as an [[atom]], [[molecule]] or [[Atomic nucleus|nucleus]]) is any [[quantum state]] of the system that has a higher [[energy]] than the [[ground state]] (that is, more energy than the absolute minimum). |
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The [[temperature]] of a group of particles is indicative of the level of excitation. |
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The lifetime of a system in an excited state is usually short: [[Spontaneous emission|spontaneous]] or [[stimulated emission|induced emission]] of a quantum of energy (such as a [[photon]] or a [[phonon]]) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state). This return to a lower energy level is often loosely described as decay and is the inverse of excitation. |
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Long-lived excited states are often called [[metastable]]. Long-lived [[nuclear isomer]]s and [[singlet oxygen]] are two examples of this. |
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==Atomic excitation== |
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A simple example of this concept comes by considering the [[hydrogen atom]]. |
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The ground state of the hydrogen atom corresponds to having the atom's single [[electron]] in the lowest possible [[atomic orbital|orbit]] (that is, the spherically symmetric "1s" [[wavefunction]], which has the lowest possible [[quantum number]]s). By giving the atom additional energy (for example, by the absorption of a [[photon]] of an appropriate energy), the electron is able to move into an excited state (one with one or more quantum numbers greater than the minimum possible). If the photon has too much energy, the electron will cease to be [[bound state|bound]] to the atom, and the atom will become [[ion]]ised. |
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After excitation the atom may return to a lower excited state, or the ground state, by emitting a photon with a characteristic energy. Emission of photons from atoms in various excited states leads to an [[electromagnetic spectrum]] showing a series of characteristic [[emission line]]s (including, in the case of the hydrogen atom, the [[Hydrogen spectral series|Lyman, Balmer, Paschen and Brackett series]].) |
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An atom in a high excited state is termed [[Rydberg atom]]. A system of highly excited atoms can form a long-lived condensed excited state e.g. a condensed phase made completely of excited atoms: [[Rydberg matter]]. Hydrogen can also be excited by heat or electricity. |
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==Perturbed gas excitation== |
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A collection of molecules forming a gas can be considered in an excited state if one or more molecules are elevated to kinetic energy levels such that the resulting velocity distribution departs from the equilibrium [[Maxwell-Boltzmann statistics|Maxwell-Boltzmann]] distribution. This phenomenon has been studied in the case of a [[two-dimensional gas]] in some detail, analyzing the time taken to relax to equilibrium. |
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==See also== |
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*[[Rydberg formula]] |
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*[[Stationary state]] |
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==External links== |
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* [http://www.klimaforschung.net/kernreaktion/Orbital01.gif Picture of a hydrogen atom changing from ground state to an excited state] |
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* [http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-atoms.html NASA background information on ground and excited states] |
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[[Category:Quantum mechanics]] |
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[[cs:Excitovaný stav]] |
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[[de:Angeregter Zustand]] |
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[[et:Ergastatud olek]] |
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[[fa:حالت برانگیخته]] |
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[[fr:Excitation (physique)]] |
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[[it:Eccitazione]] |
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[[he:עירור]] |
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[[lt:Sužadinta būsena]] |
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[[nl:Aangeslagen toestand]] |
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[[ja:励起状態]] |
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[[sk:Excitácia (zvýšenie energie)]] |
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[[sl:Vzbujeno stanje]] |
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[[fi:Viritystila]] |
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[[sv:Excitation]] |
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[[uk:Збуджений стан квантовомеханічної системи]] |
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Revision as of 21:00, 9 December 2009
Deleted for relevance