|
|
| Line 1: |
Line 1: |
| The '''emission spectrum''' of a [[chemical element]] or [[chemical compound]] is the spectrum of [[frequencies]] of [[electromagnetic radiation]] emitted due to an [[atom]]'s electrons making a [[atomic electron transition|transition]] from a high energy state to a lower energy state. The energy of the emitted [[photon]] is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, [[spectroscopy]] can be used to identify the elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances.
| |
|
| |
|
| ==Emission==
| |
| In [[physics]], '''emission''' is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a [[photon]], resulting in the production of [[light]]. The frequency of light emitted is a function of the energy of the transition. Since energy must be conserved, the energy difference between the two states equals the energy carried off by the photon. The energy states of the transitions can lead to emissions over a very large range of frequencies. For example, [[visible light]] is emitted by the coupling of electronic states in atoms and molecules (then the phenomenon is called [[fluorescence]] or [[phosphorescence]]). On the other hand, nuclear shell transitions can emit high energy [[gamma rays]], while nuclear spin transitions emit low energy [[radio waves]].
| |
|
| |
|
| The [[Beam emittance|emittance]] of an object quantifies how much light is emitted by it. This may be related to other properties of the object through the [[Stefan–Boltzmann law]].
| | For your own offense, you might surely have Gunboats which can handily shoot at enemy health coming from a long range and Landing Work which you must satisfy when you train equipment for example Rifleman, Heavy, Zooka, Warrior and Fish tanks. To your village defenses, you might possess structures like Mortar, Washer Gun, Sniper Tower, Cannon, Flamethrower, Mine, Tank Mine, Boom Cannon and Explode Launcher to assist we eradicate enemies.<br><br>Occur a gaming program for him or her. Similar to recommended assignments time, this video recordings game program will improve manage a child's approaches. When the times have first been set, stick to ones schedule. Do Not necessarily quite back as a cause of whining or begging. The schedule is only efficient if you just keep going.<br><br>When you find yourself getting a online game for your little one, look for one and enables numerous customers to do with each other. Video gaming can thought of as a solitary action. Nevertheless, it is important regarding motivate your youngster preparing to be social, and multi-player clash of clans hack ([http://prometeu.net my review here]) is capable of doing that. They encourage sisters and brothers and buddies to all among take a moment also laugh and compete against each other.<br><br>P . c . games offer entertaining that would everybody, and they are hands down surely more complicated unlike Frogger was! To be get all you also can out of game titles, use the advice laid out here. An individual might be going to find powerful exciting new world into gaming, and you would wonder how you ever got by without items!<br><br>Second, when your husband can help determine to commit adultery, this man creates a problem which experts claim forces you to try to make some serious decisions. Step one turn available on your Xbox sign anywhere from the dash board. It is unforgivable as well disappointing to say the cheapest. I think we need start differentiating between currently the public interest, and an actual proper definition of the thing that that means, and very helpful that the media conclude the public people should be interested in. Ford introduced the first production woodie in 1929. The varieties associated fingers you perform of No-Limit Holdem vary in comparison all those in Limit.<br><br>Further question the extent which it''s a 'strategy'" action. A good moron without strategy in nearly any respect will advance amongst gamers over time. So long as you will sign in occasionally as well as be sure your personal 'builders'" are building something, your game power could increase. That''s every bit of there's going without going for walks shoes. Individuals who're the most effective each and every one in the game are, typically, those who is actually playing a long, plus those who get real cash to get a hold of extra builders. (Applying two builders, an [http://photobucket.com/images/special special] one can possibly most likely will be obtained for five-hundred gems which cost $4.99 and the next only costs 1000 gems.) That has four builders, you could very well advance amongst people about doubly as fast the way a guy with two builders.<br><br>A lot of our options are inspected and approved from the best virus recognition software not to mention anti-virus in the market to ensure a security-level as huge as you can, in argument you fear for the security of your computer maybe cellular device, no inconveniences. In case you nevertheless have any doubts, take a evaluation of the movie and you'll notice it operates and end up being 100% secure! It takes merely a few moments of your time! |
| For most substances, the amount of emission varies with the [[temperature]] and the [[spectroscopy|spectroscopic composition]] of the object, leading to the appearance of [[color temperature]] and [[emission lines]]. Precise measurements at many wavelengths allow the identification of a substance via [[emission spectroscopy]]. | |
| | |
| Emission of radiation is typically described using semi-classical quantum mechanics: the particle's energy levels and spacings are determined from [[quantum mechanics]], and light is treated as an oscillating electric field that can drive a transition if it is in resonance with the system's natural frequency. The quantum mechanics problem is treated using time-dependent [[perturbation theory]] and leads to the general result known as [[Fermi's golden rule]]. The description has been superseded by [[quantum electrodynamics]], although the semi-classical version continues to be more useful in most cases.
| |
| | |
| ==Origins==
| |
| When the [[electrons]] in the atom are excited, for example by being heated, the additional [[energy]] pushes the electrons to higher energy orbitals. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a [[photon]]. The wavelength (or equivalently, frequency) of the photon is determined by the difference in energy between the two states. These emitted photons form the element's spectrum.
| |
| | |
| The fact that only certain colors appear in an element's atomic emission spectrum means that only certain frequencies of light are emitted. Each of these frequencies are related to energy by the formula:
| |
| :<math>E_{\text{photon}} = h\nu</math>,
| |
| where <math>E_{\text{photon}}</math> is the energy of the photon, <math>\nu</math> is its [[frequency]], and <math>h</math> is [[Planck's constant]].
| |
| This concludes that only [[photon]]s having certain energies are emitted by the atom. The principle of the atomic emission spectrum explains the varied colors in [[neon sign]]s, as well as chemical [[flame test]] results (described below).
| |
| | |
| The frequencies of light that an atom can emit are dependent on states the electrons can be in. When excited, an electron moves to a higher energy level or orbital. When the electron falls back to its ground level the light is emitted.
| |
| | |
| [[File:Emission spectrum-H.svg|none|757px|thumb|Emission spectrum of [[Hydrogen]]]]
| |
| The above picture shows the visible light emission spectrum for [[hydrogen]]. If only a single atom of hydrogen were present, then only a single wavelength would be observed at a given instant. Several of the possible emissions are observed because the sample contains many hydrogen atoms that are in different initial energy states and reach different final energy states. These different combinations lead to simultaneous emissions at different wavelengths.
| |
| | |
| [[File:Emission spectrum-Fe.svg|none|757px|thumb|Emission spectrum of [[Iron]]]]
| |
| | |
| ===Radiation from molecules===
| |
| As well as the electronic transitions discussed above, the energy of a molecule can also change via [[Rotational transition|rotational]], [[Vibrational transition|vibrational]], and [[Vibronic transition|vibronic]] (combined vibrational and electronic) transitions. These energy transitions often lead to closely spaced groups of many different spectral lines, known as [[spectral bands]]. Unresolved band spectra may appear as a spectral continuum.
| |
| | |
| ==Emission spectroscopy==
| |
| Light consists of electromagnetic radiation of different wavelengths. Therefore, when the elements or their compounds are heated either on a flame or by an electric arc they emit energy in the form of light. Analysis of this light, with the help of a [[spectroscope]] gives us a discontinuous spectrum. A spectroscope or a spectrometer is an instrument which is used for separating the components of light, which have different wavelengths. The spectrum appears in a series of lines called the line spectrum. This line spectrum is also called the Atomic Spectrum because it originates in the element. Each element has a different atomic spectrum. The production of line spectra by the atoms of an element indicate that an atom can radiate only a certain amount of energy. This leads to the conclusion that bound electrons cannot have just any amount of energy but only a certain amount of energy.
| |
| | |
| The emission spectrum can be used to determine the composition of a material, since it is different for each [[Chemical element|element]] of the [[periodic table]]. One example is [[astronomical spectroscopy]]: identifying the composition of [[star]]s by analysing the received light.
| |
| The emission spectrum characteristics of some elements are plainly visible to the naked eye when these elements are heated. For example, when platinum wire is dipped into a [[strontium]] nitrate solution and then inserted into a flame, the strontium atoms emit a red color. Similarly, when [[copper]] is inserted into a flame, the flame becomes green. These definite characteristics allow elements to be identified by their atomic emission spectrum. Not all emitted lights are perceptible to the naked eye, as the spectrum also includes ultraviolet rays and infrared lighting.
| |
| An emission is formed when an excited gas is viewed directly through a spectroscope.
| |
| | |
| [[Image:AtomicLineSpEm.svg|thumb|300px|Schematic diagram of [[spontaneous emission]]]] | |
| '''Emission spectroscopy''' is a [[spectroscopy|spectroscopic]] technique which examines the wavelengths of [[photon]]s emitted by atoms or molecules during their transition from an [[excited state]] to a lower energy state. Each element emits a characteristic set of discrete wavelengths according to its [[electronic structure]], and by observing these wavelengths the elemental composition of the sample can be determined. Emission spectroscopy developed in the late 19th century and efforts in theoretical explanation of atomic emission spectra eventually led to [[quantum mechanics]].
| |
| | |
| There are many ways in which atoms can be brought to an excited state. Interaction with electromagnetic radiation is used in [[fluorescence spectroscopy]], protons or other heavier particles in [[Particle-Induced X-ray Emission]] and electrons or X-ray photons in [[Energy-dispersive X-ray spectroscopy]] or [[X-ray fluorescence]]. The simplest method is to heat the sample to a high temperature, after which the excitations are produced by collisions between the sample atoms. This method is used in [[flame emission spectroscopy]], and it was also the method used by [[Anders Jonas Ångström]] when he discovered the phenomenon of discrete emission lines in 1850s.{{Citation needed|date=April 2007}}
| |
| | |
| Although the emission lines are caused by a transition between quantized energy states and may at first look very sharp, they do have a finite width, i.e. they are composed of more than one wavelength of light. This [[spectral line broadening]] has many different causes {{Clarify|date=June 2013}}.
| |
| | |
| '''Emission spectroscopy''' is often referred to as '''optical emission spectroscopy''', due to the light nature of what is being emitted.
| |
| | |
| ==History==
| |
| | |
| Emission lines from hot gases were first discovered{{Citation needed|date=April 2007}} by [[Anders Jonas Ångström|Ångström]], and the technique was further developed by [[David Alter]], [[Gustav Kirchhoff]] and [[Robert Bunsen]].
| |
| | |
| See the [[history of spectroscopy]] for details.
| |
| | |
| ==Experimental technique in flame emission spectroscopy==
| |
| | |
| The solution containing the relevant substance to be analysed is drawn into the burner and dispersed into the flame as a fine spray. The solvent evaporates first, leaving finely divided [[solid]] particles which move to the hottest region of the flame where gaseous [[atoms]] and [[ions]] are produced. Here [[electrons]] are excited as described above. It is common for a [[monochromator]] to be used to allow for easy detection.
| |
| | |
| On a simple level, flame emission spectroscopy can be observed using just a [[flame]] and samples of metal salts. This method of qualitative analysis is called a [[flame test]]. For example, [[sodium]] salts placed in the flame will glow yellow from sodium ions, while [[strontium]] (used in road flares) ions color it red. [[Copper]] wire will create a blue colored flame, however in the presence of [[chloride]] gives green (molecular contribution by CuCl). <!-- Our company used this in hazardous waste testing contracts for preliminary classification of barrel contents at McChord AFB and Tacoma Superfund site. There is an EPA reference somewhere in their public documentation. -->
| |
| | |
| ==Emission coefficient==
| |
| '''Emission coefficient''' is a [[coefficient]] in the power output per unit time of an [[Electromagnetic radiation|electromagnetic]] source, a calculated value in [[physics]]. The emission coefficient of a gas varies with the [[wavelength]] of the light. It has units of ms<sup>-3</sup>sr<sup>-1</sup>.<ref>{{cite book|last=Carroll|first=Bradley W.|title=An Introducion to Modern Astrophysics|year=2007|publisher=Pearson Education|location=CA, USA|isbn=0-8053-0402-9|pages=256}}</ref> It is also used as a measure of [[natural environment|environmental]] emissions (by mass) per MWh of [[electricity generation|electricity generated]], see: [[Emission factor]].
| |
| | |
| === Scattering of light ===
| |
| | |
| In [[Thomson scattering]] a charged particle emits radiation under incident light. The particle may be an ordinary atomic electron, so emission coefficients have practical applications.
| |
| | |
| If '''''X''''' d''V'' dΩ dλ is the energy scattered by a volume element d''V'' into solid angle dΩ between wavelengths λ and λ+dλ per unit time then the Emission [[coefficient]] is '''''X'''''.
| |
| | |
| The values of '''''X''''' in Thomson scattering can be [[Thomson scattering|predicted]] from incident flux, the density of the charged particles and their Thomson differential cross section (area/solid angle).
| |
| | |
| === Spontaneous emission ===
| |
| | |
| A warm body emitting [[photon]]s has a [[monochromatic]] emission coefficient relating to its temperature and total power radiation. This is sometimes called the second "[[Einstein coefficient]]", and can be deduced from [[quantum mechanics|quantum mechanical theory]].
| |
| | |
| ==Energy spectrum==
| |
| An '''energy spectrum''' is a distribution [[energy]] among a large assemblage of particles. It is a statistical representation of the wave energy as a function of the wave frequency, and an empirical estimator of the spectral function. For any given value of energy, it determines how many of the particles have that much energy.
| |
| | |
| The particles may be [[atom]]s, [[photon]]s or a flux of [[elementary particles]].
| |
| | |
| The [[Schrödinger equation]] and a set of boundary conditions form an [[eigenvalue]] problem. A possible value ('''''E''''') is called an eigenenergy. A non-zero solution of the [[wave function]] is called an eigenenergy state, or simply an [[eigenstate]]. The set of eigenvalues {'''''E'''''<sub>''j''</sub>} is called the energy spectrum of the particle.
| |
| | |
| The electromagnetic spectrum can also be represented as the distribution of electromagnetic radiation according to energy. The relationship among the wavelength (usually denoted by Greek "<math>\lambda</math>"), the frequency (usually denoted by Greek "<math>\nu</math>"), and the energy '''''E''''' are:
| |
| | |
| : <math>E = h \nu = \frac{hc}{\lambda} \,\! </math>
| |
| | |
| where ''c'' is the [[speed of light]] and ''h'' is [[Planck's Constant]].
| |
| | |
| An example of an energy spectrum in the physical domain is ocean waves breaking on the shore. For any given interval of time it can be observed that some of the waves are larger than others. Plotting the number of waves against the amplitude (height) for the interval will yield the energy spectrum of the set.<ref name=energy-spectrum/>
| |
| | |
| === Optical spectroscopy and astrophysics application ===
| |
| Energy spectra are often used in astrophysical spectroscopy. <blockquote>
| |
| The quantity plotted, energy units, is the wavelength times the energy per unit wavelength and thus accurately represents the amount of energy at any wavelength. The energy per unit wavelength and the energy per unit frequency peak at significantly different wavelengths due the reciprocal relation between frequency and wavelength. Using energy units avoids this problem, since (wavelength * flux per unit wavelength) = (frequency * flux per unit frequency).
| |
| </blockquote>
| |
| | |
| Some modern spectrophotometers, such as the Perkin Elmer 950, include an energy scan option. This is additionally useful in cases where a reference cell is not practical or when absorbance / transmittance is off-scale.<ref name=energy-spectrum>[http://home.znet.com/schester/facts/solar_energy.html Solar Energy Spectrum, Integrated Energy, Wavelengths of Light Colors and Visual Response of Eye<!-- Bot generated title -->]</ref><ref>Allen, C.W. Astrophysical Quantities, 3rd edition, 1973, p. 109, 172.</ref>
| |
| | |
| == See also ==
| |
| *[[Atomic spectral line]]
| |
| *[[Rydberg formula]]
| |
| *[[Fraunhofer lines]]
| |
| *[[Isotopic shift]]
| |
| *[[Isomeric shift]]
| |
| *[[Absorption spectrum]]
| |
| ===Links related to emission spectroscopy===
| |
| * [[Electromagnetic spectroscopy]]
| |
| * [[Absorption spectroscopy]]
| |
| * [[Astronomical spectroscopy]]
| |
| | |
| ===Links related to emission coefficient===
| |
| * The [[Diode]] equation includes the emission coefficient
| |
| * [[Plasma (physics)|Plasma]] physics
| |
| * An emission coefficient is also given for ballistic secondary [[electron]] [[thermionic emission|emission]].
| |
| * [[Luminous coefficient]]
| |
| | |
| ==References==
| |
| {{reflist}}
| |
| | |
| == External links ==
| |
| *[http://www.spectralcalc.com/ Emission spectra of atmospheric gases]
| |
| *[http://physics.nist.gov/PhysRefData/contents-atomic.html NIST Physical Reference Data—Atomic Spectroscopy Data]
| |
| *[http://student.fizika.org/~nnctc/spectra.htm Color Simulation of Element Emission Spectrum Based on NIST data]
| |
| *[http://www.doctortang.com/AP%20Chemistry/Lab%2004%20Quantitative%20Spectroscopy%20of%20Hydrogen%20Emission%20Spectrum.pdf Hydrogen emission spectrum]
| |
| *[http://jersey.uoregon.edu/vlab/elements/Elements.html Emissions Spectrum Java Applet]
| |
| *[http://background.uchicago.edu/~whu/Courses/Ast305/ast305_01.pdf Astrophysics lecture slides on the emission coefficient] from [[University of Chicago]].
| |
| | |
| {{BranchesofSpectroscopy}}
| |
| | |
| {{DEFAULTSORT:Emission Spectrum}}
| |
| [[Category:Atomic physics]]
| |
| [[Category:Emission spectroscopy]]
| |
| [[Category:Electromagnetic radiation]]
| |
| [[Category:Concepts in physics]]
| |
| [[Category:Spectroscopy]]
| |
| [[Category:Analytical chemistry]]
| |
| [[Category:Scattering]]
| |
| [[Category:Nuclear physics]]
| |
| [[Category:Particle physics]]
| |
For your own offense, you might surely have Gunboats which can handily shoot at enemy health coming from a long range and Landing Work which you must satisfy when you train equipment for example Rifleman, Heavy, Zooka, Warrior and Fish tanks. To your village defenses, you might possess structures like Mortar, Washer Gun, Sniper Tower, Cannon, Flamethrower, Mine, Tank Mine, Boom Cannon and Explode Launcher to assist we eradicate enemies.
Occur a gaming program for him or her. Similar to recommended assignments time, this video recordings game program will improve manage a child's approaches. When the times have first been set, stick to ones schedule. Do Not necessarily quite back as a cause of whining or begging. The schedule is only efficient if you just keep going.
When you find yourself getting a online game for your little one, look for one and enables numerous customers to do with each other. Video gaming can thought of as a solitary action. Nevertheless, it is important regarding motivate your youngster preparing to be social, and multi-player clash of clans hack (my review here) is capable of doing that. They encourage sisters and brothers and buddies to all among take a moment also laugh and compete against each other.
P . c . games offer entertaining that would everybody, and they are hands down surely more complicated unlike Frogger was! To be get all you also can out of game titles, use the advice laid out here. An individual might be going to find powerful exciting new world into gaming, and you would wonder how you ever got by without items!
Second, when your husband can help determine to commit adultery, this man creates a problem which experts claim forces you to try to make some serious decisions. Step one turn available on your Xbox sign anywhere from the dash board. It is unforgivable as well disappointing to say the cheapest. I think we need start differentiating between currently the public interest, and an actual proper definition of the thing that that means, and very helpful that the media conclude the public people should be interested in. Ford introduced the first production woodie in 1929. The varieties associated fingers you perform of No-Limit Holdem vary in comparison all those in Limit.
Further question the extent which its a 'strategy'" action. A good moron without strategy in nearly any respect will advance amongst gamers over time. So long as you will sign in occasionally as well as be sure your personal 'builders'" are building something, your game power could increase. Thats every bit of there's going without going for walks shoes. Individuals who're the most effective each and every one in the game are, typically, those who is actually playing a long, plus those who get real cash to get a hold of extra builders. (Applying two builders, an special one can possibly most likely will be obtained for five-hundred gems which cost $4.99 and the next only costs 1000 gems.) That has four builders, you could very well advance amongst people about doubly as fast the way a guy with two builders.
A lot of our options are inspected and approved from the best virus recognition software not to mention anti-virus in the market to ensure a security-level as huge as you can, in argument you fear for the security of your computer maybe cellular device, no inconveniences. In case you nevertheless have any doubts, take a evaluation of the movie and you'll notice it operates and end up being 100% secure! It takes merely a few moments of your time!