- Balmer series
The

**Balmer series**or**Balmer lines**inatomic physics , is the designation of one of a set of six different named series describing thespectral line emissions of thehydrogen atom .The Balmer series is calculated using the

**Balmer formula**, anempirical equation discovered byJohann Balmer in 1885. The visiblespectrum oflight fromhydrogen displays fourwavelength s, 410 nm, 434 nm, 486 nm, and 656 nm, that reflect emissions ofphoton s byelectron s in excited states transitioning to the quantum level described by theprincipal quantum number "n" equals 2. [*C.R. Nave (2006). HyperPhysics: [*]*http://hyperphysics.phy-astr.gsu.edu/Hbase/hyde.html#c4 "Hydrogen Spectrum"*] . Georgia State University. Accessed March 1st, 2008.**Overview**The Balmer series is characterized by the

electron transitioning from "n" ≥ 3 to "n" = 2, where "n" refers to theradial quantum number orprincipal quantum number of the electron. The transitions are named sequentially by Greek letter: "n" = 3 to "n" = 2 is called H-α, 4 to 2 is H-β, 5 to 2 is H-γ, and 6 to 2 is H-δ. As the first spectral lines associated with this series are located in the visible part of theelectromagnetic spectrum , these lines are historically referred to as "H-alpha", "H-beta", "H-gamma" and so on, where H is the element hydrogen.Although physicists were aware of atomic emissions before 1885, they lacked a tool to accurately predict where the spectral lines should appear. The Balmer equation predicts the four visible absorption/emission lines of hydrogen with high accuracy. Balmer's equation inspired the

Rydberg equation as a generalization of it, and this in turn led physicists to find the Lyman, Paschen, andBrackett series which predicted other absorption/emission lines of hydrogen found outside thevisible spectrum .The familiar red

H-alpha spectral line of hydrogen gas, which is the transition from the shell "n" = 3 to the Balmer series shell "n" = 2, is one of the conspicuous colors of the universe. It contributes a bright red line to the spectra of emission or ionization nebula, like theOrion Nebula , which are oftenH II regions found in star forming regions. In true-color pictures, these nebula have a distinctly pink color from the combination of visible Balmer lines that hydrogen emits.Later, it was discovered that when the spectral lines of the hydrogen spectrum are examined at very high resolution, they are found to be closely-spaced doublets. This splitting is called

fine structure . It was also found that excited electrons could jump to the Balmer series "n"=2 from orbitals where "n" was greater than 6, emitting shades of violet when doing so.**Balmer's formula**Balmer noticed that a single number had a relation to every line in the hydrogen spectrum that was in the

visible light region. That number was 364.56 nm. When any integer higher than 2 was squared and then divided by itself minus 4, then that number multiplied by 364.56 gave a wavelength of another line in the visible hydrogen spectrum. By this formula he was able to show that certain measurements of lines made in his time byspectroscopy were slightly inaccurate measurements and his formula predicted lines that were later found although had not yet been observed. His number also proved to be the limit of the series.The Balmer equation could be used to find the

wavelength of the absorption/emission lines and was originally presented as follows (save for a notation change to give Balmer's constant as "B")::$lambda\; =\; Bleft(frac\{m^2\}\{m^2\; -\; n^2\}\; ight)\; =\; Bleft(frac\{m^2\}\{m^2\; -\; 2^2\}\; ight)$

Where:$lambda$ is the wavelength.:"B" is a constant with the value of 3.6456×10

^{-7}m or 364.56 nm.:"n" is equal to 2:"m" is an integer such that "m" > "n".In

1888 the physicistJohannes Rydberg generalized the Balmer equation for all transitions of hydrogen. The equation commonly used to calculate the Balmer series is a specific example of theRydberg formula and follows as a simple reciprocal mathematical rearrangement of the formula above (conventionally using a notation of**n**for**m**as the single integral constant needed)::$frac\{1\}\{lambda\}\; =\; frac\{4\}\{B\}left(frac\{1\}\{2^2\}\; -\; frac\{1\}\{n^2\}\; ight)\; =\; R\_mathrm\{H\}left(frac\{1\}\{2^2\}\; -\; frac\{1\}\{n^2\}\; ight),\; n=3,4,5,...$

where λ is the wavelength of the absorbed/emitted light and "R"

_{H}is theRydberg constant for hydrogen. The Rydberg constant is seen to be equal to 4/B in Balmer's formula, and for an infinitely heavy nucleus is 4/(3.6456*10^{-7}m) = 10,973,731.57 m^{−1}.cite web |url=http://physics.nist.gov/cuu/Constants/codata.pdf |title=CODATA Recommended Values of the Fundamental Physical Constants: 2006 |work=Committee on Data for Science and Technology (CODATA) |publisher=NIST |format=PDF]**Role in astronomy**The Balmer series is particularly useful in

astronomy because the Balmer lines appear in numerous stellar objects due to the abundance of hydrogen in theuniverse , and therefore are commonly seen and relatively strong compared to lines from other elements.The spectral classification of stars, which is primarily a determination of surface temperature, is based on the relative strength of spectral lines, and the Balmer series in particular are very important. Other characteristics of a star can be determined by close analysis of its spectrum include

surface gravity (related to physical size) and composition.Because the Balmer lines are commonly seen in the spectra of various objects, they are often used to determine radial velocities due to

doppler shift ing of the Balmer lines. This has important uses all over astronomy, from detectingbinary star s,exoplanet s, compact objects such asneutron star s andblack hole s (by the motion of hydrogen inaccretion disk s around them), identifying groups of objects with similar motions and presumably origins (moving group s,star cluster s,galaxy cluster s, and debris from collisions), determining distances (actuallyredshift s) of galaxies orquasar s, and identifying unfamiliar objects by analysis of their spectrum.Balmer lines can appear as absorption or emission lines in a spectrum, depending on the nature of the object observed. In

star s, the Balmer lines are usually seen in absorption, and they are "strongest" in stars with a surface temperature of about 10,000kelvin (spectral type A). In the spectra of most spiral and irregular galaxies, AGNs,H II region s and planetarynebula e, the Balmer lines are emission lines.In stellar spectra, the H-epsilon line (transition 7-2) is often mixed in with another absorption line caused by ionized

calcium known by astronomers as "H" (the original designation given by Fraunhofer). That is, H-epsilon's wavelength is quite close to CaH at 396.847nm, and cannot be resolved in low resolution spectra. The H-zeta line (transition 8-2) is similarly mixed in with a neutralhelium line seen in hot stars.**ee also***

Astronomical spectroscopy

*Stellar classification

*Bohr model

*Theoretical and experimental justification for the Schrödinger equation

*H-alpha

*Rydberg formula

*Balmer's Constant **Notes****External links*** [

*http://www.bigs.de/en/shop/htm/termsch01.html Balmer series (animation)*]

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