What is Lyman alpha: Definition and 11 Discussions

In physics, the Lyman-alpha line, sometimes written as Ly-α line, is a spectral line of hydrogen, or more generally of one-electron ions, in the Lyman series, emitted when the electron falls from the n = 2 orbital to the n = 1 orbital, where n is the principal quantum number. In hydrogen, its wavelength of 1215.67 angstroms (121.567 nm or 1.21567×10−7 m), corresponding to a frequency of 2.47×1015 hertz, places the Lyman-alpha line in the vacuum ultraviolet part of the electromagnetic spectrum, which is absorbed by air. Lyman-alpha astronomy must therefore ordinarily be carried out by satellite-borne instruments, except for extremely distant sources whose redshifts allow the hydrogen line to penetrate the atmosphere.
Because of fine structure perturbations, the Lyman-alpha line splits into a doublet with wavelengths 1215.668 and 1215.674 angstroms. Specifically, because of the electron's spin-orbit interaction, the stationary eigenstates of the perturbed Hamiltonian must be labeled by the total angular momentum j of the electron (spin plus orbital), not just the orbital angular momentum l. In the n = 2 orbital, there are two possible states, j = 1/2 and j = 3/2, resulting in a spectral doublet. The j = 3/2 state is of higher energy (less negative) and so is energetically farther from the n = 1 orbital to which it is transitioning. Thus, the j = 3/2 state is associated with the more energetic (shorter wavelength) spectral line in the doublet.The less energetic spectral line has been measured at 2466061413187035(10) Hz, or 1215.673123130217(5) Å. The line has also been measured in antihydrogen.A K-alpha line, or Kα, analogous to the Lyman-alpha line for hydrogen, occurs in the high-energy induced emission spectra of all chemical elements, since it results from the same electron transition as in hydrogen. The equation for the frequency of this line (usually in the X-ray range for heavier elements) uses the same base-frequency as Lyman-alpha, but multiplied by a (Z − 1)2 factor to account for the differing atomic numbers (Z) of heavier elements, as approximated by Moseley's law.The Lyman-alpha line is most simply described by the {n,m} = {1,2...} solutions to the empirical Rydberg formula for hydrogen's Lyman spectral series. (The Lyman-alpha frequency is produced by multiplying the Rydberg frequency for the atomic mass of hydrogen, RM (see Rydberg constant), by a factor of (1/1)2 − (1/2)2 = 3/4.) Empirically, the Rydberg equation is in turn modeled by the semi-classical Bohr model of the atom.

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  1. neilparker62

    Insights Revisiting The Deuterium Lyman Alpha Line Experiment

    [url="https://www.physicsforums.com/insights/the-deuterium-lyman-alpha-line/"]Continue reading...
  2. F

    I Understanding Gunn-Peterson through the Reionization epoch

    Into an extra-galactic physics course, I don't understand well the "Gunn - Peterson" effect on the spectrum of high redshift quasars (z greater than 3 or 4, up to the current limit of z = 6-7 I think) The observed fact is that there is an almost total absorption for the photons of the blue part...
  3. E

    I Understanding the Ly-α Forest for EnSlavingBlair

    Hi, I'm currently trying to wrap my head around how the Ly-α forest works. This is what I have so far; A distant quasar produces these Ly-α photons, which occur when a hydrogen's electron drops from n=2 to n=1, and has a wavelength of around 121nm (depending on the exact transition). This...
  4. A

    A Lyman-alpha forest: why not Lyman-beta?

    Hello everyone! We observe the so-called Lyman-alpha forest in the spectrum of distant quasars and it is said that these multiple absorption lines are due to the presence of intergalactic HI clouds that absorb light at the wavelenght of 1216 A , the Lyman-alpha transition. My question is the...
  5. M

    I Hydrogen Atom Photon Emission Wavelength Formula

    I am trying to calculate the Lyman-alpha wavelengths of photons emitted from different hydrogen-like atoms such as deuterium and positive helium ion 4He+, using the relation 1/λ = R*|1/ni^2 - 1/nf^2|, where R is the Rydberg constant and ni and nf are integer numbers corresponding to the initial...
  6. J

    Copper K alpha lines, ionization potential, confused

    I'm a computer scientist who was recently given a book about quantum physics. I am confused about something in the book. Imagine shining an x-ray (produced by copper K alpha 1 emission) on an aluminium foil. I understand the basics of photoelectric effect. You shine the x-ray on target aluminium...
  7. G

    Recoil of a hydrogen atom emitting Lyman alpha photon

    I am interested in what the recoil velocity of an initially stationary hydrogen atom in free space would be when it emits a Lyman alpha photon. I tried to do the calc and got about 3 metres per second which seems rather high.
  8. F

    Rate of Lyman Alpha photons emitted....

    First off, I'm not sure if this question should go here or in the homework section. It is an astronomy homework question BUT there are only physics subtopics and did not want to post it in the wrong section. Let me know if it should be moved to there! Homework Statement Consider a nebula...
  9. neilparker62

    Questions on the Lyman Alpha Profile

    A few questions about the solar Lyman Alpha profile as presented here. 1) This is from a 1978 study - are there more recent (higher resolution) profiles ? 2) The scale at the bottom is confusing - how does it relate to a wavelength scale ? 3) Where in the profile is the actual Lyman alpha line...
  10. Jonathan Scott

    Lyman alpha forest different for different objects?

    I was wondering how the distribution of Lyman alpha absorbers (as seen in the "forest" of absorption lines of a quasar spectrum) varies with red-shift (corresponding to evolution with the age of the universe). I've found various sources which mention in passing that the frequency of absorbers...
  11. D

    K3 in space as a Lyman alpha blob?

    Space.com 27 July 2006 discusses 'Newfound Blob is Biggest Thing in the Universe' as: "... The galaxies and gas bubbles, called Lyman alpha blobs, are aligned along three curvy filaments that formed about 2 billion years after the universe exploded into existence after the theoretical Big Bang...