Lyman-alpha

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Lyman-alpha line
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Lyman-alpha, typically denoted by Ly-α, is a

air
.

Fine structure

The Lyman-alpha doublet.

Because of the spin–orbit interaction, the Lyman-alpha line splits into a fine-structure doublet with the wavelengths of 1215.668 and 1215.674 angstroms.[1] These components are called Ly-α3/2 and Ly-α1/2, respectively.

The eigenstates of the perturbed Hamiltonian are labeled by the total angular momentum j of the electron, not just the orbital angular momentum l. In the n = 2, l = 1 orbital, there are two possible states, with j = 1/2 and j = 3/2, resulting in a spectral doublet. The j = 3/2 state has a higher energy and so is energetically farther from the n = 1 state to which it is transitioning. Thus, the j = 3/2 state is associated with the more energetic (having a shorter wavelength) spectral line in the doublet.[2]

Observation

Since the hydrogen Lyman-alpha radiation is strongly absorbed by the air, its observation in laboratory requires use of vacuumed spectroscopic systems. For the same reason, Lyman-alpha astronomy is ordinarily carried out by satellite-borne instruments, except for observing extremely distant sources whose redshifts allow the line to penetrate the Earth atmosphere.

The line was also observed in antihydrogen.[3] Within the experimental uncertainties, the measured frequency is equal to that of hydrogen, in agreement with predictions of quantum electrodynamics.

See also

References

  1. ^ Kramida, Alexander; Ralchenko, Yuri (1999), NIST Atomic Spectra Database, NIST Standard Reference Database 78, National Institute of Standards and Technology, retrieved 2021-06-27
  2. OCLC 706016938
    .
  3. .