Lyman series
In
History
The first line in the spectrum of the Lyman series was discovered in 1906 by physicist Theodore Lyman, who was studying the ultraviolet spectrum of electrically excited hydrogen gas. The rest of the lines of the spectrum (all in the ultraviolet) were discovered by Lyman from 1906-1914. The spectrum of radiation emitted by hydrogen is non-continuous or discrete. Here is an illustration of the first series of hydrogen emission lines:
Historically, explaining the nature of the hydrogen spectrum was a considerable problem in
On December 1, 2011, it was announced that Voyager 1 detected the first Lyman-alpha radiation originating from the Milky Way galaxy. Lyman-alpha radiation had previously been detected from other galaxies, but due to interference from the Sun, the radiation from the Milky Way was not detectable.[1]
The Lyman series
The version of the Rydberg formula that generated the Lyman series was:[2]
Therefore, the lines seen in the image above are the wavelengths corresponding to n = 2 on the right, to n = ∞ on the left. There are infinitely many spectral lines, but they become very dense as they approach n = ∞ (the Lyman limit), so only some of the first lines and the last one appear.
The wavelengths in the Lyman series are all ultraviolet:
n | Wavelength (nm) |
---|---|
2 | 121.56701[3] |
3 | 102.57220[3] |
4 | 97.253650[3] |
5 | 94.974287[3] |
6 | 93.780331[3] |
7 | 93.0748142[3] |
8 | 92.6225605[3] |
9 | 92.3150275[3] |
10 | 92.0963006[3] |
11 | 91.9351334[3] |
∞, the Lyman limit | 91.1753 |
Explanation and derivation
In 1914, when Niels Bohr produced his Bohr model theory, the reason why hydrogen spectral lines fit Rydberg's formula was explained. Bohr found that the electron bound to the hydrogen atom must have quantized energy levels described by the following formula,
According to Bohr's third assumption, whenever an electron falls from an initial energy level Ei to a final energy level Ef, the atom must emit radiation with a wavelength of
There is also a more comfortable notation when dealing with energy in units of electronvolts and wavelengths in units of angstroms,
- Å.
Replacing the energy in the above formula with the expression for the energy in the hydrogen atom where the initial energy corresponds to energy level n and the final energy corresponds to energy level m,
Where RH is the same Rydberg constant for hydrogen from Rydberg's long known formula. This also means that the inverse of the Rydberg constant is equal to the Lyman limit.
For the connection between Bohr, Rydberg, and Lyman, one must replace m with 1 to obtain
which is Rydberg's formula for the Lyman series. Therefore, each wavelength of the emission lines corresponds to an electron dropping from a certain energy level (greater than 1) to the first energy level.
See also
- Bohr model
- H-alpha
- Hydrogen spectral series
- K-alpha
- Lyman-alpha line
- Lyman continuum photon
- Moseley's law
- Rydberg formula
- Balmer series
References
- ^ "Voyager Probes Detect "invisible" Milky Way Glow". National Geographic. December 1, 2011. Archived from the original on December 3, 2011. Retrieved 2013-03-04.
- ISBN 0-471-60531-X.
- ^ a b c d e f g h i j Kramida, A., Ralchenko, Yu., Reader, J., and NIST ASD Team (2019). NIST Atomic Spectra Database (ver. 5.7.1), [Online]. Available: https://physics.nist.gov/asd [2020, April 11]. National Institute of Standards and Technology, Gaithersburg, MD. DOI: https://doi.org/10.18434/T4W30F