Lyman-alpha spectral line

1. The Lyman- alpha line By Jayam chemistry learners Blog URL: https://jayamchemistrylearners.blo gspot.com/

2. Introduction:  The Lyman-alpha spectral line results due to electron transition from the first stationary ground level of the atom to its immediate next higher orbicular configuration n=2 in the hydrogen spectrum.  It was named after the Harvard physicist Theodore Lyman. The Greek letter α denotes it, and its symbolization is Ly-α.  The Lyman-alpha spectral line occurs at the longest wavelength of 121.5 nm. And it has the smallest frequency of 2.47X1015Hz.  It lies in the vacuum-ultraviolet region.  It lies in the vacuum-ultraviolet region. It is characterized by a strong absorption in the air. Hence, satellite-borne instruments are used to study the Lyman-alpha astronomy.

3. Lyman series electron transition  The initial principal quantum number n1value for the Lyman series is 1. And the final quantum number n2 shows a wide range variation in values from 2 to ∞ that results in a bunch of spectral lines in the Lyman series.  Comparatively, the discontinuous spectral appearances confirm the existence of quantized electron orbits that accounts for atomic stability.

4. Greek-notation for Lyman series lines The electron oscillation between n=2 to n=1 gives the Lyman-alpha emission, and the electron transference from n=3 to n=1 shows the Lyman-beta line. In the same way, the Lyman-gamma line occurs during the electron transference between n=4 to n=1. The below table shows the Greek-notation of Lyman-alpha transitions that occur in the hydrogen atom. n1value n2value Greek-letter notation Lyman-alpha Lyman-beta Lyman-gamma Symbolization n1= 1 n1= 1 n1= 1 n2=2 n2=3 n2=4 Ly-α Ly-β Ly-γ

5. Scientist life history  The U.S. Physicist and spectroscopist Theodore Lyman IV was born on November 23, 1874, in Massachusetts, Boston.  He completed his Ph.D. from Harvard University in physics and rendered his service as a Physics professor at Harvard University.  He researched light radiations of shorter wavelengths, particularly ultraviolet radiations and their properties. It made him discover the first line in the ultraviolet region of the Lyman series in 1906.  By extending his hydrogen spectrum studies, he found the rest of the lines in the Lyman series from 1906 to 1914.

6. Energy calculation for Lyman-alpha line The hydrogen electron has -13.6 eV energy in the first stationary orbit. When it is in the second orbit, its energy 10.2 eV is -3.4 eV. So, the difference in energy between the first and second static levels of the hydrogen atom is 10.2 eV. Therefore, the Lyman-alpha transition requires 10.2 eV n=1 energy to occur. n=2 ΔE= energy difference between the two electron transition states E1 = Energy of the first main level E2 = Energy of the second main level

7. Wavelength calculation for Lyman-alpha line It is the lowest energetic transition of the Lyman series due to the small energy gap between the first and second orbicular configurations. Hence, the Lyman-alpha spectral line occurs at the longest wavelength of 121.5 nm. The Rydberg formula is used to calculate the wavelength of the Lyman-alpha spectral line. The Lyman-alpha transition has two specificities. One is that it occurs at the lowest energy than the other electron transition of the Lyman series. And the second is that it occurs at the longest wavelength than the remaining spectral lines of the Lyman series.

8. Frequency calculation for Lyman-alpha line Similarly, the frequency of the Lyman-alpha spectral line is calculated from the following equation. Where, ϒ = frequency of the light radiation c = velocity of light in vacuum λ = wavelength of the light Where, c = 3X108m/sec λ = 121.5 X10-9 m

9. Lyman-alpha: The most intense spectral line The hydrogen spectrum reveals that it is the most intense spectral emission line in its ultraviolet region. This states it is the most abundant hydrogen spectral line in the Lyman series. At suitable temperature conditions, the number of hydrogen atoms participating in the Lyman-alpha transition is more. And it enhances the photon emissions that influence the intensity of the Lyman-alpha spectral line. But, an important thing to remember here is that the intensity of the spectral line does not impact the number of Lyman-alpha spectral lines appearing in the hydrogen spectrum since its transition states remain unchanged. Hence, we observe a thick single Lyman-alpha line at the extreme right end of the hydrogen spectrum.

10. Lyman-alpha: Ozone formation  Lyman-alpha line helps in Ozone formation. Ozone formation  In the upper earth's atmosphere, the oxygen Step-1: Dissociation of Oxygen molecule in to its atoms molecules absorb Lyman-alpha emissions of Step-2: Recombination of oxygen sunrays. And it dissociates the oxygen atom with oxygen molecule to form molecules into their atoms. Ozone  Later, the oxygen atoms combine with the undissociated oxygen molecules to form an Ozone.  In this way, Lyman-alpha emissions help save the earth from harmful radiations by involving in the Ozone formation.

11. Lyman-alpha observations from earth  Strong absorption by the air is the characteristic Lyman-alpha observations property of the Lyman-alpha spectral line.  So, vacuumed spectroscopic equipment is essential in laboratory for Lyman-alpha observations.  For this reason, the Lyman-alpha involved experiments done in satellite-borne instruments, except when observing the extremely distant sources whose redshifts allow the Lyman-alpha line penetrations into the earth's atmosphere.  Therefore, the Lyman-alpha radiations can redshift from faraway celestial objects on to earth's crust.

12. Lyman-alpha fine structures  The Lyman-alpha spectral line splits to give a pair of spectral lines with a slight variation in their wavelengths due to the spin-orbit interaction. Consequently, the Lyman-alpha doublet consists of closely spaced two spectral emission lines at wavelengths of about 121.5668 nm and 121.5674 nm. And they are symbolized as Ly-α3/2 and Ly- α1/2 having j values 3/2 and 1/2, where j is the total angular momentum of the electron.  It realizes Ly-α3/2 is high energy transition than Ly- α1/2. Hence, Ly-α3/2 spectral emission occurs at a slightly shorter wavelength than Ly-α1/2.

13. Importance of Lyman-alpha in cosmology:  The quasars serve as high energetic photon emitters source.  The light radiations emitted from quasars travel through the neutral gaseous clouds. The hydrogen atoms of gas clouds absorb photons having wavelengths matching the Lyman-alpha line.  Hence, the spectra of quasars or distant galaxies show the Lyman-alpha absorption line.

14.  The photon absorbed by the hydrogen atom induces the electron transition between the first and second stationary orbits. And the unstable excited hydrogen electron then returns to its original position with the emission of light radiation at 121.5 nm. It shows the Lyman-alpha spectral emission line in the spectrum.  Both absorption and emission of quasar photons occur concurrently in the universe due to the abundance of neutral hydrogen gas clouds and the quasars.  So, the Lyman-alpha spectral studies help identify the presence of neutral hydrogen atoms in the universe. And it contributes to understanding the properties of celestial matter and its distribution, like hot dark matter.  It helps to calculate the cosmological constant by comparing the angular and radial lengths of the astronomical object at its redshift.

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