A Short Note On Types Of The Hydrogen Spectrum

During the discharge of electricity in a low-pressure tube consisting of hydrogen gas, the emission of radiation takes place. This radiation is further analyzed using a spectrograph, giving us a series of lines. This combined line spectrum is called the hydrogen atomic spectrum. Each line of this hydrogen atomic spectrum indicates a different wavelength of light. In this way, the hydrogen atomic spectrum is characterized by six different series of lines. These series in the spectrum of hydrogen are the Lyman, Balmar, Paschen, Brackett, Pfund and Humphrey series which are named after the person who found them. 

Physics behind the spectrum

As per Bohr’s theory, if an electron stays in its orbit, that electron will not emit or absorb any energy. When a hydrogen atom is placed in an electric discharge under low pressure and high temperature, its electron gets shifted to the outer orbit. This excitation cannot last long, and thus the electron returns to its natural orbit by emitting a photon. The emitted photon carries the same energy as the difference between the energy level of the used two-orbit of the electron. 

For each value of n1 in the Rydberg equation, say n1= 1,2,3,4… so on, the observed wavelength corresponds to different hydrogen spectrum series. 

• In the Lyman series, the value of n1 is equal to one (n1=1) 

• In the Balmer series, the value of n1 is equal to two (n1=2)

Significance of these infinite levels

If an electron gets excited to n2 = infinite, the energy absorbed by the electron is equal to the energy of that orbit and the atom is in an ionized (positively) state. 

Characteristics of hydrogen spectrum series and its types

When an electron is excited to an outer orbit, it uses different routes to get to its original or lower orbits. These transitions from higher orbit to lower orbit lead to the emission of many lines in the hydrogen spectrum. 

These lines are mainly six groups in the hydrogen atomic spectrum. These are:

• Lyman series 

• Balmer series

• Paschen series

• Brackett series

• Pfund series

• Humphrey series

• Lyman series: When an electron transition takes place from a higher-level orbit, i.e. n2=2,3,4,5,…. to the first orbit (n1=1), the produced lines on the spectrum correspond to the Lyman series. The wavelength of the produced photons lies in the ultraviolet region. Theodore Lyman discovered this series.
• Balmer series: This series was discovered by Johann Balmer. When an electron transition takes place from a higher-level orbit, i.e. n2=3,4,5,6 …, to the second orbit (n2=2), the produced lines on the spectrum correspond to the Balmer series. These Balmer series lines lie in the visible region and have a wavelength range of 700 nm-400 nm. 
• The Paschen series consists of lines corresponding to the transition of an electron from n2=4,5,6,7… and so on to n1=3. This series was named after Friedrich Paschen and the wavelength lies in the infrared band. The wavelength range of this series is 820 nm-1875 nm.
• Brackett series: When an electron transition takes place from a higher-level orbit, i.e. n2=5,6,7,8…. to the first orbit (n1=4), the produced lines on the spectrum correspond to the Brackett series. The wavelength of the producer, Frederick Summer Brackett.
• Pfund series: This series was discovered by August Herman Pfund. When an electron transition takes place from a higher-level orbit, i.e. n2=6,7,8,9 … to the second orbit (n2=5), the produced lines on the spectrum correspond to the Pfund series. These produced lines lie in the visible region with a wavelength range of 2279 nm-7460 nm.
• Humphrey series: This series was discovered by Curtis J. Humpherys. When an electron transition takes place from a higher-level orbit, i.e. n2=7,8,9 … to the second orbit (n2=6), the produced lines on the spectrum correspond to the Humphery series. These produced lines lie in the visible region with a wavelength range of -3282 nm-12370 nm.

Conclusion

The emission of a photon by the transition of an electron from one orbit to another can produce a hydrogen atomic spectrum. This spectrum consists of various light rays corresponding to numerous wavelengths. These observed wavelengths are grouped based on landing orbit and are classified into six groups named Lyman, Balmar, Paschen, Brackett, Pfund and Humphrey.