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{{Short description|Quantum Collection topic on Quantum Spectral lines and series}}
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'''Spectral lines''' are discrete wavelengths of light emitted or absorbed by atoms and molecules, arising from transitions between quantized energy levels, and they provided some of the earliest direct evidence for quantum theory.<ref>[https://www.britannica.com/science/spectral-line Spectral line – Britannica]</ref>
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[[File:Quantum_spectral_lines_and_series.svg|thumb|400px|Spectral lines arise from discrete electronic transitions in atoms, forming characteristic series such as Lyman, Balmer, and Paschen.]]
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'''Spectral lines and series''' spectral lines are discrete wavelengths of light emitted or absorbed by atoms and molecules, arising from transitions between quantized energy levels, and they provided some of the earliest direct evidence for quantum theory. In quantum mechanics, electrons in atoms occupy discrete energy eigenstates. The hydrogen atom provides the simplest and most important example of spectral line structure. Its energy levels are given by: Transitions between these levels produce series of spectral lines described by the Rydberg formula: This relation accurately predicts observed hydrogen spectral lines. When an electron transitions between two states, a photon is emitted or absorbed with energy given by: This leads to sharply defined spectral lines rather than a continuous spectrum.
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[[File:Quantum_spectral_lines_and_series.svg|thumb|280px|Quantum Spectral lines and series.]]
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== Origin of spectral lines ==
== Origin of spectral lines ==
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==References==
==References==
{{reflist|3}}
{{reflist|3}}
== Historical names ==
* [[Biography:William Hyde Wollaston|William Hyde Wollaston]] observed dark lines in the solar spectrum in 1802, before Fraunhofer mapped them systematically. These observations became part of the experimental history of spectroscopy and quantum atomic transitions.
* [[Biography:Joseph von Fraunhofer|Joseph von Fraunhofer]] mapped dark absorption lines in the solar spectrum. Fraunhofer lines became a key observational background for spectroscopy and the later quantum explanation of atomic transitions.
{{Author|Harold Foppele}}
{{Author|Harold Foppele}}


{{Sourceattribution|Quantum Spectral lines and series|1}}
{{Sourceattribution|Physics:Quantum Spectral lines and series|1}}

Latest revision as of 09:02, 23 May 2026

← Back to Atomic and spectroscopy Book I
← Previous : Stark effect
Next : Selection rules →

Spectral lines and series spectral lines are discrete wavelengths of light emitted or absorbed by atoms and molecules, arising from transitions between quantized energy levels, and they provided some of the earliest direct evidence for quantum theory. In quantum mechanics, electrons in atoms occupy discrete energy eigenstates. The hydrogen atom provides the simplest and most important example of spectral line structure. Its energy levels are given by: Transitions between these levels produce series of spectral lines described by the Rydberg formula: This relation accurately predicts observed hydrogen spectral lines. When an electron transitions between two states, a photon is emitted or absorbed with energy given by: This leads to sharply defined spectral lines rather than a continuous spectrum.

Quantum Spectral lines and series.

Origin of spectral lines

In quantum mechanics, electrons in atoms occupy discrete energy eigenstates. When an electron transitions between two states, a photon is emitted or absorbed with energy given by:

E=hν=Ei−Ef

where:

  • h is Planck’s constant
  • ν is the frequency of the radiation
  • Ei, Ef are the initial and final energy levels

This leads to sharply defined spectral lines rather than a continuous spectrum.[1]

Hydrogen spectral series

The hydrogen atom provides the simplest and most important example of spectral line structure. Its energy levels are given by:

En=−13.6 eVn2

Transitions between these levels produce series of spectral lines described by the Rydberg formula:

1λ=R(1nf2−1ni2)

where:

  • R is the Rydberg constant
  • ni>nf

This relation accurately predicts observed hydrogen spectral lines.[2]

Major series

  • Lyman series (nf=1) – ultraviolet region
  • Balmer series (nf=2) – visible region
  • Paschen series (nf=3) – infrared region
  • Brackett series (nf=4) – infrared
  • Pfund series (nf=5) – far infrared

Each series corresponds to transitions ending at a fixed lower energy level.[3]

Fine structure and splitting

Real spectral lines are not perfectly sharp. They exhibit splitting due to additional physical effects:

  • Fine structure — relativistic corrections and spin–orbit coupling
  • Zeeman effect — splitting in an external magnetic field
  • Stark effect — splitting in an electric field

These effects reveal deeper structure in atomic energy levels.[4][5]

Selection rules

Not all transitions are allowed. Selection rules determine which spectral lines appear:

  • Δl=±1
  • Δm=0,±1

These arise from conservation of angular momentum and symmetry properties of atomic wavefunctions.[6]

Spectroscopy and applications

Spectral lines are fundamental in many areas of physics and astronomy:

  • Identifying chemical elements in stars and galaxies
  • Measuring Doppler shifts and cosmic expansion
  • Determining temperatures and densities of plasmas
  • Laser technology and atomic clocks

Each element has a unique spectral “fingerprint.”[7]

See also

Table of contents (217 articles)

Index

Full contents

References

  1. ↑ Spectroscopy in Astronomy – OpenStax
  2. ↑ Strong Lines of Hydrogen – NIST
  3. ↑ Bohr’s Theory of the Hydrogen Atom – OpenStax
  4. ↑ Zeeman effect – Britannica
  5. ↑ Stark effect – Britannica
  6. ↑ Atomic Spectra and X-rays – OpenStax
  7. ↑ Spectroscopy: Applications – Britannica

Historical names

  • William Hyde Wollaston observed dark lines in the solar spectrum in 1802, before Fraunhofer mapped them systematically. These observations became part of the experimental history of spectroscopy and quantum atomic transitions.
  • Joseph von Fraunhofer mapped dark absorption lines in the solar spectrum. Fraunhofer lines became a key observational background for spectroscopy and the later quantum explanation of atomic transitions.


Author: Harold Foppele


Source attribution: Physics:Quantum Spectral lines and series

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