Atomic emission spectroscopy

Atomic emission spectroscopy (AES) is a method of chemical analysis that uses the intensity of light emitted from a flame, plasma, arc, or spark at a particular wavelength to determine the quantity of an element in a sample. The wavelength of the atomic spectral line in the emission spectrum gives the identity of the element while the intensity of the emitted light is proportional to the number of atoms of the element. The sample may be excited by various methods.

Atomic Emission Spectroscopy allows us to measure interactions between electromagnetic radiation and physical atoms and molecules. This interaction is measured in the form of electromagnetic waves representing the changes in energy between atomic energy levels. When elements are burned by a flame, they emit electromagnetic radiation that can be recorded in the form of spectral lines. Each element has its own unique spectral line due to the fact that each element has a different atomic arrangement, so this method is an important tool for identifying the makeup of materials. Robert Bunsen and Gustav Kirchhoff were the first to establish atomic emission spectroscopy as a tool in chemistry.^[1]

When an element is burned in a flame, its atoms move from the ground electronic state to the excited electronic state. As atoms in the excited state move back down into the ground state, they emit light. The Boltzmann expression is used to relate temperature to the number of atoms in the excited state where larger temperatures indicate a larger population of excited atoms. This relationship is written as:

${\frac {n_{upper}}{n_{lower}}}={\frac {g_{upper}}{g_{lower}}}e^{-(\varepsilon _{upper}-\varepsilon _{lower})}/k_{B}T$

where n_upper and n_lower are the number of atoms in the higher and lower energy levels, g_upper and g_lower are the degeneracies in the higher and lower energy levels, and ε_upper and ε_lower are the energies of the higher and lower energy levels. The wavelengths of this light can be dispersed and measured by a monochromator, and the intensity of the light can be leveraged to determine the number of excited state electrons present.^[2] For atomic emission spectroscopy, the radiation emitted by atoms in the excited state are measured specifically after they have already been excited.

Much information can be obtained from the use of atomic emission spectroscopy by interpreting the spectral lines produced from exciting an atom. The width of spectral lines can provide information about an atom’s kinetic temperature and electron density. Looking at the different intensities of spectral lines is useful for determining the chemical makeup of mixtures and materials. Atomic emission spectroscopy is mainly used for determining the makeup of mixes of molecules due to the fact that each element has its own unique spectrum.^[3]

^ Thakur, Surya N. (2020-01-01), Singh, Jagdish P.; Thakur, Surya N. (eds.), "Chapter 2 - Atomic emission spectroscopy", Laser-Induced Breakdown Spectroscopy (Second Edition), Amsterdam: Elsevier, pp. 23–40, doi:10.1016/b978-0-12-818829-3.00002-2, ISBN 978-0-12-818829-3, retrieved 2024-11-13
^ Engel, Thomas; Hehre, Warren J.; Angerhofer, Alex (2019). Quantum chemistry and spectroscopy: physical chemistry (Fourth ed.). New York: Pearson. ISBN 978-0-13-480459-0.
^ Lajunen, Lauri H.; Perämäki, P.; Lajunen, Lauri H. J. (2004). Spectrochemical analysis by atomic absorption and emission. Royal Society of Chemistry (2. ed.). Cambridge: Royal Society of Chemistry. ISBN 978-0-85404-624-9.

[1] Thakur, Surya N. (2020-01-01), Singh, Jagdish P.; Thakur, Surya N. (eds.), "Chapter 2 - Atomic emission spectroscopy", Laser-Induced Breakdown Spectroscopy (Second Edition), Amsterdam: Elsevier, pp. 23–40, doi:10.1016/b978-0-12-818829-3.00002-2, ISBN 978-0-12-818829-3, retrieved 2024-11-13

[2] Engel, Thomas; Hehre, Warren J.; Angerhofer, Alex (2019). Quantum chemistry and spectroscopy: physical chemistry (Fourth ed.). New York: Pearson. ISBN 978-0-13-480459-0.

[3] Lajunen, Lauri H.; Perämäki, P.; Lajunen, Lauri H. J. (2004). Spectrochemical analysis by atomic absorption and emission. Royal Society of Chemistry (2. ed.). Cambridge: Royal Society of Chemistry. ISBN 978-0-85404-624-9.

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