doublet

spectroscopy

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June 25, 2026

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In spectroscopy, fine structure refers to the splitting of an atom's main spectral lines into multiple components, each with a slightly different wavelength. This splitting occurs when an atom transitions between energy states, and it arises from the interaction between an electron's orbital motion and its quantum mechanical "spin".1

An electron, acting like a tiny magnet due to its spin, interacts with the magnetic field generated by its movement around the nucleus. This interaction causes the fine structure. In atoms like alkali metals, this splitting results in two components, known as doublets. The separation of these doublets generally increases with the atomic number of the element.1

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fine structure
…components of fine structure (called doublets), while in atoms of alkaline earths there are three components (triplets). This arises because the atoms of alkali metals have only one electron outside a closed core, or shell, of electrons, while the atoms of alkaline earths have two such electrons. Doublet separation for…
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…components of fine structure (called doublets), while in atoms of alkaline earths there are three components (triplets). This arises because the atoms of alkali metals have only one electron outside a closed core, or shell, of electrons, while the atoms of alkaline earths have two such electrons. Doublet separation for…
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