An Etymological Dictionary of Astronomy and Astrophysics
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A → recombination line whose wavelength lies in the radio range of the electromagnetic spectrum. Radio recombination lines are the result of electronic transitions between high energy levels (n > 50) in an atom or ion.

→ radio; → recombination line.

An → emission line in a spectrum produced in an → H II region when a free electron combines with an ionized atom to form a neutral atom or an ion of lower → ionization stage. Same as → free-bound emission.

→ recombination; → line.