An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 2 Search : forbidden line
forbidden line
  خط ِ بژکم   
xatt-e bažkam

Fr.: raie interdite   

A spectral line emitted by atoms undergoing energy transitions not normally allowed by the → selection rules of → quantum mechanics. Forbidden emission lines form in low-density interstellar gas and are collisionally excited. They are designated by enclosing in brackets, e.g. [O III] and [N II], O and N representing oxygen and nitrogen atoms respectively.

forbidden; → line.

semi-forbidden line
  خط ِ نیمه-بژکم   
xatt-e nime-bažkam

Fr.: raie semi-interdite   

A → spectral line for which the upper and lower → energy levels have different values of S, the total → spin angular momentum. These lines violate the quantum mechanical → selection rule under → LS coupling, ΔS = 0. For example, the Ca I λ6573 line results from transition between the upper → triplet state (3P1) with a total spin angular momentum S = 1 and the → ground state, a → singlet state (1S0, total spin angular momentum S = 0). A semi-forbidden line is marked by a right bracket following the atom name, i.e. Ca I], in the above-mentioned case. Same as → interconnection line and → intersystem line.

semi-; → forbidden; → line.