Astrophysics (index)

Metastable

(characteristic of an excited state that lasts longer than typical)

A Metastable State of Excitation is one that lasts longer than typical, e.g., lasts seconds, minutes, or hours rather than a tiny fraction of a second. Examples:

  • The Hydrogen (H) state that can relax producing the 21cm Line.
  • A Helium (He) state (combination of spins when one of the electrons) is excited, that can last a couple of hours before relaxing.

Metastable states are often a part of Forbidden Lines: they are often so delicate that any disturbance will cause them to relax, and are unlikely to live out their undisturbed life unless unlikely to come near to another molecule, e.g., in a near vacuum.


(atoms)
http://en.wikipedia.org/wiki/Metastability

Referenced by:
Helium (He)

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