The term "metastable levels" refers to
A) regions within a molecular cloud that are not moving relative to the rest of the cloud.
B) the upper energy level of the 21-cm transition in the hydrogen atom.
C) the lower energy level of the 21-cm transition in the hydrogen atom.
D) the boundary layers between HI regions and the hotter intercloud medium.
E) energy levels in an atom that require a much longer time than average to decay and emit a photon.

Question

Quizplus · Accepted Answer

Metastable levels are energy levels in an atom that have a longer lifetime before decaying and emitting a photon, due to forbidden transitions or other factors.

The Term "Metastable Levels" Refers to