allowed transition

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A transition between two electronic states allowed according to selection rules associated with group theory. The probability of a transition between states m and n produced by the interaction of electromagnetic radiation with an atomic system is proportional to the square of the magnitude of the matrix elements of the electric dipole moment. If this quantity is not zero, the transition is an allowed transition; if it is zero the transition is a forbidden transition as a dipole transition. It may, however, be an allowed transition for magnetic dipole or quadrupole-moment transitions, which have much smaller transition probabilities and consequently give much weaker lines in the spectrum.

Subjects: Chemistry.

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