Explain ‘Selection rules’ that basically decide which transitions are ‘allowed or forbidden’ in spectroscopy
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The possible radiative transitions are classified as either allowed or forbidden, depending on the probability of their occurrence. In some instances, as, for example, when both the initial and final states have a total angular momentum equal to zero, there can be no single photon transition between states of any kind. The allowed transitions obey certain restrictions, known as selection rules
Forbidden transitions proceed slowly compared to the allowed transitions, and the resulting spectral emission lines are relatively weak. For atoms in about the first third of the periodic table, the L and S selection rules provide useful criteria for the classification of unknown spectral line
Forbidden transitions proceed slowly compared to the allowed transitions, and the resulting spectral emission lines are relatively weak. For atoms in about the first third of the periodic table, the L and S selection rules provide useful criteria for the classification of unknown spectral line