I have a question about allowed transitions and molecular states. For an electric dipole transition between two states (say molecular or atomic) to have a non-zero probability of occurring, the transition dipole moment [itex]\langle \psi_{f}|\textbf{μ}\left|\psi_{i} \right \rangle[/itex] must be non-zero. This can be determined by considering the irreducible symmetry representations to which each state/operator belongs i.e. [itex]\Gamma ( \psi_{f} ) \otimes \Gamma \left(x,y,z \right) \otimes \Gamma \left(\psi_{i}\right) [/itex] must contain the totally symmetric irreducible representation at least once.(adsbygoogle = window.adsbygoogle || []).push({});

My question is, are the initial states and final states to be considered the overall molecular states or the individual single electron states? e.g. in diatomic hydrogen, for a [itex]\sigma_{g} \rightarrow \sigma_{u}[/itex] transition, are the initial and final states the electron states of the electron being excited or the overall initial and final molecular states (i.e. of both electrons)?

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# Molecular States, Symmetry and Allowed Transitions

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