Explain in your own words why the electronic transitions.
The allowed electronic transitions occur with the change in the electronic charge distribution in an atom or a molecule. This electronic charge distribution is referred to as a dipolar shift. The initial wavefunction can describe the state of an electron; the electron has the probabilities of.It follows that the electric dipole matrix elements,, which control the rates of so-called electric dipole transitions, via Equations (8.172)-(8.174), are only non-zero if (8.172) (8.173) (8.174).The above selection rules apply only for the Electric Dipole (E1) approximation. Higher order terms in the expansion, like the Electric Quadrupole (E2) or the Magnetic Dipole (M1), allow other decays but the rates are down by a factor of or more. There is one absolute selection rule coming.
Forbidden Transitions Atomic transitions which are forbidden by the electric dipole selection rules and are unsurprisingly known as forbidden transitions. It is clear from the analysis in Sect. 13.8 that a forbidden transition is one for which the matrix element is zero.Additionally, because all three components of the magnetic dipole operator transform as the same irrep, this electronic transition will be allowed if you apply a magnetic field along any of the three Cartesian axes in the molecular frame.
The x, y, and z components of the transition dipole moment operator have u inversion symmetry in molecule with inversion center (g and u are short for gerade and ungerade in German, meaning even and odd). The electronic transition moment integral need to yield totally symmetric irreducible representation A g for allowed transitions. Therefore.
