[MrHappy0]

Here is the text I am trying to comprehend: The intensity (extinction coefficient) is determined by selection rules. -In an octahedral (Oh) complex, ̂μel transforms as T1u. - We can use group theory to do the math: f=< Ψg| ̂μel|Ψg>

-For f ≠ 0, f must be A1g because all other irreducible representations are anti-symmetric with respect to at least one coordinate → integral over all space goes to zero! -Laporte selection rule: consider character of i. ̂μel is a vector, so it always has “u” parity. - f = <A|u|B> -Transitions between states of opposite parity (A=g, B=u or A=u, B=g) are “Laporte allowed”. -Transitions between states of the same parity (A=B=g or A=B=u) are “Laporte forbidden”. - d orbitals are a binary product of Cartesian coordinates (z2, xy, etc.) →always have “g” parity. -d → d electronic transition are Laporte forbidden (low intensity). -Spin selection rule: transitions between states with different

A few questions to get this discussion started: When the word "states" is used, is this implying to electronic states such as the ground state or excited state? What is "g" and "u"? Gerade and ungerade?

[Corribus]

A few questions to get this discussion started: When the word "states" is used, is this implying to electronic states such as the ground state or excited state? What is "g" and "u"? Gerade and ungerade?

For electronic transitions, "state" refers to electronic ground state and electronic excited states.  g and u refers to gerade and ungerade, which IIRC comes from German for even and odd. If you're using group theory, the g/u refers to whether the character of the inversion operator (i) is +1 or -1 (or larger magnitudes for multidimensional representations).