Question

Urgent! For selectrion rules in UV-vis spec, what is B3U*B2U*B2g and B2U*B1U*B2g?

Answer 1

actually UV-vis spectroscopy, the electronic transition will occur from ground state to excited state. every electronic state has some symmetry. so by orbital selection rule, the direct product of (symmetry of final state)*(symmetry of light direction)*(symmetry of initial; state) should be totally symmetric: i.e. should belong to A1g symmetry.

here, B3U*B2U*B2G.

B3u is final state symmetry, B2U is light radiation polarization direction, B2G is initial state symmetry. To make symmetrically allowed, the direct product should be totally symmetric.

similarly, in B2U*B1U*B2G

B2U is final state symmetry, B1U is light radiation polarisation symmetry, B2g is initial state symmetry.