The table displays the symmetry species (C 2v ) to which the atomic orbitals (or combination thereof: case of the hydrogen orbitals, which individually do not belong to 54 combination thereof: case of the hydrogen orbitals, which individually do not belong to any symmetry species of the group) belong. Only atomic orbitals of the same symmetry can combine, and the combination belongs to the same symmetry. For instance, the combination 1s(H 1 )+1s(H 2 ) is of symmetry A 1 and can combine only with atomic orbitals of this symmetry (1s(O), 2s(O), 2p z (O). The combinations are molecular orbitals of A 1 symmetry: 1a 1 , 2a 1 , 3a 1 and 4a 1 , which differ in the proportion of the mix (1a 1 is basically the 1s(O) orbital), 2a 1 is the mix of the 2s(O) and the 1s(H 1 )+1s(H 2 ) , and so on. Remember that, besides having the same symmetry, effective mixing requires similarity of energies of the orbitals taking part. Once the MO diagram is known, you must fill in the corresponding electrons (careful, if you only took into account a specific subset of orbitals –eg the p orbitals in a conjugated planar molecule –only the corresponding electrons need to ba accounted for –in the example suggested of the p orbitals, just the π electrons). Then, as happens with atoms, the ELECTRONIC CONFIGURATION of the molecule is a list of the orbitals in increasing order of energies and as a superscript the occupation number. In the case of molecular orbitals, the name is just the symmetry species of the orbital in lowercase, and preceeded by the ordinal number of that orbital (that is, “1” for the first orbital of that symmetry, “2” for the second, and so on. The electronic configuration of water is written as an example under the MO diagram above. Unit 3: Electronic Spectroscopy

Spectroscopy 03 Electronic Spectroscopy Slide54

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The table displays the symmetry species (C2v) to which the atomic orbitals (or combination thereof: case of the hydrogen orbitals, which individually do not belong to

54

combination thereof: case of the hydrogen orbitals, which individually do not belong to any symmetry species of the group) belong.

Only atomic orbitals of the same symmetry can combine, and the combination belongs to the same symmetry. For instance, the combination 1s(H1)+1s(H2) is of symmetry A1 and can combine only with atomic orbitals of this symmetry (1s(O), 2s(O), 2pz(O). The combinations are molecular orbitals of A1 symmetry: 1a1, 2a1, 3a1 and 4a1, which differ in the proportion of the mix (1a1 is basically the 1s(O) orbital), 2a1 is the mix of the 2s(O) and the 1s(H1)+1s(H2) , and so on. Remember that, besides having the same symmetry, effective mixing requires similarity of energies of the orbitals taking part.

Once the MO diagram is known, you must fill in the corresponding electrons (careful, ifyou only took into account a specific subset of orbitals eg the p orbitals in a conjugatedplanar molecule only the corresponding electrons need to ba accounted for in theexample suggested of the p orbitals, just the electrons).

Then, as happens with atoms, the ELECTRONIC CONFIGURATION of the molecule isa list of the orbitals in increasing order of energies and as a superscript the occupationnumber. In the case of molecular orbitals, the name is just the symmetry species of theorbital in lowercase, and preceeded by the ordinal number of that orbital (that is, 1 forthe first orbital of that symmetry, 2 for the second, and so on. The electronicconfiguration of water is written as an example under the MO diagram above.

Unit 3: Electronic Spectroscopy