This is part of output file of TD-DFT analysis of a molecule. My question is that if I want to do assignment corresponding to excited state 1, how would i come to know, whether it is pai to pai* or n to pai* transition.
Excited State 1: Singlet-A 3.7746 eV 328.47 nm f=0.0681
71 -> 76 0.14554
72 -> 73 0.66092
This state for optimization and/or second-order correction.
Total Energy, E(RPA) = -1245.04053734
Copying the excited state density for this state as the 1-particle RhoCI density.
Excited State 2: Singlet-A 4.6647 eV 265.79 nm f=0.0590
68 -> 73 0.41032
69 -> 73 0.41521
70 -> 73 0.25779
71 -> 73 -0.24279
Excited State 3: Singlet-A 4.7881 eV 258.94 nm f=0.3652
68 -> 73 0.20008
69 -> 73 0.14131
71 -> 73 0.53757
72 -> 74 -0.29181
Excited State 4: Singlet-A 4.8407 eV 256.13 nm f=0.0656
68 -> 73 0.10648
71 -> 73 0.24108
72 -> 74 0.63660
Excited State 5: Singlet-A 4.8994 eV 253.06 nm f=0.0012
72 -> 75 0.70050
Most straightforward way is to visualize your orbitals (but please, keep in mind, that different visualizing and computational software can start numeration of orbitals either from 0 or from 1). Then you will hopefully be able to determine, which types they correspond to.
The character of the transition is determined by the composition of the donor and acceptor orbitals. For instance, in the first excited state, the moexcitation with the high contribution to the excited state wavefunction is 72->73, which is HOMO->LUMO. Then, to known if this transition is pi->pi*, n->pi*, etc, it is necessary to analize the atomic orbitals contributions to the HOMO and LUMO, i.e if the molecular orbital is showing sigma or pi bonds, or non-bonding d orbitals, etc.
If we use as example the first transition you have: the most of the transition is due to the orbital 72 -> 73, observing the shapes of the MOs you can define if they are pi, n, or pi*. You can determine qualitatively whether they are pi, n or pi* also comparing the absolute energies of the orbitals toward the Fermi level.
use swizard softwarer for assignments. I have use this for the assignments
Morteza jamshidi, how to calculate orbital contribution in electronic transitions by using chemssian?
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