The single configuration SCF calculation for excited states is proposed for the various differently optimized excited states. Different sets of occupied and unoccupied one-electron orbitals are obtained for the different excited states. Morokuma's model is extended to a semiempirical CNDO basis. The method predicts excited state geometry quite well. Qualitative agreement in the calculated transition energies, singlet-triplet splitting and barrier to inversion has been found and the results indicate no major deviation in the trends followed in similar non-iterative simple hole-potential calculation. As expected, convergence could not be achieved in all1ππ* calculations in the non-planar geometry. Calculations in the planar geometry, however, showed convergence with difficulty. One interesting feature is a gradual decrease in the energy difference between3ηπ* and3ππ* states with successive fluorine substitution, ultimately leading to an inversion in the order in F2CS. The prediction of3ππ* as theT1 state in F2CS is discussed in the context of photochemistry exhibited by certain aromatic carbonyl compounds. Probable extension of the present model to develop an average Fock operator for single excitations and also a one-electron operator for double excitations is proposed.
Volume 134, 2022
Continuous Article Publishing mode
Click here for Editorial Note on CAP Mode