SINGLET-SINGLET ELECTRON TRANSITIONS IN ISOELECTRONIC MONOSUBSTITUTED BENZENES - SEMIEMPIRICAL STUDY BY A MODIFIED CNDO-CI METHOD

A modified CNDO-CI method is presented which assigns the singly excited singlet configurations to the different irreducible representations and separately diagonalizes the resulting blocks in the Hamiltonian CI matrix, using the same number of effectively interacting terms for each irreducible representation (annihilation of interaction terms by the ZDO approximation being duly taken into account). Parameterization has been adjusted to fit a set of 25 experimentally well established O-O transition energies of different monocyclic compounds and the method has been applied to the first four transitions of the isoelectronic set of toluene, aniline, phenol and fluorobenzene. Attention has been paid to changes in dipole moments and in electron charge distributions, using population analysis and electron density maps, after suitable deorthogonalization of the bond order matrix. © 1978.