SEMIEMPIRICAL STUDY ON THE ELECTRONIC-SPECTRA OF MODEL CYANOMETMB

Semiempirical INDO calculations were carried out on the ground state and excited states of model CyanoMetMb. It is shown that the ground state has a \...d(xy)2d-pi-3> configuration, the correct description of which requires a wave function that has symmetric electron distributions in the two Fe(III) d-pi orbitals. Four ''extra'' xy-polarized absorptions with absorption frequencies lower than the Q bands were found with the S-CI calculations, in agreement with the single-crystal polarized absorption spectra. These absorptions are predominantly excitations from the highest two occupied porphyrin orbitals (3a2u and 1a1u) to the two lowest unoccupied orbitals (4e(g)) with spin couplings between porphyrin and Fe(III). Mixing of porphyrin to Fe(III) charge-transfer excitations, (3a2u, d-pi) and (1a1u, d-pi), into these wave functions results in nonzero oscillator strengths for these transitions.