Anomalous intensity ratios in the excitation protides of vibronicaiIy active fundamentals in the Q-band of porphyrins are shown to be due to interference between intramanifold (J&n-Teller) coupling with the Q and B bands, intermanifold (Herzberg-Teller) coupling between the Q and B bands. and electronic confgumtion interaction beheen the onecIectron representations of the corresponding excited states_ Despite their compfexity, metfloporphytins have provided someof the best exampIes of the successful disentanglement of vibronicall~contaminated spectra by resonance Raman spectroscopy [l-6]. These molecules whose basic point group symmetry is Dan, have two Iowenergy, doubly generate (E-type) electronically excited states subject to intramanifoId or J&n-Teller (JT) coupling and intermanifold or Herzberg-Teller (HT) coupling. Of these two states, the one of the lower energy (Q-band) shows a weak and the other, separated from the first by a gap of 6000-7000 cm-t (Sor e t or B-band), shows a strong absorption_ Of the modes that can couple these states through the HT mechanizrs, namely those belonging to the representations ale, big, b2e and aXg, the first three are aIso active in intramanifold couphng [S-7] _ In this note we shah show that a superposition of these coupling mechanisms can account for the observed Raman excitation profiles, provided one departs in some cases from the conventional Gouterman model [8] _ Irr the four-orbitat model of Gouterman [S] , the B" and Q0 states are symmetric and antisymmetric combinations of the singly excited configurations arising from an eiectron promoted to the doubly degenerate orbitals from the two highest occupied orbitak In this approximation, the transition moments of these configurations (nearly) cancel in the Qo band-The Q band acquires (most of) its O-O intensity through a residual configuration interaction (Cl) between these zero&order Bo and Qo states, the interaction energy being one haIf of the energy difference between the highest occupied 3azu and La Iu molecular orbitaIs (8]_ It has been shown [9] that the JT coupling also vanishes in the four-orbital model (Bu and Qo basis set) if only one-electron terms are retained, so that ksued zzs NRCC No-17844. * Research Associate.