Resonance Raman spectra of copper tetraphenylporphyrin: Effects of strong vibronic coupling on excitation profiles and the absorption spectrum

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Abstract
Raman excitation profiles of copper tetraphenylporphyrin have been obtained and interpreted in terms of strong vibronic coupling. The Duschinsky mixing of normal modes in the excited Q electronic state has a dominant effect on the excitation profiles and the absorption spectrum. A general theoretical technique for calculating the vibronic states of molecules is described and applied to metalloporphyrins. The analytical expressions obtained from a new perturbation treatment of the vibronic problem permit a detailed physical understanding of strong coupling influences and interference effects observed in copper tetraphenylporphyrin excitation spectra. A modified interpretation of the Q band absorption is indicated.