Theoretical analysis of vibronic structure of absorption spectrum of fulvene

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Abstract
Ab initio and semiempirical quantum‐chemical methods are used to study the lowest two valence excited states of fulvene. A new assignment is proposed for ground state frequencies and the Franck–Condon structure of the S 0→S 1, S 2 transitions is obtained with the help of calculated geometries and vibrational force‐fields of the electronic states involved. It is shown to account very satisfactorily for the observed vibronic structure of the absorption spectra of fulvene. It is demonstrated that, contrary to previous assumptions, CH2 out‐of‐plane vibrational modes play no role in formation of the vibronic structures of the two transitions.