RESONANCE RAMAN AND QUANTUM-CHEMICAL STUDIES OF SHORT POLYENE RADICALCATIONS

The results of our investigations of the geometric and vibrational str uctures of some short conjugated polyene radical cations are reported. The radical cations of 1,3-butadiene and three of its deuterated isot opomers, trans- and cis-1,3-pentadiene, 2-methyl-1,3-butadiene, and E- and Z-1,3,5-hexatriene have been studied. The radical cations were ge nerated radiolytically in a glassy Freon matrix and investigated by op tical absorption and resonance Raman spectroscopy. Ab initio and densi ty functional molecular-orbital calculations have been carried out to predict equilibrium structures and to assist assignment of the resonan ce Raman spectra. A new and improved scaled quantum mechanical force f ield for the butadiene radical cation was also determined. The presenc e of more than one rotamer was observed in all the polyene radical cat ions we investigated. (C) 1997 Elsevier Science B.V.