Electronic structure and photochemical rearrangements of matrix-isolated C 8H 10 radical cations

Abstract

The C 8H 10 isomers 1,3,5,7-octatetraene (OTE), 1,3,5-cyclooctatriene (COT) and bicyclo[4.2.0]octa-1,4-diene (BCO) were subjected to ionization by X-irradiation in argon matrices at 20 K. The electronic structure of the parent radical cations is discussed on the basis of their spectral properties and qualitative theoretical considerations. Photolysis of the cyclic cations leads to the formation of OTE 1 1 In polyene cations, a clear distinction between single and double bonds can no longer be made. We have therefore proposed 3 to use the general term “rotamers” instead of conformers (pertaining to rotation around single bonds) or isomers (for double bond rotamers) to distinguish between different planar or periplanar linear polyene cations of a given composition. We will use the E/Z nomenclature to describe the geometry of individual polyene cation rotamers. in at least six different conformation which can be distinguished by selective bleaching experiments. The complex band structure of the all- trans-OTE 1 absorptions is demonstrated to arise from the presence of this species in at least five different matrix sites. By very narrow-bandwidth irradiation, single sites can be bleached or populated and the resulting difference spectra allow a detailed vibronic analysis of all- trans-OTE 1