The ionized states of 6,6-dimethylfulvene; the vibrational energy levels studied by photoionization, configuration interaction and density functional calculations

A new synchrotron-based photoionization spectrum of 6,6-dimethylfulvene shows significant vibrational fine structure (VFS) which was successfully analysed by Franck-Condon (FC) methods. The sequence of ionic states in the range 7 to 19 eV has been determined by symmetry adapted cluster configuration interaction and Roothaan-Hartree-Fock open shell methods, leading to reliable theoretical values for both the calculated vertical and adiabatic ionization energies. The FC profile for the lowest ionization energy (IE1, X2A2) shows extensive VFS which is analysed successfully. The second IE (A2B1) shows truncated structure owing to overlap with IE1