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), in contrast to previous studies; this was successfully analysed by Franck-Condon (FC) methods. The sequence of ionic states in the range 7 to 19 eV has been determined by both symmetry adapted cluster configuration interaction and density functional methods, especially using the long-range corrected version of the Becke three-parameter hybrid functional (B3LYP) using the Coulomb-attenuating method (CAM-B3LYP). Both lead to reliable theoretical values for both the calculated vertical and adiabatic ionization energies. The FC profile for the lowest ionization energy (IE1, X(2)A(2)) shows extensive VFS which is analysed successfully. The second IE (A(2)B(1)) shows truncated structure owing to overlap with IE1.

Automated summary

A new synchrotron-based photoionization spectrum of 6,6-dimethylfulvene reveals significant vibrational fine structure (VFS) that was successfully analyzed using Franck-Condon (FC) methods. The order of ionic states in the range of 7 to 19 eV was determined through symmetry adapted cluster configuration interaction and density functional methods, particularly employing the long-range corrected version of the Becke three-parameter hybrid functional (B3LYP) with the Coulomb-attenuating method (CAM-B3LYP). Both methods provide reliable theoretical values for calculated vertical and adiabatic ionization energies. The FC profile for the lowest ionization energy (IE1, X(2)A(2)) exhibits extensive VFS, while the second ionization energy (A(2)B(1)) shows truncated structure due to overlap with IE1.