A Study of the Ionization Spectrum of 6,6-Dimethylfulvene Using Algebraic-Diagrammatic Construction and Coupled Cluster Methods

The electronic structure and ionization spectrum of 6,6-dimethylfulvene were calculated using the third-order algebraic-diagrammatic construction method for the one-particle Green’s function (IP-ADC(3)) and the equation-of-motion coupled-cluster method at the level of singles and doubles model (IP-EOM-CCSD). The results were used to interpret the recently obtained photoelectron spectrum of 6,6-dimethylfulvene (M.H. Palmer et al., Chem. Phys. Lett. 796 , 139558 (2022)). A number of new assignments have been proposed, among which the most significant is the assignment of the previously unassigned shoulder of the third photoelectron band at 10.5 eV, which, according to our IP-ADC(3)-calculations, is formed by the satellite transitions associated with the 2a 2 and 2b 1 π-orbitals of the fulvene ring. The data obtained in this study also suggest that using the IP-EOM-CCSD method and equivalent approaches involves difficulties with correct description of the satellite states.