Can substituted benzenes be used as building blocks in core electron shake-up spectra? Original Research Article

We present calculations on X-ray photoelectron shake-up spectra of mono-substituted benzenes in order to explore possible systematic trends of these spectra on strength of substitution. Most spectral intensity derives from shake transitions from the few highest occupied π molecular orbitals to the lowest, unoccupied π∗ orbital. Spectra referring to the ring carbons show alternancy of energy and intensity with respect to site. They are shifted within an experimentally unresolved sub-eV energy range if the core site is unconnected to the substituent, while by one to two eV if it is connected. Stronger substitution implies stronger connected shifts, but weaker shifts and weaker alternancy of intensity for unconnected carbons, leading to an enhanced benzene-like building-block feature of the shake spectrum. The first strong feature of the substituent spectra are also benzene-like.