Equivalent core-hole time-dependent density functional theory calculations of carbon 1s shake-up states of phthalocyanine

The shake-up transition energies of the carbon $1s$ photoelectron spectrum of metal-free phthalocyanine (H₂Pc) have been calculated by means of time-dependent density functional theory, for which an equivalent core approximation is adopted. Model calculations for the C0.2em0ex1s shake-up states of benzene are in excellent agreement with the latest experimental results. The complex C0.2em0ex1s shake-up structures associated with the aromatic and pyrrole carbons in the phthalocyanine are computed, as well as their ionization potentials. They allow us to determine the origin of the anomalous intensity ratio between the pyrrole and benzene carbons in a high resolution C0.2em0ex1s photoelectron spectrum measured for a H₂Pc film, as due to a benzene-related shake-up contribution, hidden under the pyrrole main intensity feature.