The effect of the Gaunt interaction on the molecular ionization spectra of CO, H2S and TlH

In this work we calculate the outer valence ionization spectra of the CO, H2S and TlH molecules by application of the recently developed Dirac-Hartree-Fock one-particle propagator technique. The molecules hereby serve as representatives of light and heavy systems and the influence of the Gaunt term on the spectral structure is investigated. The Gaunt term is a first correction to the non-covariant Coulomb repulsion term and has a considerable effect on the electronic ground state energy and also affects properties mainly determined by the inner-core region of the wavefunction where the electrons are fast. In order to reveal a possible influence of the Gaunt correction on the valence photoelectron (PE) spectra of heavy systems a consistent theoretical description of electron correlation and relativity is necessary. It was observed that the Gaunt correction plays only a minor role for the valence PE spectra even in heavy systems such as TlH and can safely be neglected