Many-body calculations on molecules with second-row atoms: H₂S and H₂CS

The ionization potentials of H₂S and H₂CS are calculated by a many-body Green's function method. Correlation energy changes in the diffuse part of the charge cloud require an extension of the polarization function basis compared to the first row atoms. When f-type functions are included all calculated ionization potentials of H₂S agree with the experimental values to within 0.1 eV. The ionization potentials of H ₂CS agree satisfactorily with the recently determined experimental values except for the fourth band where possibly predissociation occurs. The ordering of the ionic states is the same for H₂CS as for H ₂CO. The vibrational structure in the photoelectron spectrum of H₂CS is computed.