Cl 2p-photoelectron spectrum of HCl studied by fully relativistic, self-consistent-field, and configuration-interaction calculations

Fully relativistic, all-electron self-consistent-held calculations, based on the Dirac-Coulomb(-Gaunt) Hamiltonian, have been performed on the ground state and the three Cl 2p-ionized states of HCl. The calculations are done by the Dirac-Fock method and correlation is included through relativistic configuration-interaction calculations. The core-orbitals of HCl are shown to have a relativistic character and a description of the Cl 2p-ionized states in terms of omega omega-coupling is found to be crucial. Calculated Cl 2p-ionization energies and energy splittings are in very good agreement with recent experimental, high resolution results. For the ionization energies, relaxation dominates correlation, and the effect of correlation are found to be neglible. Furthermore, the combined effects of the Gaunt term and core-valence correlation brings the calculated energy splittings in excellent agreement with experiment.