Clt2p–photoelectron spectrum of HCl studied by fully relativistic, self-consistent-field, and configuration-interaction calculations

Abstract

Fully relativistic, all-electron self-consistent-field calculations, based on the Dirac-Coulomb͑-Gaunt͒ 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 -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.

Theory and ab initio calculations of 2p photoabsorption spectra: The lowest Rydberg resonances in HCl

“…In prior theoretical work, the electronic structure of the core ionized HCl was investigated by Ellingsen et al with a fully relativistic configuration interaction ͑CI͒ approach 13 and by the present authors 23 with the partially empirical approach of Bo "rve et al 11 Both approaches gave very similar results for the nature of the core ionized states and for their energies. In the latter article, furthermore, the dominant process following core ionization, the Auger decay, was investigated.…”

“…͑1͒ In the core ionization, which was discussed in detail before, [10][11][12][13]23 the relativistic wave function is set up only from nonrelativistic doublet states, which differ in energy due to the molecular field effects on the core orbital. For the core excitation considered here, the relativistic wave function is, due to the spin-orbit interaction, a strong mixture of singlet and triplet states.…”

“…The quality of the calculated excitation energies may be judged from the average Cl 2p ionization potential ͑IP͒ 207.88 eV that should be compared to the experimental value of 207.95Ϯ0.05 eV. 13 As discussed in our prior publication, 23 the calculated IP will probably increase if the basis set is further improved, but inclusion of zero-point vibrational effects reduces it by about 0.03 eV. We estimate the errors of the calculation in the core excitation energies to approximately 0.1 eV and the errors of the relative energies to about 0.05 eV.…”

“…H 2 S, 10 SO 2 , 11,12 and HCl. 13 The energetic structure of the core hole states is then mainly determined by the spin-orbit splitting of the core shell and by the molecular field which lifts the degeneracy between the 2lϩ1 components of the shell. Recently, Bo "rve 11 has shown that very accurate values for the energy levels of such core ionized states can be obtained, if the spin-orbit coupling is treated only in the shell of the core hole by a partially empirical Hamiltonian and the molecular field splitting is accounted for by accurate ab initio calculations.…”

Linear Dichroism in Resonant Inelastic X-Ray Scattering to Molecular Spin-Orbit States

“…Recently, high-resolution core-level-photoemission measurements (ÁE $ 40 meV) identified contributions from three SO sublevels, 2 Å 1=2 , 2 AE 3=2 , and 2 Å 3=2 , in L-edge photoionization of HCl, arising from coupling between MF and SO interactions in the ionized molecule [1,2]. Other examples also have shown high-resolution photoelectron spectra [3], as well as spin-resolved photoemission [4], can be sensitive probes of molecular environments in ionized species.…”