Molecular field and spin–orbit splittings in the 2p ionization of second-row elements: a Breit–Pauli approximation applied to OCS, SO2, and PF3

An ab initio Breit–Pauli (BP) approach is applied for 2p ionized states, 2P3/2 and 2P1/2, of OCS, SO2, and PF3. Diagonal elements in the BP spin–orbit Hamiltonian matrix over six 2p−1 hole configurations are corrected by using non-relativistic 2p hole-state energies based on configuration interaction (CI) with single and double substitutions from reference states with five electrons in the 2p manifold, (2p)5-SDCI. The molecular field splitting in the 2P3/2 state is sensitive to geometric relaxation in the core hole state, and the spin–orbit splitting is sensitive to relaxation in the 2p orbital itself. The spin–orbit wavefunction is characterized in terms of σ and π-type chemical bonds.