Knowledge Bank

The electronic structure of FeO and RuO was calculated in a multi-configuration selfconsistent-field (MC-SCF) where three sigma, two pi, and one delta orbitals were considered as open valence orbitals and all configurations that arise from this space were optimized (complete active space (CAS)). Relativistic effective potentials (REP) were used to both simplify the integral and SCF calculations and to make the calculation of the spin-orbit interaction tractable. The calculated ground state spectroscopic constants for FeO are not in good agreement with experimental values but the values for the ground state of RuO are reasonable. The values for the $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\pi$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\varphi$ excited states of FeO are also in accord with experiment, and the calculated spin-orbit constants for these states support the assignment. The observation of different levels of accuracy for different states can be rationalized in terms of differential correlation effects. The CAS-MC-SCF results for FeH and RuH were obtained with an open valence space of four sigma, two pi, and one delta. For FeH the $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}\Delta$ is found lowest in energy at this level of calculation, which is not in accord with the experimental assignment. The $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Delta$ is a close-lying excited state for FeH, but is lower in energy than the $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}\Delta$ for RuH. However, as would be evident from the atomic level differences from Fe and Ru, the ground state of RuH is calculated to be a $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\varphi$ state. The electronic structure of the ground and low-lying excited states will be discussed as well as the effects of correlation on the structure. The electronic structure of the ground state of the negative ions as determined at this level of approximation will be noted.