Knowledge Bank

Spectroscopic constants and energy levels of the ground and low-lying excited states of iron carbide, FeC, have been calculated from potential energy functions obtained by the ab initio MR-SDCI molecular orbital approach. Investigated states are $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Delta$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\Pi$, both of which are proposed by DF $spectraa$ as a candidate for the new $\Omega =2$ electronic state observed above the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Delta 2$ state by $3460cm-1$. The character of each electronic state has been discussed theoretically. Contrary to the previous tentative assignment to $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\Pi$, the MR-SDCI results predict that the observed $\Omega =2$ state should be the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Delta$ state and be located at $3252cm-1$ above $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Delta 2$. The spin-orbit coupling constant for $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Delta$ state has also been calculated.