Knowledge Bank

The ground state of CoH has been determined experimentally as the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Phi$ by the far-infrared magnetic resonance $study,a$ and theoretically by ab initio $methods.b$ However, MR-SDCI and $MR-SDCI+Q$ ab initio molecular orbital calculations predicted that the lowest electronic state is $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\Phi$. The size-consistent MR-ACPF method correctly predicted that $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Phi$ should be the ground state. As is previously reported by Tanaka $etal.c$ on FeH, the controversial results in MR-SDCI may arise through truncation error inherent in the size-inconsistent MR-SDCI method. Another difficulty is that we cannot clearly separate the $\Phi$ and $\Pi$ states when CoH is treated under $C2v$ symmetry, not under its real symmetry of $C\infty v$. The best results we obtained at the moment are: $re=1.528\backslash AA$, $Be=7.291cm-1$, and $\omega e=2005cm-1$ at the level of the MR-ACPF + relativistic correction using the Roos ANO (Co) and Dunning aug-cc-pVQZ (H) basis sets.