Electronic structures and rovibronically averaged geometries of the X̃ A6i′ and à A6i″ states of FeOH

We have recently reported a theoretical prediction of the rovibronic spectra of the FeOH molecule. These spectra have not been observed experimentally. In the present work, we complement the previously published information by reporting the details of the electronic structure of FeOH together with rovibrationally averaged structural parameters. The electronic ground state is X A6i′, which is Renner-degenerate with the A A6i″ state; the two states correlate with a Δ6 state at linearity. We have calculated the three-dimensional potential energy surfaces (PESs) of the X and A states, which are close in energy over the range of geometries studied, at the MR-SDCI+Q+Erel/[Roos ANO (Fe), aug-cc-pVQZ (O, H)] level of theory. The equilibrium structure of the X state is bent with re(Fe–O)=1.806 A, re(O–H)=0.952 A, and ∠e(Fe–O–H)=134.2°. The barrier to linearity is 273 (266) cm−1 in the X (A) state so that FeOH is quasilinear in the X and A states. The Fe–O bonds in both states are ionic and the bending pot...