The predicted spectrum of FeOH in its Renner-degenerate X∼6A′ and A∼6A″ electronic states

FeOH is an iron-containing molecule that is a candidate for detection in interstellar space. It has not yet been spectroscopically characterized and we simulate the microwave and infrared spectra to assist in its discovery. At linearity the ground electronic state of FeOH is an orbitally degenerate 6Δ Renner state which, at bent configurations, splits into the electronic ground state X∼6Ai′ and the excited state A∼6Ai″. We have calculated the three-dimensional potential energy surfaces 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 together with associated electric dipole moment and transition dipole moment surfaces at the corresponding MR-SDCI/[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 Å, re(O-H) = 0.952 Å, 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 second excited electronic state (B∼6A′ correlating with 6Π at linearity) is located about 3740 cm−1 above the X∼ and A∼ states. We have carried out variational RENNER calculations, using our potential energy and dipole moment surfaces, in order to determine rovibronic term values and to simulate the microwave and infrared spectra that arise from transitions within and between these electronic states.