The infrared electronic spectrum of FeO

The near-infrared electronic system of FeO has been recorded in emission at high resolution with the 1-meter FT spectrometer at Kitt Peak National Observatory. The system has been found to consist of two overlapping band systems lying in the region 7 000 - 14 000 cm⁻¹. These share a common lower state and this is the same lower state as that of the orange system. This state, which has vibrational constants (in cm⁻¹) ω[sub e] = 880.4148, ω[sub e]x[sub e] = 4.632 15, and ω[sub e]y[sub e] = 5.55 x 10⁻⁴ has been established as the ground state of the molecule by the matrix isolation experiments of Green, Reedy, and Kay (J. Mol. Spectrosc. 1979, 78, 257-266) and has been identified as a⁵Δ[sub i] state in earlier studies done in this laboratory on the orange system. The present work has proven this identity, and least-squares data reduction has yielded the ground state constants: B[sub e] = 0.518 721 cm⁻¹, α [sub e] = 0.003 825 cm⁻¹, τ [sub e] = -4.8x10⁻⁷ cm⁻¹, D[sub e] = 7.210 x 10⁻⁷ cm⁻¹, β[sub e] = 1.51 x 10⁻⁹ cm⁻¹, r[sub e] = 0.161 64 nm, and A = -94.9 cm⁻¹. These were based on combined data from the infrared and orange systems for the levels v = 0-3, together with six microwave frequencies obtained by Endo. Saito, and Hirota (Ap. J. 1984, 278, L131-L132). Both the ⁵Δ₀ and ⁵Δ₁, substates are found to show small A-doublings, with that in ⁵Δ₀ being the larger (~0.3 cm⁻¹). In contrast to all the known excited states of FeO, the ground state is well-behaved, but even this state possesses one small rotational perturbation. This is observed only in one parity component of the J = 15 level of the v = 2 level of the X⁵Δ₂ substate and is probably caused by the low-lying ⁷Σ state predicted by Krauss and Stevens (J. Chem. Phys. 1985, 82, 5584-5596). The upper level of the infrared system consists of two overlapping states about 10 200 cm⁻¹ above the ground state and separated by only about 213 cm⁻¹ at their v = 0 levels. The upper of these, a ⁵π[sub i] state, has the approximate values Δ G[sub ½] ≃ 627 cm⁻¹ and A[sub O] ≃ -217 cm⁻¹ and for the lower ⁵Φ[sub i] state Δ G[sub ½] ≃ 593 cm⁻¹ and A[sub O] ≃ -47 cm⁻¹. These are very rough estimates only, as a result of the vast number of rotational perturbations present. Effective rotational constants for the individual substates have been determined rather than a global set of constants, again because of the perturbations. Amongst the perturbing states, at least one multiple Σ state is present and there may be as many as three. Evidence is also presented for the existence of a ³Φ state.Science, Faculty ofChemistry, Department ofGraduat