Observation and identification of the g 6Φ–a 6Δ transition in the blue system of FeH at 493 nm

Abstract

The blue system of FeH, at 493 nm, has been recorded with a sample at near‐ambient temperatures by laser excitation spectroscopy. With the help of dispersed fluorescence studies, all the strong lines in this region of the spectrum have been assigned to the (0,0) band of the g ⁶Φ–a ⁶Δ transition, where the lower state lies about 1890 cm⁻¹ above the ground ⁴Δ state. Assignments have been made to ΔΩ=+1 and ΔΩ=0 subbands involving the lowest three spin components in each state. Term values have been determined for the levels of the three lowest spin components of the a ⁶Δ state and thereby for the g ⁶Φ_11/2 spin component, which were hitherto unknown. It is established that the a ⁶Δ state of FeH is inverted and that the vibrational interval ΔG_1/2 varies markedly between the spin components of this state: ⁶Δ_Ω 9/2 7/2 5/2 ΔG_1/2/cm⁻¹ 1622 1569 1582. There is evidence that the a ⁶Δ state is perturbed by levels of other, nearby electronic states and it is not possible to model its levels with a simple effective Hamiltonian. The radiative lifetime of FeH in the two lowest spin components of the g ⁶Φ state has been measured as 39±2 ns.