Rotational and hyperfine structure in the A4Δ – X4Φ, B4Γ – X4Φ and C4Δ – X4Φ transitions of ruthenium monofluoride (RuF)

Laser Induced Fluorescence (LIF) has been used to study the spectroscopy of ruthenium monofluoride (RuF) in the UNB laser-ablation molecular-jet apparatus. High-resolution spectra of three band systems have been obtained, with a linewidth (FWHM) of ∼0.004 cm⁻¹, in the near infrared (NIR), green and blue regions at ∼ 760 nm, 548 nm and 450 nm respectively. Electronic states have been assigned based on observation of first lines in the R and P branches and the excited states are labelled A, B and C in increasing energy order. Three transitions have been assigned to the green system as spin–orbit components, B⁴Γ_5.5 – X⁴Φ_4.5 and B⁴Γ_4.5 – X⁴Φ_3.5 of the (0,0) band, and B⁴Γ_5.5 – X⁴Φ_4.5 of the (1,1) band of the B – X system. The single NIR and blue bands were assigned as A⁴Δ_3.5 - X⁴Φ_4.5 (0,0) and C⁴Δ_3.5 - X⁴Φ_4.5 (0,0) respectively. Rotational structure of four individual isotopologues ⁹⁶RuF, ¹⁰⁰RuF, ¹⁰²RuF and ¹⁰⁴RuF was well resolved and used to examine the rotational and vibrational isotope effects. The rotational lines were doubled by hyperfine structure due to the nuclear spin I = ½ of fluorine. The hyperfine structure due to the nuclear spin I = 5/2 of ⁹⁹Ru and ¹⁰¹Ru was not resolved resulting in weak broadened ⁹⁹RuF and ¹⁰¹RuF lines that were overlapped by the stronger lines of the other isotopologues and could only be assigned in the C⁴Δ_3.5 - X⁴Φ_4.5 (0,0) band. The fluorine hyperfine structure was used to estimate the fraction of F 2sσ and 2pπ in the Ru-centered σ and π molecular orbitals.