Electronic spectrum of AuF: Hyperfine structure of the [17.7]1 state

The [17.7]1-X¹Σ⁺ (0,0) band of AuF at 566 nm has been studied by laser excitation spectroscopy. The molecule was prepared in a dc electric discharge by flowing a dilute mixture of SF₆ in argon through a hollow gold cathode. The rotational structure of the band has been analyzed for the first time, yielding accurate values for the rotational and Ω-type doubling constants of the upper state. Hyperfine splittings arising from both the ¹⁹⁷Au and ¹⁹F nuclei have been resolved by recording the spectrum at sub-Doppler resolution using the technique of intermodulated fluorescence spectroscopy. The hyperfine structure is dominated by the ¹⁹⁷Au magnetic dipole interaction in the [17.7]1 state, with the ¹⁹⁷Au magnetic hyperfine constant determined to be h₁ =-543(4) MHz. It is demonstrated that the negative value of this constant implies that the [17.7]1 state has significant ³Δ₁ character and that spin-orbit mixing with a ¹π₁ state may be providing the transition intensity to the ground electronic state.