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

The [17.7]1-X(1)Sigma(+) (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 SF(6) 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 Omega-type doubling constants of the upper state. Hyperfine splittings arising from both the (197)Au and (19)F 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 (197)Au magnetic dipole interaction in the [17.7]1 state, with the (197)Au magnetic hyperfine constant determined to be h(1) = -543(4) MHz. It is demonstrated that the negative value of this constant implies that the [17.7]1 state has significant (3)Delta(1) character and that spin-orbit mixing with a (1)Pi(1) state may be providing the transition intensity to the ground electronic state.