High-resolution spectroscopy of the a⁴Σ⁻_3/2 − X₁²Π_3/2 system of gold monosulphide in the near infrared

We have recorded the a4Σ− 3/2 − X1 2Π3/2 (0,0), (1,0), and (2,0) bands of gaseous gold monosulphide (AuS) at sub-Doppler resolution in the near-infrared region. The molecules were made in a hollow cathode discharge source by the reaction of sputtered gold with carbonyl sulphide. The high resolution of the laser excitation spectrum enabled the determination of molecular constants describing the rotational and 197Au hyperfine structure in both states, as well as the spin–rotation interaction in the a4Σ− 3/2 state. The natures of the two electronic states are discussed in the context of the observed hyperfine structure.