Hyperfine Resolved Spectrum of the a⁴Σ^–_3/2–X²Π_3/2 System of Gaseous Gold Sulfide (AuS) in the Near Infrared

We have recorded the electronic spectrum of the a⁴Σ^–_3/2–X²Π_3/2 system of gold monosulfide (AuS) in the near infrared region. The molecules were produced by sputtering gold in a hollow cathode discharge source followed by reaction with carbonyl sulfide (OCS). We recorded initial scans at low resolution using a pulsed laser that revealed a vibrational progression from the (0,0) to (5,0) bands, covering the region from 821 to 721 nm. Many hot bands were also observed. Following this work, the (2,0), (1,0) and (0,0) bands were recorded, first at Doppler-limited and then at sub-Doppler resolution using a continuous-wave Titanium:Sapphire ring laser. The ground state of AuS is an inverted ²Π state with a spin-orbit splitting of 1318.5 cm^–1. From our least-squares fitting, we have determined accurate values for the vibrational, rotational and hyperfine parameters of the a⁴Σ^–_3/2 and X₁²Π_3/2 states.