Rydberg spectra of singlet metastable states of O₂

Updated analyses of several singlet Rydberg states of O₂ via spectra involving excitation from the metastable a¹Δ_g and (Formula presented.) states are presented. The high-quality FT-VUV spectra available from the DESIRS beamline at the SOLEIL synchrotron gives significantly improved spectra compared to previous work. The Rydberg states analysed include (Formula presented.) v = 0–4, 3pσ¹Π_u v = 0–2, 3pπ¹Δ_u v = 0–2, (Formula presented.) v = 0–1, 4pσ¹Π_u v = 0 and 4pπ¹Δ_u v = 0. This is complemented by high-quality ab initio calculations on the (Formula presented.) and ¹Δ_u Rydberg states to determine the transition moments providing the first quantitative cross-sections for Rydberg–(Formula presented.) transitions. These are validated against the experimental data. The results suggest the most promising candidate for determining (Formula presented.) number density is likely to be the 1–0 band of the (Formula presented.) transition at 131.3 nm.