Visible and infrared spectra of the solids α- And β-O₂ at 9–30 K

To establish the spectroscopy of the solids α- and β-oxygen, we measured the thermal ramping spectra of the solid O₂ in visible and near-infrared (near-IR) wavelength range 450–1020 nm and mid-infrared (mid-IR) range 500–5000 cm⁻¹ (2–20 μm) at temperature 9–30 K. Besides the solids α- and β-oxygen, the imperfect structure of O₂ ice might co-exist at low temperature. In mid-IR spectra, a triplet was observed at 1545.7, 1548.1, and 1549.6 cm⁻¹ associated to the imperfect crystallinity of solid O₂; the triplet existed below 27 K, but not at 30 K and on re-cooling to 9 K. The spectra measured at re-cooled 9 and 30 K are evidently responsible only for the solids α- and β-O₂, respectively; overall, the spectra of the solids α- and β-O₂ appear similar in the visible region, but those differ significantly from the spectrum of the solid O₂ contaminated with imperfect structure. For solid α-O₂, IR lines were recorded at 1591 and 1617 cm⁻¹, which exhibited a reversible behaviour through the α-β phase transition temperature at 24 K. The visible spectrum of the separate solid α-O₂ was obtained for the first time.