Visible, near-infrared and mid-infrared spectra of solid O₂at 6-33 K

We report spectra in the visible and near-infrared wavelength range 350-1155 nm and in the mid-infrared range 500-5000 cm-1 (2-20 μm) of molecular oxygen at temperatures 6-33 K. In mid-infrared spectra, a sharp line at 1552.4 cm-1 was observed at a deposition temperature of 6 K. The intensity, profile and position of this feature depended sensitively upon the deposition temperature as a result of a connection with lattice imperfections; instead, a triplet feature at 1545.7, 1548.1 and 1549.6 cm-1 appeared at temperatures 9 and 12 K, but disappeared at 18, 24 and 30 K. Additional infrared lines of solid α-O2 were observed at 1591 and 1617 cm-1, which exhibited a reversible behaviour through the α-β phase transition temperature at 24 K. The transmissions of solid O2 showed nearly no change in wavenumber range 500-2000 cm-1 (5-20 μm) at temperatures 6-33 K; above 2000 cm-1 (<5 μm), the transmission of solid O2 depended strongly on temperature. Roughly, the transmission of solid O2 at temperatures 6-21 K fluctuated slightly in the visible and near-infrared region, whereas it decreased greatly at 24 K and continuously diminished further at higher temperatures. Notably, a broad absorption of solid β-O2 was observed in the wavelength region 350-700 nm at temperatures 27, 30 and 33 K.