Measurement of the O2 (b1Σg+ → a1Δg) transition probability by the method of intracavity laser spectroscopy

The method of intracavity laser spectroscopy using a Co:MgF₂ laser is applied to record the absorption spectra from the first excited a¹Δ_g state of gaseous molecular oxygen at the a¹Δ_g → b¹Σ_g⁺ transition at 1.91 μm. The gas flow from a chemical singlet oxygen generator with a known concentration of singlet oxygen O₂ (a¹Δ_g) was supplied to the cavity of the Co:MgF₂ laser. The absorption line intensities are measured for five spectral lines of the Q-branch of the 0—0 vibrational band for the a¹Δ_g → b¹Σ_g⁺ transition. The O₂ (b¹Σ_g⁺ → a¹Δ_g) transition probability calculated from these data was (1.20 ± 0.25) × 10^-3 s^-1.