Direct detection of singlet oxygen O2(a1 Δg) by absorption at the a1 Δg → b1 Σg+ transition using intracavity laser spectroscopy

The absorption spectrum of singlet oxygen O₂(a¹ Δ_g) is detected in a gas phase at the a¹ Δ_g → b¹ Σ_g⁺ transition by the method of intracavity laser spectroscopy using a broad-band Co : MgF₂ laser emitting 200-μs pulses at a wavelength 1.91 μm. In the case of Doppler broadening of absorption lines at room temperature, the sensitivity of detection of O₂ (a¹ Δ_g) is ~ (2 – 5) × 10¹⁴ cm^-3 . It is shown that the gas temperature can be calculated from the dependence of absorption cross sections for individual lines on the rotational quantum number.