Infrared spectra of gaseous peroxychloroformyl radical ClC(O)OO: A key intermediate in the conversion of CO to CO2 in the Venus atmosphere

The peroxychloroformyl radical, ClC(O)OO, was proposed to play a critical role in the catalytic conversion of CO to CO₂ in the atmosphere of Venus, but direct spectral characterization of this species in the gaseous phase is lacking. Photolysis of a mixture of (ClCO)₂ and O₂ near 50 Torr with laser light at 248 nm produced absorption bands of CO, CO₂, Cl₂CO, and transient absorption bands that can be assigned to ClCO, trans-ClC(O)OO, and cis-ClC(O)OO. Bands at 937, 1014, and 1902 cm⁻¹ are assigned to the OCO bending (ν₃), overtone of C−Cl stretching (2ν₅), and C=O stretching (ν₁) modes of trans-ClC(O)OO. According to rotational contour simulations with PGOPHER, two bands ∼ 1883 and ∼ 1928 cm⁻¹ also contribute to the band near 1902 cm⁻¹; they might be assigned to the ν₂ + ν₈ + ν₉ mode of cis-ClC(O)OO and the ν₂ + ν₄ mode of trans-ClC(O)OO, whereas the band near 937 cm⁻¹ might have contribution from the 2ν₆ (overtone of OC=O bending) mode of cis-ClC(O)OO near 928 cm⁻¹. Bands at 964, 1110, and 1837 cm⁻¹ are assigned to the anti-phase C–O and O–O stretching (ν₃), O–O stretching (ν₂), and C=O stretching (ν₁) modes of cis-ClC(O)OO. The band near 1837 cm⁻¹ might have contribution from the 2ν₃ mode of trans-ClC(O)OO and cis-ClC(O)OO near 1829 and < 1829 cm⁻¹, respectively. From the temporal evolution of CO and CO₂, we confirmed that the addition of O₂ to the photolyzed (ClCO)₂ system to form ClC(O)OO enhanced the formation of CO₂, supporting the proposed catalytic mechanism.