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

Abstract

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.