The UV–Vis Spectrum of the ClCO Radical in the Catalytic Cycle of the Cl-Initiated CO Oxidation

In the Venus mesosphere, the observation/model discrepancy of oxygen abundance has been a long-standing puzzle. Chlorine atoms have been proposed as a catalyst for the oxidation of carbon monoxide through the formation of chloroformyl radicals (ClCO), removing O2 through formation of ClC(O)OO and ultimately generating CO2. However, relevant chemical kinetic studies are scarce and are highly uncertain. In this work, we report the spectrum of the ClCO radical between 210 – 520 nm using a multipass UV–Vis spectrometer coupled to a pulsed-laser photolysis flow reactor at 236 – 294 K and a pressure of 50  491 Torr. High-level ab initio calculations were performed to simulate the observed spectrum and explored the electronic structure. The observed pressure effect on Cl2 regeneration and Cl2CO formation revealed that both the terminal Cl atom and the central C atom are the reactive center in the ClCO radical. Most importantly, the reported spectrum will enable measurements of key kinetic parameters related to the fate of ClCO, which are important for the chemistry of the Venus mesosphere.