A discharge flow apparatus with chemiluminescence detector has been used to study the reaction O+ClO→Cl+O2*, where O2*=O2(a2Δg) or O2(b1&Sgr;+g). The measured quantum yields for producing O2(a1Δg) and O2(b1&Sgr;+g) in the above reaction are less than 2.5¿10-2 and equal to (4.4¿1.1)¿10-4, respectively. The observed O2(a1Δg) airglow of Venus cannot be explained in the context of standard photochemistry using our experimental results and those reported in recent literature. The possibility of an alternative source of O atoms derived from SO2 photolysis in the mesosphere of Venus is suggested. ¿ American Geophysical Union 1987