Gaseous chlorine perchlorate, ClOClO3, is found to be a major photolysis product of chlorine dioxide (OClO). Experiments were performed at room temperature with both continuous wave (mercury lamp) and pulsed (XeCl UV laser) light sources. The technique of time-resolved IR spectral photography (TRISP) was used to monitor the growth of the strong 1282-cm-1 ClOClO3 IR band following the application of a single ∼35 ns long, ∼70 mJ/cm2, XeCl laser pulse to a mixture of ∼30 torr of OClO and ∼700 torr of N2. It was found that under these conditions this band forms with a time constant of ∼1 μs. A transient IR band of unknown origin at ∼1232 cm-1 was also observed to develop on the same time scale. © 1982 American Chemical Society.