Photoionization of the primary photofragments of chlorine dioxide (OClO) and dichlorine monoxide (Cl₂O) is reported. The nascent photofragments are formed by UV photolysis, they are subsequently photoionized by time-correlated XUV laser radiation and finally detected by time-of-flight mass spectrometry. Primary photolysis of OClO leads to the formation of ClO+O at λ=359.5 nm, whereas ClO+Cl are formed by photolysis of Cl₂O at λ=250 nm. The XUV photoionization of the photolysis products relies on single photon ionization. This allows to derive partial photoionization cross sections of the parent cations and their photolysis products from mass spectral intensities by using the absolute photoionization cross sections of the atomic products for calibration. Specifically, we obtain for OClO at E=13.74 eV: σ_ClO=27±5 Mb and σ_OClO=18.5±3 Mb. Consistent findings are obtained from equivalent experiments on Cl₂O. The present results are compared with previous photoionization work on ClO and OClO to demonstrate the reliability of UV-pump/XUV-probe spectroscopy.