HOOClO2 was produced by addition of hydrogen atoms to a mixture of O-2 and OClO on the surface of growing argon matrixes at 17 K. The compound was identified by infrared spectroscopy utilizing the H to D and O-18(2) and O-16,18(2) spectral shifts. The matrices were irradiated with the full radiation from a 300-W Xe lamp. HOOClO2 was eliminated by the irradiation, but we were unable to identify the photodecomposition product. Ab initio calculations show that HOO binds to OClO with a bond strength intermediate between a van der Waals interaction and a covalent bond.