UV photolysis of H2O2 in solid Ar, Kr, and Xe yields isolated OH radicals and a complex between a water molecule and a ground-state (P-3) oxygen atom. The vibrational bands of the HOH ... O complex are observed at 3730.1 and 3633.0 cm(-1) in Ar, at 3718.6 and 3622.4 cm(-1) in Kr, and at 3704.3 and 3607.3 cm(-1) in Xe matrices. The assignment is based on isotopic substitution, selective photoinduced processes between H2O2 and HOH ... O, and ab initio calculations. In Kr and Xe matrices, the complex is formed with much less efficiency when compared with Ar matrices, indicating the existence of other photolysis channels. Computational results on the complex geometry and vibrational frequencies are presented and compared with experimental data.