The FTIR- and UV-spectra of OBrO have been measured in solid argon matrices at 17 and 4 K. All three fundamentals of OBrO could be observed. The previously unknown frequency of the bending vibration (ν 2 ) was located at 317.0 cm - 1 /316.3 cm - 1 for 1 6 O 7 9 Br 1 6 O/ 1 6 O 8 1 Br 1 6 O and at 302.1 cm - 1 /301.4 cm - 1 for 1 8 O 7 9 Br 1 8 O/ 1 8 O 8 1 Br 1 8 O. OBrO was synthesised by photoisomerising BrOO at 275 nm. The BrOO/argon matrix was prepared by adding bromine atoms from a discharge flow system to molecular oxygen on the surface of a growing argon matrix. We show that the photoisomerisation of BrOO to OBrO is reversible. In addition, the wavelength dependency of the OBrO and BrOO photochemistry in argon matrices and the isomerisation rate has been determined in the wavelength range 200-600 nm.