Properties of pure nitryl bromide. Thermal behavior, UV/Vs and FTIR spectra, and photoisomerization to trans-BrONO in an argon matrix

BrNO2 is produced by the heterogeneous reaction of CINO2, highly diluted in He, with an aqueous bromide solution and subsequent trapping at -155 degrees C. The crude product is purified by trap to trap condensation and fractional sublimation in vacuo. At 300 K and a pressure of 1 mbar, a half-life of about 1 h is observed. The decomposition produces Br-2 and NO2. The UV/vis and IR absorption cross sections of gaseous BrNO2 are determined in the ranges 185-600 nm and 2000-400 cm(-1), respectively. Irradiation of matrix-isolated BrNO2 with visible light causes nearly quantitative isomerization to trans-BrONO, while CINO2 is converted by UV light into a mixture of cis- and trans-ClONO. It is possible to assign all fundamentals of BrNO2 and trans-BrONO by comparison to the respective band position of the analogous molecules XNO(2) and XONO(X=Cl, F).