Properties of Pure Nitryl Bromide. Thermal Behavior, UV/Vis and FTIR Spectra, and Photoisomerisation to trans-BrONO in an Argon Matrix

Abstract

BrNO₂ is produced by the heterogeneous reaction of ClNO₂, highly diluted in He, with an aqueous bromide solution and subsequent trapping at -155 °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 Br₂ 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 ClNO₂ 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 XNO₂ and XONO (X = Cl, F).