10min:

J. ORPHAL, Institute of Environmental Physics, University of Bremen, P. O. Box 330440, 28334 Bremen, Germany; B. REDLICH, H. GROTHE AND H. WILLNER, Institute of Physical Chemistry, University of Hannover, Callinstr. 9, 30167 Hannover, Germany; A. FRENZEL AND C. ZETZSCH, Fraunhofer-Institute of Toxicology and Aerosol Research, Fuchsstr. 1, 30625 Hannover, Germany.

Nitryl bromide (BrNO₂) formed by heterogeneous reactions on polar stratospheric clouds and on sea-salt particles in the marine troposphere. However, no rotationally resolved spectra have been reported up to now, and nothing is known about rotational constants, structure, and force field of BrNO₂. In fact, the only observations of BrNO₂ in the gas phase were possible using flow experiments with gaseous N₂O₅ flowing over NaBr particles.

In this study, a different approach was used: By reaction of highly diluted gaseous ClNO₂ with an aqueous Br^- solution, BrNO₂ was formed and trapped at low temperature. The crude product was purified by trap-to-trap condensations and fractional sublimation in vacuo.

High-resolution infrared spectra of the ₄ band of BrNO₂ around 1660 cm^-1 were measured with resolutions of up to 0.002 cm^-1, using the Bruker IFS-120HR FTS at University of Hannover. For the first time, rotational constants for the ⁷⁹BrNO₂ and ⁸¹BrNO₂ isotopomers were determined for the ₄ and ground vibrational states. The constants were used for determination of a first substitution structure and, together with infrared band centers, the harmonic force field of BrNO₂.