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).
The synthesis of FC(O)OONO2 is accomplished
by the photolysis of a mixture of (FCO)2, NO2,
and O2. The
pure product is isolated after trap-to-trap condensation and the
removal of byproducts by treatment of the crude
product with O3 and AsF5. The colorless
liquid freezes at −105 °C; its boiling point is 32 °C. At 20
°C and a
few millibars, FC(O)OONO2 decomposes in the gas
phase with a half-life of 20 h. FC(O)OONO2
is characterized
by vapor pressure measurements, vibrational, 19F NMR,
13C NMR and UV spectroscopies as well as by
mass
spectrometry. According to the vibrational and NMR spectra, the
compound exists at room temperature only as
a syn conformer. The molecular structure of
FC(O)OONO2 is determined by gas electron
diffraction. The molecule
possesses a skew structure with a dihedral angle of φ(COON) =
86.2(14)°. The short O−O bond (1.420(6)
Å)
and the long N−O bond (1.514(6) Å) are consistent with the
chemical properties of this compound. The
experimental geometry is reproduced reasonably well by quantum
chemical.
Ozone is formed in good yield by reacting O2
+ salts with water in HF at −78 °C. With isotopically
labeled water 17O−16O−16O and 18O−16O−16O can be prepared, and other isotopomers could be made by
starting with 17O2
+ and 18O2
+ precursors. 17O NMR spectroscopy and IR matrix spectroscopy are used for
detection and decay of the isotopomers. The 17O or 18O label at the terminal position remains at −78 °C, but
at higher temperatures scrambling of the atoms is observed. Under strict monomolecular conditions no
scrambling is observed till 450 °C, however. Irradiation of ozone in a 15K argon matrix with λ = 254 nm
affords scrambling of the label and formation of oxygen. Irradiation with λ > 420 nm initiates only scrambling
with little decay. The possible mechanisms of the atomic scrambling are discussed.
The gas phase reaction between BrNO and O(3) at low pressure (<10 mbar) results in the formation of BrNO(2) in about 60% yield. In this manner (15)N- and (18)O-labeled BrNO(2) are prepared. In addition, it is shown that BrNO(2) also forms by the heterogeneous low-temperature reaction between gaseous BrNO and solid sulfuric acid, doped with H(2)O(2). It can be assumed that BrNO(2) may be formed in a similar way under stratospheric conditions. The isotope scrambling in the reaction between BrNO and (18)O(3) as well as in the gas phase equilibrium BrNO + NO(2) right harpoon over left harpoon BrNO(2) + NO are investigated. For the equilibrium constant a lower limit of K(298) >/= 1 x 10(-)(3) is deduced from infrared measurements. A detailed IR and Raman study on BrNO(2) is performed. Photolysis of matrix-isolated BrNO(2) at different wavelengths leads to a mixture of cis- and trans-BrONO. The vibrational data of BrNO(2) (6 fundamentals, 7 combinations), cis-BrONO (5 fundamentals, 1 overtone), and trans-BrONO (4 fundamentals, 8 combinations) as well as the calculated force fields are in excellent agreement with the ab initio values, predicted by T. J. Lee (J. Phys. Chem. 1996, 100, 19847).
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