ANGELIKA HERMANN, JAN NIEMEYER, HANS-GEORG MACK, DINES CHRISTEN AND HEINZ OBERHAMMER, Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany; HELGE WILLNER, Institute of Synthetic Chemistry, University of Duisburg, Germany; MARTIN SCHÄFER AND ALFRED BAUDER, Laboratory of Physical Chemistry, ETH, Zürich, Switzerland.

The molecular structure and conformational properties of trifluoroacetyl peroxynitrate, FPAN, CF3C(O)OONO2, were investigated in the gas phase by electron diffraction, microwave spectroscopy and quantum chemical methods. All experimental and theoretical methods show the syn conformer (C=O bond of the acetyl group syn to O-O bond) to be strongly predominant relative to the anti conformer. The O-N bond is extremely long (1.526 (10) Å ), which correlates with the low bond energy and the easy formation of CF3C(O)OO and NO2 radicals in the atmosphere. The O-O bond (1.408 (8) Å ) is shorter than that in hydrogen peroxide (1.464 Å ) and the C-O-O-N dihedral angle is close to 85o.