Gas-phase structures of acetyl peroxynitrate and trifluoroacetyl peroxynitrate

The molecular structures and conformational properties of acetyl peroxynitr ate (PAN, CH3C(O)OONO2) and trifluoroacetyl peroxynitrate (FPAN, CF3C(O)OON O2) were investigated in the gas phase by electron diffraction (GED), micro wave spectroscopy (MW), and quantum chemical methods (HF/3-21G*, KF/6-31G*, MP2/6-31G*, B3PW91/6-31G*, and B3PW91/6-311+G*). All experimental and theo retical methods show the syn conformer (C=O bond of acetyl group syn to O-O bond) to be strongly predominant relative to the anti conformer. The O-NO2 bonds are extremely long, 1.492(7) Angstrom in PAN and 1.526(10) Angstrom in FPAN, which correlates with their low bond energy and the easy formation of CX3C(O)OO. and (NO2)-N-. radicals in the atmosphere. The O-O bonds (1.4 18(12) Angstrom in PAN and 1.408(8) Angstrom in FPAN) are shorter than that in hydrogen peroxide (1.463 Angstrom). In both compounds the C-O-O-N dihed ral angle is close to 85 degrees.