Analysis of the microwave spectrum of the bis-trifluoromethyl nitroxide
White, Richard Michael
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The microwave spectrum of the stable free radical bis-trifluoromethyl nitroxide was analyzed in the 20 to 26.5 GHz region. 39 transitions have been assigned. The rigid rotor rotational constants determined by calculation of the hypothetical unsplit rotational transitions are A= 2256.94 MHz, B= 1056.08 MHz, and C=971.51 MHz. A program to calculate the fine and hyperfine splitting patterns was written which reproduced the experimentally observed splittings. The spin-rotation coupling constants are Eaa = -3597.7 MHz, Ebb= -1121.4 MHz, and Eee = 29.8 MHz. The magnitude of Eee indicates that the unpaired electron is in an orbital extending perpendicularly to the molecular plane. The determined magnetic hyperfme coupling constants are Taa= -183.74 MHz, Tbb= -177.77 MHz, Tee= 361.51 MHz, and aF= 22.8 MHz. The spin density on the fluorine atom is 11.9% which is estimated from the value of Tee· The value of the Fermi coupling constant aF indicates that the unpaired electron occupies an unhybridized p orbital. An insufficient number of unsplit rotational transitions were assigned to allow a centrifugal distortion analysis to be performed. Since isotopic substitution was not feasible an r0 structure was determined by doing a least squares fit of the three moments of inertia. The following parameters were not allowed to vary during the least squares fit: reF= 1.32A,rcN= 1.441A, F - C - F = 109.8° . The calculated structure gave a N-0 bond length of 1.212A ,a C-N-0 angle of 116.9° a C-N-C ·angle of 126.2° , and an angle which measures the deviation of the 0 atom from the CNC plane of 0° .
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