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Published November 1951 | Published
Journal Article Open

The Structure of Trifluoromethyl Acetylene from the Microwave Spectrum and Electron Diffraction Pattern


Measurements, in the microwave region, of the J = 3→4 rotational transitions of trifluoromethyl acetylene and several of its isotopic modifications have been made, and the moments of inertia, I_B (in a.m.u.‐Å 2), have been found for the ground vibrational state: for CF_3CCH, 175.61_3, CF_3C^(13)CH, 177.02_4, CF_3CC^(13)H, 181.30_2, and for CF_3CCD, 187.46_2. Three lines corresponding to J = 3→4 transitions of CF_3CCH in the excited vibrational state v_(10) = 1, and two lines corresponding to v_(10) = 2 and v_(10) = 3, have also been measured and interpreted according to Nielson's theory of l‐type doubling in symmetric tops. From Stark effect measurements at different electric field strengths the dipole moment of CF_3CCH in the ground vibrational state has been found to be 2.36±0.04 Debye units. For the ground vibrational state the microwave data lead to the following bond distances: C–H, 1.056±0.005Å; C≡C, 1.201±0.002A. The C–C and C–F distances were calculated from the measured moments of inertia for several assumed values of the FCF angle. Electron diffraction experiments were also made, and the intensity curves calculated for the assumed microwave models were compared with the observed visual curve. From the combination of microwave and electron diffraction results the best agreement was obtained with the following set of parameters: ∠FCF, 107.5°±1°; C–C, 1.464±0.02A; C–F, 1.335±0.01A.

Additional Information

© 1951 American Institute of Physics. Received 16 July 1951. The authors wish to express their gratitude to Professor Albert L. Henne of Ohio State University for generously supplying the sample of trifluoromethyl acetylene. Thanks are also due to Professors W. H. Pickering and H. V. Neher and Mr. Bart Locanthi for valuable counsel concerning electronic problems, and to Dr. Kenneth W. Hedberg for his help with the interpretation of the electron diffraction photographs. This work was supported in part by a grant from the Research Corporation, for which we are very grateful.

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