Microwave spectra, hyperfine splittings and average structures of 3,3,3-trifluoropropyne, CF3CCH and trifluoroacetonitrile, CF3CN

Abstract

The J= 1 â†� 0 and J= 2 â†� 1 microwave transitions of eight isotopomers of CF₃CCH and six isotopomers of CF₃CN have been investigated under high resolution using a pulsed-nozzle Fourier-transform spectrometer. High-precision isotopic measurements including the previously unobserved species ¹³CF₃CCH have enabled a complete calculation of the zero-point average structure of CF₃CCH: r(CC)= 1.201 (1)Å; r(C—C)= 1.474 (5)Å; r(C—H)= 1.051 (2)Å; ∠ FCF = 108.3 (2)°; r(C—F)= 1.337 (2)Å. For CF₃CCD deuterium quadrupole hyperfine structure was resolved and measured at the J= 1 â†� 0 transition, giving eQq(D)= 201.9 (5.2) kHz.

The zero-point average structure of CF₃CN has also been calculated from the high-resolution isotopic data after the necessary vibrational corrections: r(CN)= 1.154 (1)Å; r(C—C)= 1.492 (5)Å; ∠FCF = 109.2 (2)°; r(C—F)= 1.328 (2)Å. Measurements at the J= 1 â†� 0 transition give an improved value for the nitrogen quadrupole coupling constant, eQq(¹⁴N)=–4.666 (4) MHz, in CF₃CN.