Rotational spectra of gauche perfluoro-n-butane, C4F10; perfluoro-iso-butane, (CF3)3CF; and tris(trifluoromethyl)methane, (CF3)3CH

The microwave spectra of the gauche conformer of perfluoro-n-butane, n-C4F10, of perfluoro-iso-butane, (CF3)3CF, and of tris(trifluoromethyl)methane, (CF3)3CH, have been observed and assigned. The rotational and centrifugal distortion constants for gauche n-C4F10 are: A = 1058.11750(7) MHz, B = 617.6832(1) MHz, C = 552.18794(1) MHz, ΔJ = 0.0257(5) kHz, δJ = 0.0052(3) kHz. A C-C-C-C dihedral angle, ω, of ∼55° has been determined. These values agree well with those obtained from a coupled cluster (CCSD/cc-PVTZ) calculation. The rotational and centrifugal distortion constants for iso-C4F10 and iso-C4HF9 are: Bo = 816.4519(4) MHz, DJ = 0.023(2) kHz, and Bo = 903.6985(25) MHz, DJ = 0.043(4) kHz, respectively. The dipole moment of iso-C4F10 and iso-C4HF9 have been measured and found to be 0.0338(8) and 1.69(9) D, respectively.