Complete structure of anti-1,1,2,2-tetrafluoroethane by high-resolution infrared spectroscopy

High-resolution (0.0018 cm(-1)) infrared spectra have been recorded in the CF stretching region for 1,1,2,2-tetrafluoroethane and its d(2) and C-13(2) isotopomers. These bands are sufficiently intense to give useful gasphase spectra at -100 degreesC in a 3 m cell. For each spectrum the rotational st ructure of the A/C-type and B-type bands due to the anti rotamer, which is a highly asymmetric rotor with kappa = -0.295, have been analyzed. Rotation al constants for a Watson-type Hamiltonian have been fitted for the common ground state of each isotopomer and the separate upper states. A complete s tructure for the nonpolar anti rotamer has been derived and compared with t he structure of the polar gauche rotamer obtained from microwave spectrosco py, The geometric parameters for the anti rotamer are r(CH) 1.087(5) Angstr om, r(CC) = 1.511(4) Angstrom, r(CF) = 1.359(7) Angstrom, alpha (CCH) = 112 .9(3)degrees, alpha (CCF) = 108.5(6)degrees, alpha (FCF) = 107.4(6)degrees, and tau (CCF) = 63.6(12)degrees. The structural parameters for the two iso mers of 1,1,2,2-tetrafluoroethane are compared with recent calculations, an d trends in these parameters and those of the rotamers of 1,2-difluoroethan e are discussed.