Rotation-vibration spectra and rotational, Coriolis coupling and potential constants of ethane, ethane-d6 and ethane-1, 1, 1-d3

The infrared spectra of CH 3 CH 3 , CD 3 CD 3 and CH 3 CD 3 have been measured under medium resolution (∼0.4 cm −1 ). The rotation-vibration bands have been analysed, and the rotational constants B ″ have been obtained from the parallel bands. By using the A ″ values determined by Welsh et al. , the Coriolis constants for the degenerate vibrations have been determined from the analysis of a successive series of Q branches for the perpendicular bands. A normal coordinate analysis has been made and the potential constants on the basis of the local symmetry force field (LSFF) have been obtained from the fundamental frequencies and the Coriolis constants of CH 3 CH 3 and CD 3 CD 3 . These potential constants have been checked by the comparison of the calculated values of CH 3 CD 3 with the observed. The potential constants and the Coriolis constants have been discussed in connection with some related molecules such as CH 3 X and CH 3 CN.