Analysis of the rotational structure in the high-resolution infrared spectra of cis,cis- and trans,trans-1,4-difluorobutadiene-1-d1 and trans,trans-1,4-difluorobutadiene-1,4-d2

Samples of cis , cis - and trans , trans -1,4-difluorobutadiene-1- d 1 and of trans , trans -1,4-difluorobutadiene-1,4- d 2 have been synthesized, and high-resolution (⩽0.0018 cm −1 ) infrared spectra of these substances have been recorded in the gas phase. Analysis of the rotational structure, mostly in C-type bands, has yielded ground state rotational constants. For the two 1-d 1 species more than one band has been analyzed. For the 1,4-d 2 species only one band was available for analysis. However, good agreement between the experimental centrifugal distortion constants and those predicted with a B3LYP/cc-pVTZ model give strong support to the analysis of the very dense spectrum. The ground state rotational constants are a contribution to finding semiexperimental equilibrium structures of the two nonpolar isomers of 1,4-difluorobutadiene.