Rotational analysis of bands in the high-resolution infrared spectra of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d1

Abstract

Pure samples of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d1 have been synthesized, and high-resolution (0.0015cm−1) infrared spectra have been recorded for these nonpolar molecules in the gas phase. For the cis,cis isomer, the rotational structure in two C-type bands at 775 and 666cm−1 and one A-type band at 866cm−1 has been analyzed to yield a combined set of 2020 ground state combination differences (GSCDs). Ground state rotational constants fit to these GSCDs are A0=0.4195790(4), B0=0.0536508(8), and C0=0.0475802(9)cm−1. For the trans,trans isomer, three C-type bands at 856, 839, and 709cm−1 have been investigated to give a combined set of 1624 GSCDs. Resulting ground state rotational constants for this isomer are A0=0.9390117(8), B0=0.0389225(4), and C0=0.0373778(3)cm−1. Small inertial defects confirm the planarity of both isomers in the ground state. Upper state rotational constants have been determined for most of the transitions. The ground state rotational constants for the two isotopologues will contribute to the data set needed for determining semiexperimental equilibrium structures for the nonpolar isomers of 1,4-difluorobutadiene.