DOI: 10.1002/mrc.2304

Resolving an apparent discrepancy between theory and experiment: spin-spin coupling constants for FCCF

Ab initio equation of motion coupled cluster singles and doubles (EOM–CCSD) and second-order polarization propagator approximation (SOPPA) calculations have been performed to evaluate spin–spin coupling constants for FCCF (difluoroethyne). The computed EOM-CCSD value of ³J(FF) obtained at the experimental geometry of this molecule supports the previously reported experimental value of 2.1 Hz, thereby resolving an apparent discrepancy between theory and experiment. This coupling constant exhibits a strong dependence on the CC and CF distances, and its small positive value results from a sensitive balance of paramagnetic spin-orbit (PSO) and spin-dipole (SD) terms. The three other unique FCCF coupling constants ¹J(CC), ¹J(CF), and ²J(CF) have also been reported and compared with experimental data. While ¹J(CF) is in agreement with experiment, the computed value of ²J(CF) is larger than our estimate of the experimental coupling constant.