Fine and hyperfine coupling constants of the cis -β-cyanovinyl radical, HCCHCN.

A Fourier-transform microwave spectrum of the cis -β-cyanovinyl radical is re-measured for the K a = 0 ladder of the a-type transitions up to 30 GHz and the 2 12 -1 11 transition at 19.85 GHz. Four b-type transitions are also observed using a MW-MW double-resonance technique. Fine and hyperfine components observed for each rotational transition are fully assigned in the present study, and the precise molecular constants are determined for the radical. From the comparisons of the hyperfine coupling constants with those of the vinyl radicals, it is concluded that the substitution of one of the β-hydrogens by the cyano group has little effect on the electronic structure of the vinyl radical.