Pure rotational spectra of the CCCF radical

Pure rotational transitions of a new carbon-chain radical CCCF in a supersonic jet have been observed for the first time using a Fourier-transform microwave spectrometer with a pulsed-discharge nozzle. The radical was produced by a pulsed electric discharge in a C(2)H(2) and CF(4) mixture diluted to 0.1% and 0.1% with Ne, respectively. Rotational transitions with spin and hyperfine splittings have been observed in the region from 9.1 GHz for N(K(a)K(c)) = 1(01)-0(00) to 27.3 GHz for N(K(a)K(c)) = 3(03)-2(02). The rotational constant, the spin-rotation interaction constant, and the hyperfine coupling constants due to the F nucleus have been precisely determined from the least-squares analysis, yielding B = 4555.8043(44), gamma(eff) = -7.105(16), b(F,eff) = 368(19), and c(eff) = -284.832(61) MHz. The determined molecular constants were compared with those obtained from high-level ab initio calculations and concluded that the CCCF radical has a bent ground state X(2)A(').