Rotational spectra of the carbon chain free radicals C10H, C12H, C13H, and C14H

The four carbon chain radicals C10H, C12H, C13H, and C14H have been observed in a pulsed supersonic molecular beam with a Fourier transform microwave spectrometer. The radicals were produced in a discharge through a dilute diacetylene/neon mixture in the throat of a supersonic nozzle. All are linear with (2)Pi electronic ground states, and all except C14H have resolved lambda-type doubling. For each species at least ten rotational transitions, between 6 and 16 GHz, were measured in the lowest spin component, which is (2)Pi(3/2) for C10H, C12H, and C14H, and (2)Pi(1/2) for C13H Only three spectroscopic constants in the standard Hamiltonian for a molecule in a (2)Pi state were required to reproduce the spectra to a few parts in 10(7): an effective rotational constant, a centrifugal distortion constant, and a lambda-type doubling constant. All of the chains here have abundances in the most intense part of the supersonic molecular beam of greater than or equal to 5 x 10(9) per gas pulse, which suggests that optical transitions of all four may be detectable with present laser techniques. For the carbon chain radicals with an even number of carbon atoms, there is very little change in relative abundance from C6H to C14H. (C) 1998 American Institute of Physics. [S0021-9606(98)00230-X].