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 2Π 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 2Π3/2 for C10H, C12H, and C14H, and 2Π1/2 for C13H. Only three spectroscopic constants in the standard Hamiltonian for a molecule in a 2Π state were required to reproduce the spectra to a few parts in 107: 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 ⩾5×109 per gas pulse, which suggests that optical transitions of all four may be detecta...