MICROWAVE SPECTROSCOPY OF THE CARBON-CHAIN RADICAL C11H

The pure rotational spectrum of the carbon chain radical C11H has been observed in a pulsed supersonic molecular beam with a Fourier transfo rm microwave spectrometer. Twelve rotational transitions in the freque ncy range 6-12 GHz, all split by lambda-type doubling and with resolve d hyperfine structure in the lowest transitions, were assigned to C11H in its (II)-I-2 electronic ground state. Detection of this highly uns aturated reactive carbon chain establishes that linear radicals contai ning up to 11 carbon atoms are stable isomers. The density of C11H in our molecular jet is probably sufficiently high for detection of the e lectronic transitions of this radical by standard laser spectroscopic techniques.