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 transform microwave spectrometer. Twelve rotational transitions in the frequency range 6–12 GHz, all split by lambda-type doubling and with resolved hyperfine structure in the lowest transitions, were assigned to C11H in its 2Π electronic ground state. Detection of this highly unsaturated reactive carbon chain establishes that linear radicals containing up to 11 carbon atoms are stable isomers. The density of C11H in our molecular jet is probably sufficiently high for detection of the electronic transitions of this radical by standard laser spectroscopic techniques.