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P. Thaddeus (Harvard-Smithsonian CfA)
Linear carbon chain molecules are the dominant fraction of the 125 molecules which have now been identified in interstellar clouds or circumstellar shells, and the only molecules which have been conclusively identified as carriers of optical diffuse interstellar bands are carbon chains (as discussed by Maier at this meeting). In our laboratory over the past two years we have succeeded in detecting 46 carbon chains by applying Fourier transform microwave spectroscopy to supersonic molecular beams of reactive species produced in a gas discharge. The radio spectrum of all - including hyperfine structure when present - has been measured to the point that the laboratory astrophysics is complete: very precise rest frequencies are in hand for astronomical searches, and six of the chains have in fact already been detected with large radio telescopes. Because the longer chains tend to have their strongest lines at low frequencies, the resurfaced Arecibo telescope and the Green Bank Telescope under construction promise to be especially effective search instruments. Carbon chains are by far the best candidates for the several hundred diffuse bands which have been identified since 1922, and since the chain densities achieved in the laboratory are fairly high by the standards of laser spectroscopy, the classical problem of the diffuse bands may be on the point of general solution.
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