Phenyl Radicals Over the Radio

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Science  27 Jun 2003:
Vol. 300, Issue 5628, pp. 2007
DOI: 10.1126/science.300.5628.2007c

The polyaromatic hydrocarbons (PAHs) found in space are thought to form through reaction pathways that include the phenyl radical C6H5. This radical has been well characterized by a variety of optical and infrared spectroscopic techniques, but unfortunately not in the frequency range needed for radio astronomy, which probes signatures of molecular rotation. One difficulty is the preparation of this unstable radical species for spectral analysis. McMahon et al. have now detected phenyl radical in a benzene glow discharge using Fourier-transform microwave spectroscopy and millimeter-wave absorption spectroscopy. By optimizing the discharge conditions, they minimized the formation of other species, such as o-benzyne, and obtained rotational constants for the phenyl radical, in part by identifying more than 50 rotational transitions between 150 and 330 Ghz. Encouragingly, some of these lines are sufficiently intense to be observable in millimeter-wave spectroscopy.—PDS

Astrophys. J. 590, L61 (2003).

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