Hyperfine-Resolved Rotational Spectroscopy of Phenyl Radical.

We present an analysis of the hyperfine-resolved rotational spectrum of gas-phase phenyl radical, c -C 6 H 5 , between 9 and 35 GHz. The isotropic and anisotropic hyperfine parameters of all five protons and the electronic spin-rotation fine structure parameters are accurately determined from this study, which allow detailed insight into the distribution and interactions of the unpaired electron in this prototypical σ-radical. The implications for laboratory and astronomical investigations of phenyl that are reliant on a precise centimeter-wave catalog are discussed, as are the prospects for detecting and assigning the hyperfine-resolved rotational spectra of other large, weakly polar hydrocarbon chain and ring radicals.