Rotational Spectrum of the Phenoxy Radical

We
report the hyperfine-resolved rotational spectrum of the gas-phase
phenoxy radical in the 8–25 GHz frequency range using
cavity Fourier transform microwave spectroscopy. A complete assignment
of its complex but well-resolved fine and hyperfine splittings yielded
a precisely determined set of rotational constants, spin-rotation
parameters, and nuclear hyperfine coupling constants. These results
are interpreted with support from high-level quantum chemical calculations
to gain detailed insight into the distribution of the unpaired π
electron in this prototypical resonance-stabilized radical. The accurate
laboratory rest frequencies enable studies of the chemistry of phenoxy
in both the laboratory and space. The prospects of extending the present
experimental and theoretical techniques to investigate the rotational
spectra of isotopic variants and structural isomers of phenoxy and
other important gas-phase radical intermediates that are yet undetected
at radio wavelengths are discussed.