Microwave spectroscopy of the vinylperoxy radical, CH₂CHOO

Vinylperoxy radicals were produced in a pulsed supersonic jet by discharging a gas mixture of vinyl bromide and molecular oxygen largely diluted in the Ar or Ne buffer gas. Two conformers of the radical, s-<i>trans</i> and s-<i>cis</i>, were detected through their pure rotational transitions <i>via</i> Fourier-transform microwave spectroscopy. Fine and hyperfine components in the observed spectra were fully assigned and analyzed to determine precise molecular constants for each conformer. The Fermi coupling constants determined for the -CH₂ protons indicate that non-negligible unpaired spin density is located on the terminal carbon atom, although the radical is generally considered as the oxygen-centered radical. The intensities of the observed spectra are much weaker than expected, probably because most of nascent vinylperoxy radicals formed by the association of the vinyl radical and O₂ promptly dissociate either to the vinoxy radical and atomic oxygen, or to formaldehyde and the formyl radical, even under jet-cooled conditions.