ESR Spectrum and Structure of O2F

The electron spin resonance (ESR) spectrum of the dioxygen monofluoride radical (O2F) has been observed in an argon matrix at 4.2°K. The radical was produced by the reaction of O2 with fluorine atoms obtained from the photolytic decomposition of F2. Computer analysis of the spectrum gave the following values for the components of the g factor and fluorine hyperfine-splitting tensors: g1=2.0080, g2=2.0008, and g3=2.0022; A1/h=±288.4, A2/h=∓141.1, and A3/h=∓39.2 Mc/sec. Theoretical considerations suggest that A1 is negative, and that Axis 1 lies along the O–F bond, Axis 2 is perpendicular to the molecular plane, and Axis 3 lies along the O–O bond. The ESR spectrum of O2F was found to contain normally ``forbidden'' lines in which the electron spin transition is accompanied by a nuclear spin flip. These lines may be responsible for some of the complicated changes in the appearance of this spectrum which accompany changes in temperature and matrix. By using the experimental value of g3 to evaluate a critical parameter in a semiempirical molecular-orbital treatment of O2F, values were obtained for the charge distribution and bond order in this radical. The results agree with conclusions drawn from infrared spectroscopy, and suggest that this radical is stabilized by resonance which permits the fluorine to form a weak O–F bond without any loss of the O–O bond strength.