The Microwave Spectrum, Dipole Moment, Molecular Structure, and Harmonic Force Field of Selenonyl Fluoride, SeO 2F 2

The pure rotational spectrum of the reactive molecule selenonyl fluoride, SeO₂F₂, has been observed for the first time. We have measuredR-branch transitions for five isotopic species of SeO₂F₂in the 16-80 GHz frequency range. Analyses of these data yielded values for the rotational constants and quartic centrifugal distortion constants for all five species. Each species is an oblate symmetric rotor whose dipole moment is directed along thea-inertial axis. From an analysis of the Stark shift data the molecular dipole moment has been evaluated as 0.593(9) D. Values obtained for the quartic distortion constants have been combined with existing vibrational data to determine partially the harmonic force field of the SeO₂F₂molecule. The ground state effective and ground state average molecular geometries have been calculated, as has the substitution coordinate of the selenium atom and an approximate equilibrium structure. Our microwave results demonstrate clearly that the molecule hasC_2vsymmetry. The ground state average structural parameters of SeO₂F₂are:r_z(SeO) = 1.5748(9) Å,r_z(SeF) = 1.6904(9) Å,[formula](OSeO) = 126.47(10)°, and[formula](FSeF) = 93.72(4)°.