THE MICROWAVE-SPECTRUM, DIPOLE-MOMENT, MOLECULAR-STRUCTURE, AND HARMONIC FORCE-FIELD OF SELENONYL FLUORIDE, SEO2F2

The pure rotational spectrum of the reactive molecule selenonyl fluori de, SeO2F2, has been observed for the first time. We have measured R-b ranch transitions for five isotopic species of SeO2F2 in the 16-80 GHz frequency range. Analyses of these data yielded values for the rotati onal constants and quartic centrifugal distortion constants for all fi ve species. Each species is an oblate symmetric rotor whose dipole mom ent is directed along the a-inertial axis. From an analysis of the Sta rk shift data the molecular dipole moment has been evaluated as 0.593( 9) D. Values obtained for the quartic distortion constants have been c ombined with existing vibrational data to determine partially the harm onic force field of the SeO2F2 molecule. The ground state effective an d ground state average molecular geometries have been calculated, as h as the substitution coordinate of the selenium atom and an approximate equilibrium structure. Our microwave results demonstrate clearly that the molecule has C-2 upsilon symmetry. The ground state average struc tural parameters of SeO2F2 are: r(z)(SeO) = 1.5748(9) Angstrom, r(z)(S eF) = 1.6904(9) Angstrom, angle(OSeO) = 126.47(10)degrees, and angle(F SeF) = 93.72(4)degrees. (C) 1995 Academic Press, Inc.