15min:

FILIPPO TAMASSIA, JOHN M. BROWN, The Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ UK; KENNETH M. EVENSON, NIST, 325 Broadway, Boulder, CO 80303, USA.

The fine-structure transition ²_1/2<-~²_3/2 of the free radical FO has been detected by far-infrared Laser Magnetic Resonance. The spectrum is entirely magnetic dipole and several pure rotational transitions ranging between J=\frac12 and J=20~\frac12 have been recorded in both perpendicular and parallel polarization. These data form the most accurate spectroscopic information available for FO. A set of 272 transitions have been analyzed using a linear least-sqares fit. The Hamiltonian, which contains rotational, centrifugal distortion, spin-orbit, \Lambda-doubling, magnetic hyperfine and Zeeman terms, was set up in a decoupled basis set. The spin-orbit coupling constant A₀, the magnetic hyperfine parameters a, b_F, c, d and a number of g -factors have been derived experimentally for the first time. The value of A₀ obtained from the fit is: \begincenter A₀=-196.108690(50) cm^-1. \endcenter